GLP-1 Studies Explained: The Complete Evidence Guide (2026 Edition)
Semaglutide, tirzepatide, oral GLP-1 medicines, retatrutide and the next generation of metabolic therapies have changed the obesity and cardiometabolic treatment landscape. But the phrase “GLP-1 drug” can hide major differences in mechanism, indication, dose, study population and clinical evidence.
This master guide organizes the most important clinical trials into an ebook-style reference—from the landmark STEP and SURMOUNT obesity trials to SELECT, FLOW, SUMMIT, ESSENCE, OASIS 4, ATTAIN-1, TRIUMPH, SURPASS and the emerging CagriSema program.
Last reviewed: September 23, 2026. Regulatory status is jurisdiction-specific and can change.
Chapter 1 — What “GLP-1” Actually Means
Chapter 2 — How to Read the GLP-1 Evidence
Chapter 3 — The Landmark Weight-Loss Trials
Chapter 4 — Why Weight Maintenance Matters
Chapter 5 — Cardiovascular Outcomes
Chapter 6 — Kidney Outcomes
Chapter 7 — Heart Failure, Sleep Apnea and Functional Outcomes
Chapter 8 — Metabolic Liver Disease
Chapter 9 — Tirzepatide and Type 2 Diabetes
Chapter 10 — The Oral GLP-1 Era
Chapter 11— Higher-Dose Semaglutide
Chapter 12 — Retatrutide: The Triple-Agonist Frontier
Chapter 13 — CagriSema and Amylin-Based Next-Generation Therapies
Chapter 14 — Safety: What the Trials and FDA Updates Actually Show
Chapter 15 — Muscle, Nutrition and Treatment Quality
Chapter 16 — Cancer and Brain Research
Chapter 17 — The Master GLP-1 Evidence Map
Chapter 18 — What We Know, What We Don't Know and What Comes Next
Chapter 19 — Frequently Asked Questions
Key Studies and Primary Sources
Chapter 1 What “GLP-1” Actually Means
GLP-1 stands for glucagon-like peptide-1, an incretin hormone involved in glucose regulation, appetite and gastrointestinal function. GLP-1 receptor agonists mimic important actions of this pathway, including increasing glucose-dependent insulin secretion, reducing glucagon secretion, slowing gastric emptying to varying degrees and influencing appetite-regulating circuits.
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The modern obesity-drug landscape, however, is broader than classic GLP-1 receptor agonists. Semaglutide is a GLP-1 receptor agonist; tirzepatide activates both GIP and GLP-1 receptors; retatrutide targets GIP, GLP-1 and glucagon receptors; and CagriSema combines semaglutide with the amylin analogue cagrilintide.
| Therapy | Mechanism | Route | 2026 U.S. status | Main evidence focus |
|---|---|---|---|---|
| Semaglutide | GLP-1 receptor agonist | Injection / tablet | Approved | Obesity, type 2 diabetes, cardiovascular risk reduction, kidney outcomes, MASH |
| Tirzepatide | GIP + GLP-1 receptor agonist | Injection | Approved | Obesity, type 2 diabetes, obstructive sleep apnea and expanding cardiometabolic evidence |
| Liraglutide | GLP-1 receptor agonist | Injection | Approved | Diabetes, obesity and cardiovascular outcomes |
| Orforglipron / Foundayo | Oral small-molecule GLP-1 receptor agonist | Tablet | Approved | Oral obesity treatment |
| Retatrutide | GIP + GLP-1 + glucagon receptor agonist | Injection | Investigational | Next-generation obesity and metabolic disease research |
| CagriSema | Semaglutide + cagrilintide | Injection | Investigational | Weight management and type 2 diabetes |
FDA approval status should never be inferred simply from a strong trial result. A Phase 3 trial can demonstrate efficacy and safety within a study population without automatically making a medicine approved or commercially available.
FDA: 2026 novel drug approvals
Chapter 2 How to Read the GLP-1 Evidence
One of the biggest problems in GLP-1 coverage is that completely different types of evidence are often mixed together. A dramatic laboratory mechanism, a social-media testimonial, a small observational study and a large randomized trial do not carry the same evidentiary weight.
What matters most in a clinical trial?
Start with five questions:
- Who was studied?
- Which molecule and dose were used?
- What was the comparator?
- What outcome was measured?
- How long were participants followed?
A change in weight, blood pressure or HbA1c may be clinically useful, but these surrogate or intermediate outcomes are not equivalent to demonstrating fewer heart attacks, kidney failures, hospitalizations or deaths.
