GLP-1s: What the Evidence Actually Shows

GLP-1 is a hormone released from the gut after eating. It helps regulate glucose-dependent insulin release, glucagon, gastric emptying, appetite, and food intake. GLP-1 receptor agonists are medicines designed to act at that receptor for longer than the native signal. ^{[4, 6]}

Tirzepatide is often discussed with GLP-1 receptor agonists, but its FDA labels identify it as a dual GIP and GLP-1 receptor agonist. That distinction matters when comparing mechanisms and evidence. ^{[5, 7]}

Product names are not interchangeable shorthand. Wegovy and Ozempic contain semaglutide but have different labeled uses; Zepbound and Mounjaro contain tirzepatide but likewise have different labeled uses. Approval follows the product-specific evidence and labeling. ^{[4, 6, 5, 7]}

As of the evidence cutoff, labeled uses across these products include glycemic control in defined people with type 2 diabetes, reduction of specified cardiovascular or kidney risks in defined high-risk populations, long-term weight management in defined populations, moderate-to-severe obstructive sleep apnea in adults with obesity, and a Wegovy indication for noncirrhotic MASH with moderate-to-advanced fibrosis. The exact label sets the boundary. ^{[4, 6, 5, 7]}

Context: The Wegovy MASH indication uses accelerated approval and may depend on confirmatory evidence, as its label explains.

Interest is not based only on scale weight. Product-specific trials have evaluated glycemic outcomes, body weight, cardiovascular events, kidney outcomes, liver-disease markers, and sleep-apnea severity. A result in one domain or population does not establish every other claim. ^{[4, 6, 5, 10, 12]}

Large average changes can coexist with wide individual variation, side effects, treatment discontinuation, and weight regain after treatment changes. Trial averages are not individual predictions. ^{[9, 11]}

These medicines are studied as part of ongoing care, usually alongside nutrition and physical-activity interventions. A trial does not answer every question about access, adherence, lean mass, long-term maintenance, or what happens after a person stops treatment. ^{[9, 11, 4]}

STEP 1 randomized 1,961 adults with overweight or obesity and without diabetes to semaglutide or placebo, both with lifestyle intervention, for 68 weeks. Mean body-weight change was −14.9% with semaglutide and −2.4% with placebo. Gastrointestinal events led to discontinuation in 4.5% and 0.8%, respectively. ^[9]

Context: This was a defined trial population and product—not a guarantee of weight change for an individual or evidence for a compounded version.

SELECT randomized 17,604 adults with overweight or obesity, established cardiovascular disease, and no diabetes. A major cardiovascular event occurred in 6.5% of the semaglutide group and 8.0% of the placebo group; the hazard ratio was 0.80. Adverse events leading to permanent discontinuation occurred in 16.6% and 8.2%, respectively. ^[10]

Context: The cardiovascular result applies to the studied high-risk population and product.

SURMOUNT-1 randomized 2,539 adults with obesity or overweight and without diabetes for 72 weeks. Mean body-weight changes across the three tirzepatide arms were −15.0%, −19.5%, and −20.9%, compared with −3.1% for placebo. Adverse-event discontinuation was 4.3%, 7.1%, and 6.2% across those arms and 2.6% with placebo. ^[11]

Context: These are trial averages, not individual predictions, and do not demonstrate equivalence for a compounded product.

SURMOUNT-OSA comprised two randomized trials with 469 adults who had obesity and moderate-to-severe obstructive sleep apnea. After 52 weeks, tirzepatide reduced the apnea–hypopnea index more than placebo in both the group not using positive-airway-pressure therapy and the group continuing that therapy. ^{[12, 5]}

Context: The trials address a defined sleep-apnea population; they are not evidence for general sleep improvement.

Percent changes across separate trials should not be ranked as though the studies were head-to-head. Populations, products, protocols, estimands, follow-up, and handling of missing data differ. ^{[9, 11]}

For approved GLP-1–based medicines, clinical decisions can draw on large human trials and product labels. Cell and animal mechanisms can add context, but they should not displace observed human benefits, harms, or product-specific evidence. ^{[10, 4, 5]}

Both current Wegovy and Zepbound labels carry boxed warnings because semaglutide and tirzepatide caused thyroid C-cell tumors in rodents. The labels state that the relevance to humans is unknown and contraindicate use in people with a personal or family history of medullary thyroid carcinoma or MEN 2. ^{[4, 5]}

Context: The correct statement preserves both parts: a serious labeled warning and unresolved human relevance.

