Peptides for weight loss: what is approved, what is not, and what works

Two peptides have the evidence people are hoping for: semaglutide (Wegovy) and tirzepatide (Zepbound), both FDA-approved, both backed by large phase 3 trials. A newer group, led by retatrutide and CagriSema, has strong trial data but no approval. The peptides that fill social media feeds and online shops, such as AOD-9604 and MOTS-c, are in a third group: not approved, with no trial showing weight loss in people. Those three groups are very different things, even though all get called “peptides.” The GLP-1 section covers the approved drugs in depth, and the peptides A-Z covers the rest. This is an overview by evidence, not a ranking.

The three groups at a glance

Each group sits on a different rung of the evidence ladder. A human trial tells you far more than a mouse study, and an FDA label tells you more than either, because it comes with an agency review of safety data and a list of who should not take the drug.

Which peptides are FDA-approved for weight loss?

Semaglutide (Wegovy), tirzepatide (Zepbound) and liraglutide (Saxenda) are the peptides approved for chronic weight management in the broad population with obesity. People hoping to get “a peptide for weight loss” usually mean one of these, whether they know it or not. Each is used with a reduced-calorie diet and more physical activity.

Here is what the labels and main trials report. The drugs are listed by brand name, not by how good they are.

Saxenda (liraglutide) is a daily injection, also approved for teens 12 and older. Wegovy’s label covers teens too, and it adds a use beyond weight: lowering the risk of heart attack, stroke and cardiovascular death in adults with heart disease and obesity or overweight. That came from SELECT, a trial of 17,604 adults. Foundayo earns a place in this table although it is not a peptide, because it works on the same receptor and people weigh it against the others.

Other FDA-approved weight drugs are not peptides at all: orlistat, phentermine-topiramate and naltrexone-bupropion. A daily injection, setmelanotide (Imcivree), is limited to specific rare genetic causes of obesity confirmed by testing. Older drugs such as phentermine alone are approved only for a few weeks.

How do these drugs cause weight loss?

They copy hormones your gut releases after eating. GLP-1 (glucagon-like peptide-1) tells the brain you are full, slows the stomach, and helps the pancreas release insulin when blood sugar is high. Tirzepatide also acts on a second hormone receptor, GIP. The result is a smaller appetite, and that is why the weight change takes months.

Who qualifies, and what can you expect?

The National Institute of Diabetes and Digestive and Kidney Diseases describes the usual threshold as an adult with a BMI of 30 or more, or 27 or more with a weight-related problem such as high blood pressure or type 2 diabetes. Those trial averages took 64 to 72 weeks, and individual results vary widely around them. Doses rise slowly over months, which is why early weight loss is modest; the tirzepatide dosage chart and semaglutide dosage chart show the label ladders. NIDDK says that if you have not lost at least 5% of your starting weight after 12 weeks on the full dose, your clinician will probably suggest stopping or changing course. Even a 5% to 10% loss can improve blood sugar, blood pressure and triglycerides.

What are the risks of the approved drugs?

Stomach side effects are the most common problem. On the Zepbound label, nausea affected 25% to 29% of people versus 8% on placebo. On Wegovy 2.4 mg it was 44% versus 16%. Most of it happened during dose increases and eased with time.

The serious warnings matter more:

• Boxed warning. Wegovy and Zepbound both carry a boxed warning about thyroid C-cell tumors, seen in rodents. Human relevance is unknown. Neither may be used by anyone with a personal or family history of medullary thyroid carcinoma or with Multiple Endocrine Neoplasia syndrome type 2.
• Other label warnings. Pancreatitis, gallbladder disease, kidney injury from dehydration, low blood sugar with insulin or a sulfonylurea, serious allergic reactions, diabetic eye complications and food entering the lungs under anesthesia.
• Pregnancy. NIDDK says weight-loss medications should not be taken during pregnancy or when planning one, and are not recommended while breastfeeding.
• Not to be combined. The Wegovy and Zepbound labels both say not to use them with another GLP-1 drug.

Severe stomach pain that will not go away, sometimes reaching the back, is the classic sign of pancreatitis, and the labels say to stop and call right away. Swelling of the face or throat, or trouble breathing, needs emergency care. The tirzepatide side effects guide and semaglutide side effects guide have the full tables.

What happens when you stop?

Most people regain weight. In the STEP 1 extension, people who had lost 17.3% on semaglutide regained 11.6 percentage points within a year of stopping. In SURMOUNT-4, everyone took tirzepatide for 36 weeks. Those then switched to placebo regained 14.0% over a year, while those who continued lost another 5.5%. NIDDK describes obesity as a chronic disease, and the trials behave that way: the effect lasts about as long as the treatment does.