OneDayMD E0–E5 evidence framework
| Grade | Evidence type | How to interpret it |
|---|---|---|
| E5 | Large randomized controlled trial with clinically meaningful outcomes | High-confidence evidence for the studied population and endpoint |
| E4 | Strong prospective or randomized evidence with important limitations | Strong evidence, but interpretation requires context |
| E3 | Observational studies, secondary analyses or heterogeneous meta-analyses | Useful evidence, but vulnerable to confounding and indirectness |
| E2 | Small trials, exploratory analyses or uncontrolled cohorts | Hypothesis-generating |
| E1 | Animal, laboratory or mechanistic research | Biological evidence, not proof of human clinical benefit |
| E0 | Testimonials, anecdotes, influencer claims or unsupported marketing | Not sufficient to establish efficacy |
This framework is especially useful when reading headlines about next-generation molecules such as retatrutide. A company-reported topline Phase 3 result may be highly interesting while still having less independent detail than a fully published peer-reviewed trial.
Chapter 3 The Landmark Weight-Loss Trials
The STEP and SURMOUNT programs established the modern benchmark for pharmacologic weight management. They also demonstrated why obesity treatment should be understood as chronic disease management rather than a short cosmetic intervention.
STEP-1 — Semaglutide and obesity
STEP-1 randomized 1,961 adults with overweight or obesity without diabetes to weekly semaglutide 2.4 mg or placebo, alongside lifestyle intervention, for 68 weeks. Mean weight change was approximately −14.9% with semaglutide versus −2.4% with placebo.
The trial was a turning point because it showed that pharmacologic treatment could generate weight losses much greater than those typically seen with older anti-obesity medications.
SURMOUNT-1 — Tirzepatide and obesity
SURMOUNT-1 evaluated tirzepatide in 2,539 adults with obesity or overweight plus a weight-related complication who did not have type 2 diabetes. Participants received 5 mg, 10 mg, 15 mg or placebo for 72 weeks.
Weight loss increased with dose, with the greatest average reduction at the highest studied dose. Gastrointestinal adverse events were among the most common side effects.
SURMOUNT-5 — Tirzepatide versus semaglutide
Direct head-to-head trials are particularly valuable because they reduce one major problem with cross-trial comparisons. SURMOUNT-5 randomized adults with obesity without type 2 diabetes to maximum tolerated doses of tirzepatide or semaglutide for 72 weeks.
Mean weight change at 72 weeks.
Mean weight change at 72 weeks.
Randomized comparison in adults with obesity without diabetes.
Tirzepatide produced greater average weight reduction in this trial. The correct interpretation, however, is not that one medicine is automatically preferable for every individual. The result applies to the population, doses and conditions studied.
PubMed: SURMOUNT-5 · NEJM: SURMOUNT-5
Chapter 4 Why Weight Maintenance Matters
One of the most important lessons from the GLP-1 literature is easy to miss: weight loss during treatment and weight maintenance after treatment are different questions.
Semaglutide withdrawal
In the STEP-1 extension, a representative subset of participants was followed for another year after treatment stopped. Participants who had received semaglutide regained a substantial portion of the weight they had lost. At week 120, they had regained approximately two-thirds of the previous weight reduction.
The cardiometabolic improvements observed during treatment also moved back toward baseline for many variables after withdrawal.
PubMed: STEP-1 withdrawal extension
SURMOUNT-4 — Tirzepatide withdrawal
SURMOUNT-4 used a randomized withdrawal design. After an initial 36-week tirzepatide lead-in period, participants who stopped active treatment and switched to placebo regained substantial weight, while participants who continued tirzepatide maintained and extended their weight reduction.
Among those randomized at week 36, mean weight change from week 36 to week 88 was approximately −5.5% with continued tirzepatide versus +14.0% after switching to placebo.
Chapter 5 Cardiovascular Outcomes
The GLP-1 field changed again when researchers began asking not simply whether patients lost weight, but whether treatment reduced major cardiovascular events.
SELECT — Semaglutide and cardiovascular disease
SELECT enrolled 17,604 adults with overweight or obesity and established cardiovascular disease who did not have diabetes. Participants received weekly semaglutide 2.4 mg or placebo.
The primary cardiovascular endpoint—cardiovascular death, nonfatal myocardial infarction or nonfatal stroke—occurred in 6.5% of the semaglutide group and 8.0% of the placebo group, corresponding to a hazard ratio of 0.80.
This is an important distinction: SELECT demonstrated a difference in clinical cardiovascular events, not merely improved cholesterol, blood pressure or body weight.
NEJM: SELECT (2023) · FDA: Wegovy cardiovascular indication
The broader GLP-1 cardiovascular evidence base
Earlier cardiovascular outcome programs also established clinically important effects for some GLP-1 receptor agonists in high-risk people with type 2 diabetes. Examples include LEADER with liraglutide, SUSTAIN-6 with semaglutide and REWIND with dulaglutide.
These studies should not be treated as interchangeable. Different drugs, populations, background therapies and baseline cardiovascular risk produce different clinical contexts.
NEJM: LEADER (2016)
Anti-inflammatory effects of tirzepatide: a systematic review and meta-analysis
Chapter 6 Kidney Outcomes
FLOW — Semaglutide and chronic kidney disease
FLOW studied people with type 2 diabetes and chronic kidney disease. The trial evaluated whether semaglutide could reduce important kidney and cardiovascular outcomes rather than simply changing laboratory markers.
