Many peptides are sold for research only and aren’t approved for people. We know some people take them anyway. Learn what the research really shows, then join our community, where people share what they noticed, including side effects, so nobody has to figure it out alone.
Plain-language explanations. Linked sources. Room for uncertainty.
Meet your molecular messengers
Made by the pancreas, insulin helps move glucose from the blood into cells. This familiar hormone is built from two peptide chains.
A desert lizard. A Nobel Prize. Two tiny changes. Follow the stories that make these molecules so fascinating.
Researchers found exendin-4 in the Gila monster. A synthetic version became exenatide, a medicine for type 2 diabetes. An unlikely animal helped open a new chapter in hormone research.
1958
Nobel Prize in Chemistry
Frederick Sanger worked out the order of insulin’s 51 amino acids. It was the first protein sequence to be determined, a breakthrough recognised with the 1958 Nobel Prize.
Source: MRC Laboratory of Molecular BiologyOxytocin and vasopressin each contain nine amino acids and differ at just two positions. Yet one is central to childbirth and milk release, while the other helps regulate the body’s water balance.
Source: Endotext / NCBI BookshelfTry reading a research headline like a scientist. The important question is often who—or what—was actually studied.
Imagine this headline
A peptide shows a promising effect in a cell study.
Choose an answer to see the explanation.
Results
Average weight lost in the main published trials of today’s leading medicines, each compared with a placebo.
Each medicine compared with its trial’s placebo group. Ordered by reported average; this is not a head-to-head ranking.
Retatrutide · Experimental
12 mg weekly
Phase 2 · 48 weeks · 338 people
Tirzepatide · Approved
15 mg weekly (Zepbound)
SURMOUNT-1 · 72 weeks · 2,539 people
CagriSema · Experimental
Cagrilintide 2.4 mg + semaglutide 2.4 mg weekly
REDEFINE 1 (phase 3) · 68 weeks · 3,417 people
Semaglutide · Approved
2.4 mg weekly injection (Wegovy)
STEP 1 · 68 weeks · 1,961 people
Semaglutide · Approved (US)
25 mg daily pill (Wegovy pill)
OASIS 4 · 64 weeks · 307 people
Cagrilintide · Experimental
2.4 mg weekly, studied alone
REDEFINE 1 (phase 3) · 68 weeks · 3,417 people
Average body weight lost
Each human trial had different people, doses and lengths, so compare with care. The bars describe approved or experimental medicines studied under medical supervision with diet and exercise advice, not laboratory research products. They use full journal reports; conference findings and different endpoints appear separately below.
| Medicine | Trial | People | Weeks | Medicine | Placebo | Source |
|---|---|---|---|---|---|---|
| Retatrutide, 12 mg weekly | Phase 2 | 338 | 48 | 24.2% | 2.1% | PubMed |
| Tirzepatide, 15 mg weekly (Zepbound) | SURMOUNT-1 | 2,539 | 72 | 20.9% | 3.1% | PubMed |
| CagriSema, Cagrilintide 2.4 mg + semaglutide 2.4 mg weekly | REDEFINE 1 (phase 3) | 3,417 | 68 | 20.4% | 3.0% | PubMed |
| Semaglutide, 2.4 mg weekly injection (Wegovy) | STEP 1 | 1,961 | 68 | 14.9% | 2.4% | PubMed |
| Semaglutide, 25 mg daily pill (Wegovy pill) | OASIS 4 | 307 | 64 | 13.6% | 2.2% | PubMed |
| Cagrilintide, 2.4 mg weekly, studied alone | REDEFINE 1 (phase 3) | 3,417 | 68 | 11.5% | 3.0% | PubMed |
CagriSema combines cagrilintide with semaglutide. Its row and the cagrilintide-alone row share the REDEFINE 1 trial and placebo group. Both use estimates that include participants regardless of whether they stayed on treatment. The 3,417 people shown is the total trial population: 2,108 received the combination, 302 cagrilintide alone, 302 semaglutide alone, and 705 placebo.
These findings do not provide comparable average human body-weight-loss results. Animal body weight and human fat volume measure different things, so they are shown separately from the bars.
Animal research · conference abstract
A difference versus vehicle in rats is not average weight lost by people. It cannot establish superiority to retatrutide in humans.
Human fat-volume subgroup · conference report
12.01% less visceral fat is not 12.01% less body weight. CBL-514 is an experimental small molecule, not a peptide.
Animal research · peer-reviewed study
The animal study also found kidney tubular injury. The registered phase 1 study in men with prostate cancer and obesity enrolled four people and was terminated. It does not establish safety or weight-loss effectiveness in people.
News & articles
Recent studies and decisions, written so anyone can follow them, with every source linked.
GuideReading the evidence
A promising mechanism, an animal experiment and a human trial answer different questions. Here is how to tell which kind of evidence you are reading.
GuideReading the evidence
A percentage means little without its denominator. Learn why changes in body weight, a fat deposit and a measurement in rats belong in different comparisons.
StudyWeight management
The experimental peptide combines GLP-1, GIP, amylin and calcitonin activity. Here is what the original research can tell us about weight loss.
Videos
Hand-picked videos, mostly from doctors, including some skeptical ones.
Nick Norwitz
How GLP-1 medicines work in the gut and brain, in clear language.
Nick Norwitz, MD, PhD
Watch on YouTubePeter Attia MD
Two doctors weigh the benefits against the downsides, including muscle loss and cost.
Peter Attia, MD, with diabetes researcher Ralph DeFronzo, MD
Watch on YouTubeDoctor Mike
A practicing doctor looks at the peptide trend and separates the evidence from the hype.
Mikhail Varshavski, DO, family medicine physician
Watch on YouTube