Peptides for Weight Loss: GLP-1 Medicines, Trial Results and the Research Pipeline

Peptides for weight loss have gone from a niche research topic to some of the most prescribed medicines in the world in just a few years. The best-known examples, semaglutide and tirzepatide, are peptides modeled on hormones made in the gut. Alongside them sits a long list of experimental compounds sold online with far weaker evidence. This guide explains how weight-loss peptides work, which ones are approved, what the clinical trials found, which are still in development, and the risks the FDA has flagged with unapproved products.

Quick answer: The peptides with proven weight-loss effects are prescription GLP-1-based medicines. In large trials, semaglutide (Wegovy) produced an average 14.9% loss of body weight over 68 weeks and tirzepatide (Zepbound) up to 20.9% over 72 weeks, compared with 2.4% and 3.1% on placebo. Newer peptides such as retatrutide are still in clinical trials, and compounds like AOD-9604 have not become approved medicines. Unapproved and "research use only" versions are not checked by the FDA for safety, quality or dosing.

How peptides for weight loss work

Most weight-loss peptides copy hormones that the gut and pancreas release after a meal. These hormones act on the brain, stomach and pancreas to control appetite and blood sugar:

• GLP-1 (glucagon-like peptide-1): reduces appetite, slows stomach emptying and increases insulin release when blood sugar is high. Semaglutide and liraglutide activate the GLP-1 receptor.
• GIP (glucose-dependent insulinotropic polypeptide): another gut hormone involved in insulin release and energy balance. Tirzepatide activates both GIP and GLP-1 receptors.
• Glucagon: raises energy expenditure and affects how the liver handles fat. Retatrutide, survodutide and mazdutide add glucagon-receptor activity.
• Amylin: released with insulin from the pancreas, it promotes fullness and slows stomach emptying. Cagrilintide and eloralintide are amylin analogues.

Natural GLP-1 lasts only minutes in the bloodstream. Medicines such as semaglutide are modified so they last about a week, which is what makes once-weekly injections possible.

FDA-approved peptides for weight loss

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) lists the medicines approved for long-term weight management. Three of them are peptides:

These medicines are approved for adults with obesity, or with overweight and at least one weight-related condition, alongside a reduced-calorie diet and increased physical activity. Semaglutide and liraglutide are also approved for some adolescents aged 12 and over.

Semaglutide

In the STEP 1 trial published in the New England Journal of Medicine, 1,961 adults without diabetes took weekly semaglutide or a placebo for 68 weeks, with lifestyle support. Average weight loss was 14.9% with semaglutide and 2.4% with placebo, and half of the semaglutide group lost 15% or more of their body weight. Nausea and diarrhea were the most common side effects, usually mild to moderate and temporary. Novo Nordisk announced FDA approval of an oral Wegovy pill on December 22, 2025, the first oral GLP-1 medicine approved for weight management.

Tirzepatide

In the SURMOUNT-1 trial, 2,539 adults with obesity or overweight took weekly tirzepatide at one of three doses or a placebo for 72 weeks. Average weight loss was 15.0%, 19.5% and 20.9% across the three doses, compared with 3.1% on placebo, and more than half of participants on the two higher doses lost at least 20% of their body weight. The FDA approved tirzepatide as Zepbound for chronic weight management on November 8, 2023.

A note on orforglipron

On April 1, 2026, the FDA approved orforglipron (Foundayo), a once-daily pill for chronic weight management. It activates the GLP-1 receptor, but unlike the medicines above it is a small molecule, not a peptide, which is one reason it can be taken by mouth without the strict fasting rules that oral peptide medicines need.

Investigational weight-loss peptides

Several newer peptides are in clinical trials. None of the following is FDA-approved for weight management as of October 2026.

• Retatrutide: a triple agonist of the GIP, GLP-1 and glucagon receptors. In a 48-week phase 2 trial of 338 adults, average weight loss reached 24.2% at the highest dose, compared with 2.1% on placebo. Side effects were mainly gastrointestinal and dose-related, and heart rate rose with dose before declining. Phase 3 trials such as TRIUMPH-1 have since been completed, and in August 2026 Lilly reported that its data package for obesity was complete, with plans to submit an application to the FDA in the first quarter of 2027. See our retatrutide research listing.
• Cagrilintide: a long-acting amylin analogue, studied alone and in combination with semaglutide. See cagrilintide.
• Survodutide and mazdutide: dual agonists of the GLP-1 and glucagon receptors in clinical development. See survodutide and mazdutide.
• Eloralintide: an amylin-receptor agonist in clinical development. See eloralintide.