The results expanded the role of semaglutide into kidney-risk management for a specific high-risk population. They should not automatically be extrapolated to every person taking a GLP-1 medicine.
Chapter 7 Heart Failure, Sleep Apnea and Functional Outcomes
STEP-HFpEF — Semaglutide and obesity-related HFpEF
STEP-HFpEF randomized 529 patients with obesity and heart failure with preserved ejection fraction to semaglutide 2.4 mg or placebo for 52 weeks.
Semaglutide improved heart-failure symptoms and physical limitations, increased exercise capacity and produced substantially more weight loss than placebo.
STEP-HFpEF DM
A related trial studied people with obesity-related HFpEF and type 2 diabetes. Semaglutide again improved heart-failure symptoms and physical limitations while producing greater weight loss than placebo.
SUMMIT — Tirzepatide and HFpEF
SUMMIT evaluated tirzepatide in adults with obesity and HFpEF. The trial found a lower risk of the composite of cardiovascular death or worsening heart-failure events, with the difference driven mainly by fewer worsening heart-failure events. Tirzepatide also improved symptoms, physical limitations and body weight.
SURMOUNT-OSA — Obstructive sleep apnea
Obesity is closely linked to obstructive sleep apnea. In the SURMOUNT-OSA program, tirzepatide reduced the apnea-hypopnea index, body weight and other disease-related measures in adults with obesity and moderate-to-severe sleep apnea.
The FDA subsequently approved Zepbound for moderate-to-severe obstructive sleep apnea in adults with obesity.
NEJM: SURMOUNT-OSA · FDA: Zepbound and OSA
Chapter 8 GLP-1 Drugs and Metabolic Liver Disease
ESSENCE — Semaglutide and MASH
Metabolic dysfunction-associated steatohepatitis, or MASH, has become one of the most important new frontiers for incretin-based treatment.
In the Phase 3 ESSENCE trial, semaglutide 2.4 mg was studied in adults with biopsy-defined MASH and stage 2 or 3 liver fibrosis. The study found meaningful histologic improvement in MASH-related endpoints.
The FDA subsequently approved Wegovy injection for adults with non-cirrhotic MASH and moderate-to-advanced fibrosis under the accelerated approval pathway.
The distinction matters because histologic improvement is not the same as proving reductions in cirrhosis, liver transplantation or mortality. The confirmatory outcomes work therefore remains important.
NEJM: ESSENCE · FDA: Wegovy and MASH
Chapter 9 The SURPASS Trials: Tirzepatide and Type 2 Diabetes
The SURPASS program is tirzepatide's phase 3 registration package for type 2 diabetes, encompassing five global trials (SURPASS-1 through -5, over 6,200 participants combined) plus the newer, dedicated cardiovascular outcomes trial, SURPASS-CVOT. Because tirzepatide activates both the GIP and GLP-1 receptors, the SURPASS program consistently shows larger HbA1c and weight reductions than semaglutide's SUSTAIN/STEP data — a pattern confirmed directly in SURPASS-2's head-to-head design.
SURPASS-1 through -5: the glycemic and weight evidence
- SURPASS-1 (478 participants, monotherapy vs. placebo): HbA1c fell by 1.87%, 1.89%, and 2.07% at the 5 mg, 10 mg, and 15 mg doses respectively, versus a 0.04% increase with placebo. Weight fell 7–9.5 kg, and 81–86% of tirzepatide-treated participants reached an HbA1c of 6.5% or below.
- SURPASS-2 (1,879 participants, head-to-head vs. semaglutide 1 mg over 40 weeks): all three tirzepatide doses produced statistically superior HbA1c and weight reductions compared with semaglutide 1 mg — the first phase 3 evidence that a GIP/GLP-1 dual agonist could outperform a best-in-class GLP-1-only drug.
- SURPASS-3 (1,444 participants, vs. titrated insulin degludec over 52 weeks): the 15 mg dose reduced HbA1c by 2.37% and body weight by 12.9 kg (13.9%) — a notable result because insulin typically causes weight gain, not loss.
- SURPASS-4 (2,002 participants, vs. titrated insulin glargine, high cardiovascular-risk population): tirzepatide again produced superior glycemic and weight outcomes versus glargine. The trial wasn't statistically powered for cardiovascular superiority, but exploratory analyses showed a favorable trend toward fewer MACE events with tirzepatide versus glargine — a signal that helped justify running the dedicated SURPASS-CVOT trial described below.
- SURPASS-5 (tirzepatide added to titrated insulin glargine, 40 weeks): the 15 mg dose reduced HbA1c by 2.59% and body weight by 10.9 kg (11.6%), with more than 85% of participants across all three tirzepatide doses reaching an HbA1c below 7%.
Pooled across SURPASS-1 to -5, the proportion of participants who reached an HbA1c under 7% with at least 5% weight loss and without hypoglycemia — a demanding composite endpoint — ranged from 43% to 82% with tirzepatide, versus just 4–5% with placebo.