What are investigational peptides for weight loss?

These are real drug candidates with serious trial data, but no approved product and no approved dose.

“Investigational” means something specific. These drugs cannot be bought or prescribed normally, and they are given inside clinical trials. Lilly also runs a narrow compassionate use program for retatrutide, which physicians apply to, for adults with refractory obesity and two or more serious complications who cannot join a trial. Anything sold online is not that program. The FDA says retatrutide and cagrilintide “cannot be used in compounding under federal law.” The October 2026 HHS peptide policy described below does not change any of that; investigational drugs are unaffected.

The FDA has warned companies selling retatrutide, survodutide and mazdutide falsely labeled “for research purposes.” A vial with one of these names on it is not the drug tested in the trials. If you are interested, the honest route is ClinicalTrials.gov, where you can search a drug’s name with the status filter set to “Recruiting.”

Do AOD-9604 and MOTS-c work for weight loss?

No human trial has shown that either one causes weight loss.

AOD-9604 is the more instructive story, because it was actually tested. It was developed as an obesity pill, the trials did not support it, and the developer abandoned it in 2007. It now sells as a “fat-burning” injection, a route no human study has tested.

MOTS-c is earlier still. The human data closest to it come from CB4211, a different, modified molecule, where a 4-week study in 20 people with obesity and fatty liver showed only a downward trend in weight. A phase 2a trial of MOTS-c itself (NCT07505745) began enrolling in 2026 and has no results.

What the October 2026 HHS policy means for MOTS-c

As of November 2, 2026, an interim HHS policy says HHS does not intend to take enforcement action against a state-licensed pharmacy, federal facility or licensed physician compounding MOTS-c acetate for injection under the skin or into muscle, if ten conditions are met, until a final rule decides whether MOTS-c goes on the 503A bulks list. Those conditions include a single active ingredient, a valid patient-specific prescription and sourcing from an FDA-registered facility.

That is a choice not to enforce, and it stops well short of approval. MOTS-c is not FDA-approved and not on the bulks list, no rule has been proposed, and FDA has not reviewed any compounded product for safety, effectiveness or quality. The notice says the policy “does not establish any rights for any person and is not binding on HHS or the public.” It covers 503A compounding only, states can be stricter, HHS may revisit it, and comments are open until November 13, 2026. The evidence has not changed: a policy about enforcement is not evidence that a peptide works or is safe.

AOD-9604 is not on the HHS list, so the policy does not cover it. CJC-1295 and ipamorelin are not on the list either. Tesamorelin (Egrifta) is a real approved drug, but only for excess belly fat in people with HIV-related lipodystrophy, and its label says it is not for weight loss.

Where compounded semaglutide and tirzepatide fit

Compounded versions sit awkwardly between these groups. They use the names of approved drugs, but the compounded product itself is not FDA-approved or reviewed for safety, effectiveness or quality. The FDA says compounded drugs should be used only when a patient’s medical needs cannot be met by an approved drug. The official shortages of both drugs have ended. By May 31, 2026 the FDA had received 990 adverse event reports for compounded semaglutide and more than 730 for compounded tirzepatide, and it has warned about dosing errors, some requiring hospitalization. The compounded semaglutide guide and compounded tirzepatide guide cover the rules.

The third kind of product is the one to steer clear of. Products sold “for research use only” are not legal to use on people, whatever peptide is named on the vial, and HHS says its interim policy is meant to discourage their use. The FDA urges consumers not to purchase these products, which it describes as “of unknown quality.”

What to do instead of buying a vial online

If weight is affecting your health, the useful next steps are ordinary ones.

• Check whether you qualify. BMI of 30 or more, or 27 or more with a weight-related condition, is the usual starting point.
• See a licensed prescriber, in person or through telehealth, and bring a list of everything you take, including supplements.
• Ask about cost early. Coverage varies by plan, and manufacturers run self-pay programs. The cheapest GLP-1 without insurance guide compares them.
• Use a lifestyle program alongside any drug. NIDDK says medications work best combined with one, and they do not replace healthy eating and activity.
• Ask about surgery if your BMI is high. A clinician can refer you to a bariatric surgeon when medication is not enough.
• Look at trials if you want to help test something new.

Questions worth bringing to the appointment:

• Which approved drug fits my health history, and why?
• What should I expect by 12 weeks on the full dose, and when would we change course?
• How long would I stay on it, and what is the plan if I stop?
• Do any of my medicines interact, or does my family history rule anything out?

The goals overview sets weight loss beside the other outcomes people ask about, and the FDA status tracker records each approval and rule as it happens.