GLP-1 medications like semaglutide and tirzepatide have reshaped the conversation around weight management, and a wider family of peptides is often mentioned alongside them. This guide explains what these compounds are, what the research actually shows, and where the honest limits of that evidence sit. The Peptide Foundation sells nothing and prescribes nothing. We rate providers and summarize the science so you can make an informed decision with a licensed clinician.
Why weight regulation is hard
Body weight is governed partly by hormones and signaling peptides, not by willpower alone. Research suggests that when people reduce calories, the body tends to defend its prior weight by increasing hunger signals and lowering resting energy expenditure. This is one reason long-term diet studies so often show initial loss followed by regain. GLP-1 based medications became prominent because they act on some of those same appetite and metabolic signals rather than on stimulant pathways.
What GLP-1 and related compounds are
GLP-1 (glucagon-like peptide-1) is a hormone the gut releases after eating. It is understood to prompt insulin release, slow gastric emptying, and act on appetite centers in the brain. Semaglutide (the active ingredient in Ozempic and Wegovy) and tirzepatide (the active ingredient in Mounjaro and Zepbound) are receptor agonists designed around this pathway. Tirzepatide is a dual agonist that also targets the GIP receptor.
Two newer or adjacent compounds come up often in the same discussions. Retatrutide is an investigational triple agonist (GIP, GLP-1, and glucagon receptors) still in clinical trials and not FDA-approved. AOD-9604 is a fragment of human growth hormone that has been studied for fat metabolism. Others sometimes marketed for metabolic goals include tesamorelin, MOTS-c, and 5-Amino-1MQ. The evidence base behind these varies widely, and most is far thinner than the GLP-1 data.
What the research actually shows
The strongest human evidence sits with the FDA-approved GLP-1 medications. In the 68-week STEP 1 trial, adults taking semaglutide alongside lifestyle counseling lost a mean of about 14.9% of body weight, compared with 2.4% on placebo. In the 72-week SURMOUNT-1 trial, tirzepatide was reported to produce mean reductions of roughly 15% to 20.9% depending on dose. Follow-up trials suggest results tend to be sustained while treatment continues and that some weight tends to return after stopping. These are averages from controlled studies, not guarantees of any individual outcome, and these medications have not been shown to work for everyone.
Retatrutide has shown large dose-dependent weight reductions in phase 2 trials, but it remains investigational and its long-term safety in humans has not been established. AOD-9604's weight and fat findings come largely from animal models, and a human weight-loss benefit has not been proven. Tesamorelin is FDA-approved specifically to reduce visceral abdominal fat in people with HIV-associated lipodystrophy, which is a narrow indication and not general weight loss. MOTS-c and 5-Amino-1MQ have early metabolic findings almost entirely in mice. Early research is a starting point, not proof that something works in people.
Muscle, fat, and body composition
Any meaningful calorie deficit, from any cause, can cost some lean mass alongside fat. Trial data on semaglutide and tirzepatide have been reported to show that the majority of weight lost is fat, though some lean mass loss also occurs. This is the honest context behind marketing claims that adjunct peptides preserve muscle, claims that are not established in humans. Adequate protein and resistance exercise are commonly discussed in the research literature as ways to protect lean mass during weight loss, and any such approach should be directed by a licensed clinician.
Brand-name drugs versus compounded versions
Ozempic, Wegovy, Mounjaro, and Zepbound are brand-name products built on semaglutide or tirzepatide. During shortages, licensed 503A and 503B compounding pharmacies have prepared compounded versions of these active ingredients when dispensed under a valid prescription. That is a different world from research-use-only products sold online outside the pharmacy system.
Safety, legality, and the gray market
GLP-1 receptor agonists carry known cautions, including gastrointestinal side effects and a boxed warning tied to a personal or family history of medullary thyroid carcinoma or MEN2 syndrome. They are not appropriate for everyone, and clinical screening matters. Separately, several peptides discussed in weight and metabolic circles are sold through a booming gray market of injectable products marketed as research chemicals. That market operates outside pharmacy regulation, and reporting has documented real health concerns about product quality and safety. A licensed clinician and a licensed pharmacy are the safeguards that gray-market sellers cannot offer.
How to find safe, legal treatment
If you want to explore GLP-1 or peptide options, start with a clinician who is licensed, reviews your history and labs, and prescribes through a licensed pharmacy. To compare vetted options, see the provider directory, and read how we rate so you understand what our scores weigh and what they deliberately exclude. Our FAQ covers common questions about legality, compounding, and what to ask a provider.
The bottom line
The GLP-1 medications have unusually strong human evidence for weight reduction, while most of the adjacent peptides remain investigational or supported mainly by animal data. Honest expectations, licensed oversight, and a real prescription are what separate a reasonable medical path from the gray market. Use the research to ask better questions, and let a qualified clinician decide what, if anything, is right for you.