Gastrointestinal effects—including nausea, diarrhea, vomiting, constipation, abdominal symptoms, and dyspepsia—are among the most common labeled adverse reactions. Severe gastrointestinal reactions can occur, and both labels caution against use in severe gastroparesis. ^{[4, 5]}

Current labels also address pancreatitis, gallbladder disease, acute kidney injury related to volume depletion, serious hypersensitivity, hypoglycemia risk with some diabetes medicines, diabetic-retinopathy considerations, and pulmonary aspiration during anesthesia or deep sedation. ^{[4, 5, 6, 7]}

These medicines delay gastric emptying and can affect absorption of oral medicines. Tirzepatide labeling also includes a specific contraception precaution after treatment initiation or escalation. Medication review is therefore part of product-specific risk assessment. ^{[4, 5, 7]}

Weight-loss use is not compatible with pregnancy under current labeling, and the labels contain product-specific pregnancy and reproductive-potential instructions. This guide intentionally does not reproduce administration schedules. ^{[4, 5]}

In January 2026, FDA reported that its comprehensive review did not identify an increased risk of suicidal ideation or behavior with GLP-1 receptor agonists and requested removal of that warning from affected labels. Updated Wegovy and Zepbound labels record its removal. ^{[8, 4, 5]}

FDA-approved drugs undergo product-specific premarket review. Compounded and other unapproved GLP-1 versions do not undergo FDA premarket review for safety, effectiveness, or quality, even when an ingredient name resembles an approved medicine. ^[1]

FDA says semaglutide sodium and semaglutide acetate are different active ingredients from the semaglutide used in approved drugs. The agency says it lacks information showing that those salt forms have the same chemical and pharmacologic properties and is unaware of a lawful basis for their use in compounding. ^[1]

FDA has described dosing errors, fraudulent labels, shipping and storage concerns, and adverse-event reports involving compounded semaglutide and tirzepatide. Passive adverse-event reports cannot provide incidence rates or prove causation; underreporting is also likely because many state-licensed pharmacies are not required to submit reports to FDA. ^[1]

As of May 31, 2026, FDA reported receiving 990 adverse-event reports associated with compounded semaglutide and more than 730 associated with compounded tirzepatide. FDA also cautioned that causation may not be determinable and that the counts are likely incomplete. ^[1]

Context: These are surveillance counts, not denominated risk estimates and not proof that every report was caused by the product.

FDA's April 2026 policy update said semaglutide and tirzepatide were not on the 503B bulks list or FDA drug-shortage list and restated limits on making products that are essentially copies. Section 503A and 503B operate under different conditions; neither is an approval pathway for the compounded drug. ^[2]

On April 30, 2026, FDA proposed excluding semaglutide, tirzepatide, and liraglutide from the 503B bulks list after finding no clinical need for outsourcing facilities to compound them from bulk substances. FDA called it a proposal, not a final determination, and said it would consider public comments. ^[3]

Which exact product and labeled use are being considered, and does the person's diagnosis and risk profile match the population in the supporting evidence? ^{[4, 6, 5, 7]}

What outcome matters—glycemic control, weight, cardiovascular risk, kidney risk, sleep apnea, or another goal—and what is the absolute evidence for that specific outcome? ^{[10, 12, 6]}

Which contraindications, gastrointestinal history, gallbladder or pancreatic history, kidney risks, eye disease, pregnancy considerations, procedures, and interacting medicines change the balance for this person? ^{[4, 5]}

If the product is compounded or otherwise unapproved, what evidence establishes its exact active ingredient, identity, quality, sterility, storage, and clinical equivalence? An approved-product trial cannot answer those questions for it. ^[1]

What is the long-term plan for monitoring, nutrition, physical activity, side effects, access, adherence, and treatment changes? What remains uncertain for this individual's priorities? ^{[4, 9, 11]}