SURPASS-CVOT: tirzepatide's cardiovascular outcomes trial (new, December 2025)
For years, tirzepatide carried strong glycemic and weight data but lacked a dedicated cardiovascular outcomes trial — unlike semaglutide, which had SUSTAIN-6 and then SELECT. That gap closed with SURPASS-CVOT, published in the New England Journal of Medicine in December 2025 (Nicholls et al.). This was a head-to-head, active-comparator trial — not placebo-controlled — comparing tirzepatide (up to 15 mg) against dulaglutide 1.5 mg, a GLP-1 drug with its own established cardiovascular benefit (from the earlier REWIND trial), in 13,299 adults with type 2 diabetes and established atherosclerotic cardiovascular disease, followed for a median of about four years across 640 sites in 30 countries.
- Primary outcome (3-point MACE): occurred in 12.2% of the tirzepatide group versus 13.1% of the dulaglutide group — HR 0.92 (95.3% CI, 0.83–1.01). This met the trial's prespecified noninferiority threshold (P = 0.003) but did not reach statistical significance for superiority (P = 0.09) — an important nuance discussed further below.
- All-cause mortality: reduced by 16% with tirzepatide (HR 0.84, 95% CI 0.75–0.94, P = 0.002) — a prespecified secondary endpoint that did reach significance.
- Post hoc cardiorenal composite analysis: after a median treatment duration of about 47 months, this broader composite occurred in 23.7% of the tirzepatide group versus 27.4% of the dulaglutide group (HR 0.84, 95% CI 0.79–0.90).
- Tirzepatide also produced greater reductions in HbA1c, body weight, blood pressure, and lipids than dulaglutide, along with a favorable trend in eGFR slope — an early kidney-protection signal that mirrors what FLOW later confirmed for semaglutide.
Chapter 10 The Oral GLP-1 Era
One of the biggest changes in 2026 is that effective obesity treatment is no longer defined exclusively by weekly injections.
Wegovy tablets — oral semaglutide
Wegovy tablets contain semaglutide and were approved in the United States in late 2025, followed by broad U.S. availability beginning in January 2026. The 25 mg tablet was supported by the OASIS program and the broader semaglutide evidence base, including SELECT.
OASIS 4 studied daily oral semaglutide 25 mg in adults with overweight or obesity without diabetes. The trial demonstrated substantial weight loss, expanding the evidence base for oral semaglutide in obesity treatment.
FDA: Wegovy tablets approval letter · NEJM: OASIS 4
Foundayo — orforglipron
Orforglipron represents another oral strategy. It is a small-molecule, nonpeptide GLP-1 receptor agonist designed for once-daily oral dosing.
In ATTAIN-1, once-daily orforglipron produced significantly greater weight reduction than placebo at 72 weeks, with gastrointestinal effects among the most common adverse events.
The FDA approved Foundayo (orforglipron) on April 1, 2026 for reducing excess body weight and maintaining weight reduction long term in adults with obesity or adults with overweight and at least one weight-related comorbidity, in combination with reduced-calorie diet and increased physical activity.
NEJM: ATTAIN-1 · FDA: Foundayo approval
| Oral therapy | Mechanism | 2026 status | Key study | Important distinction |
|---|---|---|---|---|
| Wegovy tablets | Semaglutide / GLP-1 | FDA approved | OASIS 4 | Same semaglutide molecule used in the Wegovy family |
| Foundayo | Orforglipron / oral GLP-1 | FDA approved | ATTAIN-1 | Different small-molecule GLP-1 medicine |
Chapter 11 Retatrutide: The Triple-Agonist Frontier
Retatrutide is one of the most closely watched next-generation obesity medicines. It is a single molecule that activates GIP, GLP-1 and glucagon receptors.
The scientific rationale is that simultaneous action across several metabolic pathways may generate greater effects on body weight and metabolic disease than GLP-1-only treatment.
TRIUMPH-1
In the Phase 3 TRIUMPH-1 program, Lilly reported that participants receiving 12 mg retatrutide achieved approximately 28.3% average weight loss at 80 weeks. The result was company-reported topline data and should be distinguished from a fully published peer-reviewed trial report.
Lilly: TRIUMPH-1 results . NEJM: TRIUMPH-1 (September 2026)
TRIUMPH-2
In adults with obesity or overweight plus type 2 diabetes, Lilly reported average weight reductions of up to approximately 20.8% at 80 weeks with the highest studied dose.
TRIUMPH-3
In adults with severe obesity and established cardiovascular disease, with or without type 2 diabetes, Lilly reported average weight loss of up to approximately 22.6% at 80 weeks.
Lilly has said it plans to submit a Biologics License Application for retatrutide to the FDA in Q1 2027.
