Which Peptides Work for Weight Loss?

Search for peptides for weight loss and you will find long lists of compounds, blends and stacks, many of them promising to melt fat or speed up your metabolism. Most of these lists treat every peptide as if it had the same evidence behind it.

They do not. A small number of peptide medicines have been tested in large clinical trials involving thousands of people with obesity and are approved by the FDA for weight management. Most of the others have never been tested that way. Knowing the difference is the most useful thing to understand before considering any treatment.

Why the strongest weight loss medicines are peptides

After a meal, your gut releases hormones that tell the brain you have eaten enough and help the body handle the sugar from that meal. One of the most important is GLP-1, which is itself a peptide. The medicines with the strongest evidence for weight loss are modified versions of these gut hormones, designed to last far longer in the body than the natural signal, which is broken down within minutes.

Liraglutide, semaglutide and tirzepatide all work this way. Liraglutide and semaglutide act on the GLP-1 receptor, while tirzepatide acts on both the GLP-1 receptor and the receptor for a second gut hormone, GIP. In practice, they reduce appetite, slow down how quickly the stomach empties so that a meal feels more filling, and improve how the body manages blood sugar. If you have wondered why these medicines are usually given as injections, our guide to what peptides are and how they work explains it.

What the trials show

Each of these three medicines was tested against a placebo in adults with obesity, or with overweight and a weight-related health condition, and everyone in these trials also received advice on diet and exercise. The comparison with placebo is what matters, because it shows how much the medicine added on top of lifestyle changes.

Liraglutide came first. In the SCALE trial, adults taking it once a day lost 8.0% of their body weight on average over 56 weeks, compared with 2.6% on placebo. Semaglutide, taken once a week, went further. In STEP 1, average weight loss was 14.9% over 68 weeks, against 2.4% with placebo. In SURMOUNT-1, adults on the highest dose of tirzepatide lost 20.9% over 72 weeks, compared with 3.1% on placebo. When the two newer medicines were compared directly in SURMOUNT-5, tirzepatide produced greater average weight loss than semaglutide, 20.2% against 13.7%.

Semaglutide is now also available as a daily tablet. The FDA approved a 25 mg tablet for weight management in December 2025, after the OASIS 4 trial found average weight loss of 13.6% over 64 weeks, compared with 2.2% on placebo.

These figures are averages. In every trial, some people lost much more and some much less, which is why a clinician looks at your health, your goals and how you tolerate treatment before recommending one medicine over another.

What about other peptides sold for fat loss?

The list of peptides approved for weight management is short. Apart from the medicines above, the only other one is setmelanotide, which is used for a few rare conditions that disrupt the brain’s appetite signals, such as certain inherited disorders, and not for common obesity.

Many of the other peptides that appear on online lists have not been through trials like SCALE, STEP or SURMOUNT. Some have only been studied in animals or in small early studies, and some are sold as blends whose combined effect has never been tested. That does not prove they cannot work, but it does mean nobody can say how well they work, at what dose, or with what risks.

Who these medicines are for, and what to expect

GLP-1 medicines are approved for adults with obesity, and for adults with overweight who also have at least one weight-related condition, such as high blood pressure or type 2 diabetes. The trials above enrolled adults with a body mass index of 30 or more, or 27 or more with a weight-related condition.

The most common side effects are digestive: nausea, diarrhea, vomiting and constipation. In the trials, these were usually mild to moderate and eased over time, and doses were increased gradually over several months to help the body adjust. Semaglutide carries a boxed warning because it caused thyroid tumors in rodents. It is not known whether it does the same in people, but it is not used in anyone with a personal or family history of medullary thyroid cancer or with multiple endocrine neoplasia type 2.

It also helps to plan for the long term from the start. In the STEP 1 extension, people who stopped semaglutide regained about two thirds of the weight they had lost within a year. Whether to continue, reduce or stop treatment is something to decide with your clinician, together with the eating and activity habits that help keep weight off. Our article on medical weight loss versus dieting covers this in more detail.

Weight loss treatment at SaltMD

At SaltMD, weight loss treatment starts with a consultation with a licensed clinician, in person in Atlanta or by video. Your clinician reviews your health history and goals, and if lab work would help, blood can be drawn at a lab near you or at our office, or recent results can be reviewed. If a GLP-1 medicine is right for you, your clinician will explain which one, in what form and why, and your prescription is filled by a partner pharmacy and shipped to you. Regular check-ins follow, to manage side effects and adjust the dose as you progress.

Learn more about our medical weight loss program, semaglutide and peptide therapy.

Sources

• Pi-Sunyer X, Astrup A, Fujioka K, et al. A randomized, controlled trial of 3.0 mg of liraglutide in weight management. N Engl J Med. 2015;373(1):11-22.
• Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity. N Engl J Med. 2021;384(11):989-1002. doi:10.1056/NEJMoa2032183
• Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity. N Engl J Med. 2022;387(3):205-216. doi:10.1056/NEJMoa2206038
• Aronne LJ, Horn DB, le Roux CW, et al. Tirzepatide as compared with semaglutide for the treatment of obesity. N Engl J Med. 2025;393(1):26-36. doi:10.1056/NEJMoa2416394
• Wharton S, et al. Oral semaglutide at a dose of 25 mg in adults with overweight or obesity. N Engl J Med. 2025. doi:10.1056/NEJMoa2500969
• Wilding JPH, Batterham RL, Davies M, et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extension. Diabetes Obes Metab. 2022;24(8):1553-1564. doi:10.1111/dom.14725
• Lau J, Bloch P, Schäffer L, et al. Discovery of the once-weekly glucagon-like peptide-1 (GLP-1) analogue semaglutide. J Med Chem. 2015;58(18):7370-7380. doi:10.1021/acs.jmedchem.5b00726
• WEGOVY (semaglutide) injection and tablets, prescribing information. Novo Nordisk. Revised 2026.
• Imcivree (setmelanotide) FDA approval history. Drugs.com.

This article is for general education and is not medical advice.