Phase 2 results are an early signal. Phase 3 trials, which are larger and longer, are what regulators rely on to judge whether a medicine is safe and effective enough to approve.

Other peptides marketed for weight loss

Many other peptides appear on "best peptides for weight loss" lists, usually with much weaker evidence.

• AOD-9604 and HGH Fragment 176-191: synthetic fragments of the end of the growth hormone molecule, studied for fat metabolism. AOD-9604 was developed as an obesity treatment but did not become an approved medicine. The FDA says it has identified serious adverse events that may be associated with AOD-9604, although causality is not clear, and WADA prohibits both fragments in sport. See HGH Fragment 176-191.
• Tesamorelin: a growth hormone-releasing hormone analogue approved only to reduce excess abdominal fat in people with HIV-associated lipodystrophy. Its label states it is not indicated for weight loss. Our guide to HGH peptides explains how it works.
• MOTS-c: a small peptide encoded in mitochondrial DNA and studied in metabolism research. The FDA reports that it has not identified human exposure data.

Risks of unapproved and research GLP-1 products

The popularity of GLP-1 medicines has created a large market for copies. The FDA's page on concerns with unapproved GLP-1 drugs used for weight loss makes several points:

• Unapproved versions do not undergo FDA review for safety, effectiveness and quality before they are marketed, and compounded drugs are not FDA-approved.
• Counterfeit products may contain the wrong ingredients.
• The FDA has warned companies selling unapproved drugs labeled "for research purposes" or "not for human consumption" that were sold directly to consumers for human use with dosing instructions.
• As of May 31, 2026, the FDA had received 990 reports of adverse events associated with compounded semaglutide and more than 730 associated with compounded tirzepatide, including hospitalizations that may be related to dosing errors.

Approved GLP-1 medicines also carry warnings. Their labels include a warning about thyroid C-cell tumors seen in rodent studies, and cautions about pancreatitis and gallbladder problems, which is one reason they are prescribed and monitored by clinicians.

Roids & Peps lists semaglutide, tirzepatide, retatrutide and related compounds in our metabolic research area strictly as laboratory research materials. They are not medicines, they are not sold for human use, and no dosing instructions are provided. Anyone considering medication for weight loss should speak with a licensed clinician about approved options. Researchers can check identity and purity data for each batch in our COA library.

Weight loss peptides and lifestyle

Even the most effective medicines work alongside diet and activity, not instead of them. NIDDK notes that weight management medicines do not replace physical activity or healthy eating, and that they work best when combined with a lifestyle program. In the semaglutide and tirzepatide trials above, participants in both the treatment and placebo groups received lifestyle counseling. Weight is often regained when treatment stops, which is why these medicines are approved for long-term use.

Frequently asked questions

What is the best peptide for weight loss?

Among approved medicines, tirzepatide produced the largest average weight loss in its main trial, up to 20.9% over 72 weeks, followed by semaglutide at 14.9% over 68 weeks. The right choice for an individual depends on their health and should be made with a clinician.

Is semaglutide a peptide?

Yes. Semaglutide is a modified version of the GLP-1 hormone, a peptide of 31 amino acids, with changes that let it last about a week in the body.

Is retatrutide approved?

No. As of October 2026, retatrutide has not been approved by the FDA for any use. Lilly has said it plans to submit an application for obesity in the first quarter of 2027.

Do research peptides for weight loss work?

Products sold "for research use only" are not approved medicines and have not been reviewed by the FDA for safety, quality or dosing. The FDA has warned about adverse events and dosing errors linked to unapproved GLP-1 products.

Is AOD-9604 effective for weight loss?

AOD-9604 was developed as an obesity treatment but did not become an approved medicine, and the FDA has noted possible serious adverse events. It is not an established weight-loss treatment.

Sources

• National Institute of Diabetes and Digestive and Kidney Diseases: Prescription medications to treat overweight and obesity
• Wilding JPH, et al. Once-weekly semaglutide in adults with overweight or obesity. N Engl J Med. 2021.
• Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity. N Engl J Med. 2022.
• Jastreboff AM, et al. Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial. N Engl J Med. 2023.
• U.S. Food and Drug Administration: FDA approves new medication for chronic weight management (Zepbound, 2023)
• U.S. Food and Drug Administration: FDA approves first new molecular entity under national priority voucher program (Foundayo, 2026)
• U.S. Food and Drug Administration: FDA's concerns with unapproved GLP-1 drugs used for weight loss
• Novo Nordisk: FDA approves oral Wegovy pill
• ClinicalTrials.gov: TRIUMPH-1, a study of retatrutide in participants who have obesity or overweight
• Eli Lilly and Company: Second-quarter 2026 results (SEC filing, August 2026)