Lilly: TRIUMPH-2 and TRIUMPH-3
TRANSCEND-T2D-2
Eli Lilly and Company (NYSE: LLY), the maker of Mounjaro (tirzepatide) and Foundayo (orforglipron), announced positive topline results from TRANSCEND-T2D-2 in October 2026, a head-to-head Phase 3 trial comparing retatrutide with injectable Ozempic 2 mg in adults with type 2 diabetes. At 80 weeks, retatrutide met the primary and all key secondary endpoints, delivering greater A1C reduction and substantially more weight loss than Ozempic.TRANSCEND-T2D-1
TRANSCEND-T2D-1 was the first Phase 3 trial to test retatrutide specifically in adults with type 2 diabetes. On March 19, 2026, Eli Lilly announced that the trial met its primary endpoint and all key secondary endpoints. Retatrutide produced superior A1C reduction and weight loss compared to placebo across all doses tested. Full results were published in The Lancet on June 6, 2026.
TRIUMPH-4
In obesity with knee osteoarthritis (TRIUMPH-4, December 2025), participants taking retatrutide 12 mg lost an average of 28.7 percent of body weight at 68 weeks — about 71 pounds — with substantial reductions in pain and improvements in physical function.Retatrutide and Fatty Liver
In a Phase 2 substudy of fatty liver disease, an 86 percent reduction in liver fat. Ninety-three percent of treated patients normalized their livers. Seventy-two percent of prediabetics returned to normal blood sugar.
In June 2024, researchers led by Arun J. Sanyal published the results of a Phase 2a liver sub-study in Nature Medicine — and the data was extraordinary. The study enrolled 98 participants with obesity and elevated liver fat. They were randomly assigned to receive once-weekly subcutaneous injections of retatrutide (at doses of 1, 4, 8, or 12 mg) or placebo for 48 weeks. Liver fat was measured using MRI-proton density fat fraction (MRI-PDFF), which is the gold-standard imaging technique for quantifying hepatic steatosis.At the highest dose, retatrutide eliminated 86% of liver fat over 48 weeks — and 93% of participants achieved completely normal liver fat levels. Zero participants on placebo achieved normalisation.
Even at the lowest 1 mg dose, more than half of participants had normal liver fat by 48 weeks. And the data shows that most of the reduction happened in the first 24 weeks, with continued improvement to week 48 — suggesting that the liver responds rapidly to the drug's mechanisms.
FDA: Concerns with unapproved GLP-1 drugs · Lilly: What to know about retatrutide
Why retatrutide should be watched—but not confused with approved therapy
Retatrutide may eventually change expectations about how much weight pharmacotherapy can achieve. But efficacy estimates from investigational studies are not the same as an approval decision, long-term outcomes evidence, post-marketing safety data or real-world adherence.
The next important questions are therefore not only “How much weight can retatrutide reduce?” but also: How durable is the result? How does it compare directly with the best available therapies? What happens to lean mass? What are the long-term cardiovascular, renal and metabolic outcomes? And what is the full safety profile?
Chapter 12 Higher-Dose Semaglutide
Wegovy HD — semaglutide 7.2 mg
The GLP-1 innovation race is not only about inventing new molecules. Developers are also exploring whether higher doses can extend weight-loss efficacy.
In March 2026, the FDA approved Wegovy HD, a higher 7.2 mg dose of semaglutide injection, for weight loss and long-term maintenance of weight reduction in eligible adults with obesity or overweight plus a weight-related condition.
The FDA reported that the higher dose produced additional average weight reduction compared with previously approved doses, with a safety profile consistent with known semaglutide effects. Gastrointestinal adverse events remained important.
Chapter 13 CagriSema and Amylin-Based Next-Generation Therapies
Another major direction is combining GLP-1 biology with amylin pathway activation. CagriSema combines semaglutide with cagrilintide.
Why CagriSema matters
The strategy is different from simply increasing the semaglutide dose. Combining complementary hormonal pathways may influence appetite, satiety, food intake and body weight through partially distinct mechanisms.
September 2026 update
On September 21, 2026, Novo Nordisk reported topline Phase 3 data from REIMAGINE 5 and REDEFINE 9.
In REIMAGINE 5, among adults with type 2 diabetes, CagriSema 1.0 mg/1.0 mg produced an estimated average weight loss of 12.4% versus 9.1% with tirzepatide 5 mg at week 60.
In REDEFINE 9, CagriSema produced approximately 21% weight loss versus placebo at 68 weeks in adults with overweight or obesity.
Novo Nordisk: CagriSema REIMAGINE 5 and REDEFINE 9
As of this update, CagriSema remains investigational.
Chapter 14 Safety: What the Trials and FDA Updates Actually Show
GLP-1 medicines are not risk-free. But safety should be evaluated using clinical-trial data, prescribing information and regulator reviews rather than isolated anecdotes or sensational headlines.
Common adverse effects
| Issue | What is generally seen | Why it matters |
|---|---|---|
| Nausea | Common, particularly during dose escalation | Can affect adherence and food intake |
| Vomiting | Can occur, often during dose escalation | Persistent vomiting can contribute to dehydration and nutritional problems |
| Diarrhea | Common with several incretin therapies | May affect hydration and treatment tolerance |
| Constipation | Common in obesity treatment programs | Can be persistent in some patients |
| Gallbladder disease | Recognized risk in product labeling | Rapid weight loss may also contribute to gallstone risk |
| Pancreatitis | Important warning/clinical consideration | Persistent severe abdominal symptoms require medical evaluation |
| Volume depletion / acute kidney injury | Can occur particularly with severe GI symptoms | Dehydration can place additional stress on kidney function |
Thyroid C-cell tumor warning
Semaglutide-containing Wegovy products carry a boxed warning concerning thyroid C-cell tumors based on findings in rodents. The human relevance of those findings is unknown. Wegovy is contraindicated in people with a personal or family history of medullary thyroid carcinoma or with multiple endocrine neoplasia syndrome type 2.
This should not be rewritten as “semaglutide is proven to cause thyroid cancer in humans.” Those are different statements.
FDA-approved Wegovy prescribing information
Suicidal ideation and behavior: the 2026 correction
This is an important update because older internet articles may now be outdated. On January 13, 2026, the FDA stated that its comprehensive evaluation did not identify an increased risk of suicidal ideation or behavior with GLP-1 receptor agonist medicines and requested removal of that warning from the labels of affected products.
FDA's evaluation included a meta-analysis of 91 placebo-controlled GLP-1 trials involving more than 107,000 participants as well as a large retrospective cohort analysis.
Patients who develop new or worsening psychiatric symptoms should still discuss them with a healthcare professional; removal of the warning does not mean that every possible psychiatric symptom is impossible.
FDA: January 2026 GLP-1 safety review
Unapproved and compounded GLP-1 products
FDA distinguishes approved medicines from unapproved products. Compounded medicines are not FDA-approved and are not reviewed by FDA for safety, effectiveness and quality before marketing.
The FDA specifically warns that retatrutide and cagrilintide are not components of FDA-approved drugs and cannot be used in compounding under federal law.
Chapter 15 Muscle, Nutrition and Treatment Quality
Major weight loss generally includes reductions in both fat mass and lean mass. That does not automatically prove that a medication is directly “destroying muscle.” The more useful question is whether patients preserve sufficient muscle strength, physical function and nutritional adequacy during treatment.
A practical GLP-1 treatment framework
Effective obesity treatment should not be reduced to the number on the scale. A broader strategy may include:
- Adequate protein intake appropriate to the individual's circumstances.
- Resistance training and physical activity where medically appropriate.
- Monitoring nutritional quality during periods of markedly reduced appetite.
- Attention to hydration and gastrointestinal tolerance.
- Monitoring of cardiovascular, metabolic and other disease-specific outcomes.
GLP-1 therapy can substantially reduce appetite and total food intake. In some people, especially those with significant nausea, vomiting or very restrictive diets, that can make it harder to meet nutritional needs.
The goal should be high-quality weight loss—not simply maximum weight loss.
Chapter 16 GLP-1 Drugs, Cancer and Brain Research
Are GLP-1 drugs anti-cancer drugs?
Not at present.
GLP-1 medicines are being studied in relation to cancer because obesity, insulin resistance, inflammation and metabolic dysfunction are associated with multiple cancers. Better metabolic health may plausibly influence cancer risk indirectly, but that does not establish that semaglutide, tirzepatide or another GLP-1 medicine treats cancer.
Prevention, disease progression and cancer treatment are different questions and require different evidence.
GLP-1 and the brain
Appetite regulation is partly mediated through the brain, which is one reason GLP-1 therapies can change hunger, satiety and food intake.
Analyses of large outcome trials and observational cohorts associate GLP-1 receptor agonists with reduced risks of cognitive impairment and dementia, particularly in people with diabetes or cardiometabolic disease. However, randomized trials in established neurodegenerative disease have not shown clear clinical benefit.
The EVOKE and EVOKE+ phase 3 trials of oral semaglutide in people with mild cognitive impairment or early Alzheimer’s disease (thousands of participants, ~2 years) did not slow dementia progression in a clinically meaningful way, even when some biomarker changes occurred. A central open question is whether any effects are direct (on neural circuits expressing GLP-1 receptors in hippocampus, cortex, reward areas, etc.) or indirect (via better cardiometabolic health, reduced inflammation, vascular improvements). Receptor expression alone does not prove pharmacologically relevant brain exposure or causal target engagement.
Emerging multi-receptor approaches (engaging GIP, glucagon, or amylin pathways) may help clarify mechanisms. Ongoing studies (including acute cognitive testing in people with and without obesity) are addressing this.
Practical takeaway: Promising observational signals exist for risk reduction in metabolic populations, but these drugs are not established treatments for Alzheimer’s disease or cognitive impairment based on current randomized evidence.
Related: GLP-1 and Beyond: What the Evidence Shows on Brain Health, Cancer Risk, Addiction and Next-Generation Drugs - Science Special Issue (2026)Chapter 17 The Master GLP-1 Evidence Map
This table is the quickest way to understand what each landmark study actually contributes to the evidence base.
| Study | Therapy | Population / question | Main finding | Evidence |
|---|---|---|---|---|
| STEP-1 | Semaglutide | Obesity/overweight without diabetes | ~14.9% mean weight loss at 68 weeks | E5 |
| SELECT | Semaglutide | Obesity/overweight + cardiovascular disease, no diabetes | Reduced major cardiovascular events | E5 |
| SURMOUNT-1 | Tirzepatide | Obesity/overweight without diabetes | Large dose-dependent weight reduction | E5 |
| SURMOUNT-5 | Tirzepatide vs semaglutide | Obesity without diabetes | −20.2% vs −13.7% mean weight change | E5 |
| STEP-1 extension | Semaglutide withdrawal | Weight maintenance after stopping treatment | Substantial weight regain after withdrawal | E4 |
| SURMOUNT-4 | Tirzepatide | Weight maintenance after initial weight loss | Withdrawal led to substantial regain | E5 |
| FLOW | Semaglutide | Type 2 diabetes + CKD | Reduced major kidney and cardiovascular outcomes | E5 |
| STEP-HFpEF | Semaglutide | Obesity + HFpEF | Improved symptoms, function and weight | E5 |
| SUMMIT | Tirzepatide | Obesity + HFpEF | Reduced composite of CV death or worsening HF | E5 |
| SURMOUNT-OSA | Tirzepatide | Obesity + moderate/severe OSA | Reduced AHI and improved disease-related measures | E5 |
| ESSENCE | Semaglutide | MASH + F2/F3 fibrosis | Histologic improvement in MASH/fibrosis endpoints | E5 |
| OASIS 4 | Oral semaglutide | Overweight/obesity without diabetes | Substantial weight loss with daily oral therapy | E5 |
| ATTAIN-1 | Orforglipron | Obesity | Clinically meaningful weight reduction vs placebo | E5 |
| TRIUMPH-1 | Retatrutide | Obesity without diabetes | ~28.3% mean weight loss at 80 weeks at 12 mg | E4–E5* |
| TRIUMPH-2 | Retatrutide | Obesity + type 2 diabetes | Up to ~20.8% mean weight loss at 80 weeks | E4–E5* |
| TRIUMPH-3 | Retatrutide | Severe obesity + cardiovascular disease | Up to ~22.6% mean weight loss at 80 weeks | E4–E5* |
| REIMAGINE 5 | CagriSema | Type 2 diabetes | 12.4% vs 9.1% at week 60 in reported comparison | E4* |
| REDEFINE 9 | CagriSema | Overweight/obesity | ~21% weight loss at 68 weeks vs placebo | E4* |
*For retatrutide and the September 2026 CagriSema update, the cited results include company-reported topline data and/or investigational evidence that should be interpreted differently from fully published, independently scrutinized outcome trials.
The critical lesson
Cross-trial numbers should not be treated as an instant universal league table. A trial of semaglutide in cardiovascular disease is answering a different question from a tirzepatide obesity trial. A Phase 3 investigational study cannot be treated as equivalent to a drug with years of post-approval experience.
Compare medicines by asking: Which molecule? Which patient? Which dose? Which indication? Which endpoint? Which duration? Which safety trade-offs?
Chapter 18 What We Know, What We Don't Know and What Comes Next
What the evidence now supports
This is among the strongest conclusions in the modern obesity literature.
SELECT is the clearest obesity-specific cardiovascular outcome trial to date.
FLOW provides clinically meaningful renal outcome evidence for that population.
SURMOUNT-5 directly demonstrated greater mean weight loss than semaglutide under the studied conditions.
Withdrawal studies show substantial weight regain after stopping semaglutide or tirzepatide.
Wegovy tablets and Foundayo have changed the route-of-administration landscape.
Retatrutide and CagriSema illustrate two different strategies for pushing beyond conventional GLP-1 monotherapy.
What remains uncertain
Several questions are still open:
- How should treatment be optimized over decades rather than years?
- Which patients derive the greatest cardiovascular, kidney or liver benefit?
- How should clinicians best preserve muscle and physical function during major weight loss?
- What happens after treatment interruption many years into therapy?
- How will next-generation drugs compare head-to-head with current leading therapies?
- What are the consequences of long-term use in younger adults beginning treatment earlier in life?
- Which disease-specific indications will ultimately be supported by dedicated outcomes trials?
What OneDayMD is watching next
The next era of GLP-1 research is likely to shift away from simply demonstrating that patients can lose weight. The harder questions are about durability, organ protection, quality of weight loss, physical function, access, adherence and long-term outcomes.
Retatrutide's planned regulatory submission, additional head-to-head studies, cardiovascular and renal outcome trials, and the continuing CagriSema program will be particularly important.
Chapter 19: Frequently Asked Questions
Which GLP-1 drug has the strongest weight-loss evidence?
Several medicines have strong evidence, but cross-trial comparisons should be used cautiously. In SURMOUNT-5, tirzepatide produced greater mean weight loss than semaglutide in adults with obesity without type 2 diabetes. That result does not make the medications interchangeable or establish a universal treatment choice.
Does semaglutide reduce heart attack and stroke risk?
Yes, in the population studied in SELECT: adults with overweight or obesity and established cardiovascular disease without diabetes. The trial demonstrated a reduction in major cardiovascular events compared with placebo.
Does semaglutide protect the kidneys?
FLOW provides strong evidence of kidney and cardiovascular benefit in people with type 2 diabetes and chronic kidney disease. The result should not automatically be generalized to every GLP-1 user.
Is tirzepatide a GLP-1 drug?
Tirzepatide activates both the GIP and GLP-1 receptors. It is therefore more accurately described as a dual GIP/GLP-1 receptor agonist.
Is oral semaglutide approved for obesity?
Yes. Wegovy tablets are FDA-approved for weight management in eligible adults in the United States.
Is Foundayo the same thing as Wegovy?
No. Both are oral incretin-based obesity medicines, but their molecules are different. Wegovy tablets contain semaglutide; Foundayo contains orforglipron.
Is Wegovy HD a different drug?
No. Wegovy HD is a higher-dose formulation of semaglutide rather than a completely different molecule.
Is retatrutide approved?
No. As of September 23, 2026, retatrutide remains investigational. Lilly has announced plans to submit a BLA to FDA in Q1 2027.
Is CagriSema approved?
CagriSema remains investigational as of this update. September 2026 results are promising but were reported as topline company data.
Do GLP-1 drugs cause suicidal thoughts?
The FDA's January 2026 comprehensive review did not identify an increased risk of suicidal ideation or behavior with GLP-1 receptor agonists and requested removal of the warning from affected labeling.
Do GLP-1 drugs cause muscle loss?
Weight loss commonly includes some reduction in lean mass. That fact alone does not establish direct drug-induced muscle damage. Protein intake, resistance exercise, physical function and total nutritional adequacy are important parts of evaluating the quality of weight loss.
Are GLP-1 drugs anti-aging drugs?
There is significant interest in longevity and healthy-aging research, but anti-aging is not an established primary indication for GLP-1 medicines. Better cardiometabolic health may produce downstream benefits, but claims should be distinguished from direct evidence of lifespan extension.
Are GLP-1 drugs cancer treatments?
No. Current evidence does not establish semaglutide, tirzepatide or other GLP-1 medicines as standard anti-cancer treatments.
Key Studies and Primary Sources
The following primary or high-authority sources are the foundation of this master guide:
- STEP-1 — Once-Weekly Semaglutide in Adults with Overweight or Obesity
- SELECT — Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes
- SURMOUNT-1 — Tirzepatide in obesity
- SURMOUNT-5 — Tirzepatide versus Semaglutide
- STEP-1 extension — Weight regain after semaglutide withdrawal
- SURMOUNT-4 — Tirzepatide maintenance and withdrawal
- FLOW — Semaglutide and chronic kidney disease
- STEP-HFpEF — Semaglutide in obesity-related HFpEF
- SUMMIT — Tirzepatide in HFpEF with obesity
- SURMOUNT-OSA — Tirzepatide in obstructive sleep apnea and obesity
- ESSENCE — Phase 3 semaglutide trial in MASH
- OASIS 4 — Oral semaglutide 25 mg
- ATTAIN-1 — Orforglipron
- FDA — Foundayo (orforglipron) approval
- FDA — Wegovy HD 7.2 mg approval
- FDA — January 2026 GLP-1 suicidal ideation safety review
- FDA — Concerns with unapproved GLP-1 drugs
- Lilly — TRIUMPH-1 retatrutide Phase 3 topline results
- Lilly — TRIUMPH-2 and TRIUMPH-3
- Novo Nordisk — September 2026 CagriSema data
GLP-1 Knowledge graph: Explore the OneDayMD GLP-1 research hub
Tools and Telehealth (Affiliate Links)
- Virtual care: if you need a clinician to review your symptoms, labs or GLP-1 plan, The Wellness Company virtual care is one telehealth pathway. Availability, eligibility and prescribing decisions are determined by their licensed clinicians.
- Strength training at home: resistance band sets support the resistance-training advice above.
- Portion and protein tracking: a digital kitchen scale makes it easier to estimate protein per meal.
Weight Loss & Metabolic Health Collection (E-Store)
- Tirzepatide — oral Rx GLP-1/GIP weight loss solution
- APPETITE — natural GLP-1/GLP-2 appetite suppressant with Akkermansia
- PEAK METABOLISM — Berberine + Curcumin, natural metabolism boost
- Bioavailable Berberine — "Nature's Ozempic" — blood sugar & insulin sensitiser
- → Full Weight Management Collection (TWC)
Medical Disclaimer
This page is for educational and informational purposes only and does not constitute medical advice, diagnosis or treatment. GLP-1 medicines are prescription drugs with specific indications, contraindications, warnings, dosing requirements and monitoring considerations. Treatment decisions should be made with a qualified healthcare professional who understands the individual's medical history, medications, laboratory findings and treatment goals.
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