Why Researchers Are So Interested in GLP-1 Medications
GLP-1 medications have been everywhere in the news lately, and the headlines can be loud. The real science behind them is more interesting and more nuanced than “a shot that melts weight.” Let’s walk through what these medications are, what the landmark trials actually showed, and the questions scientists are still asking.
Start with the hormone
GLP-1, short for glucagon-like peptide-1, is a hormone your gut releases after you eat. It helps your body handle a meal: it supports the release of insulin when blood sugar rises and it sends signals that contribute to feeling full. GLP-1 medications are designed to act on the same pathway, only more strongly and for longer than your natural hormone does. That is why they were first developed for type 2 diabetes and are now also used for chronic weight management. Newer tirzepatide-based medicines act on a second hormone pathway (GIP) as well as GLP-1.
The two trials everyone talks about
Much of the excitement comes from two large, randomized, placebo-controlled trials published in the New England Journal of Medicine. Both enrolled adults with obesity, or with overweight plus a weight-related condition, who did not have diabetes. Here is how they compare.
| STEP 1 (semaglutide) | SURMOUNT-1 (tirzepatide) | |
|---|---|---|
| Published | 2021 | 2022 |
| Participants | About 1,960 adults | 2,539 adults |
| Length | 68 weeks | 72 weeks |
| Average weight loss | 14.9% (placebo: 2.4%) | About 16% to 22.5% depending on dose, among those who stayed on treatment |
| Big losers | 50.5% lost 15% or more (placebo: 4.9%) | At the two higher doses, 50% and 57% lost 20% or more (placebo: 3%) |
One thing to keep in mind: participants in both studies also got lifestyle support, so the results show the medication plus counseling, not the medication alone.
Why researchers find the results so striking
The size of the effect is the headline. Lifestyle programs and older weight-loss drugs have rarely produced average losses this large across thousands of people. And the results were not only about the scale: in STEP 1, measures such as waist circumference, blood pressure and physical function improved along with body weight. That is encouraging news for the people who took part.
The deeper reason for the buzz is biology. The hormone pathways these medications target are found in the brain, gut, pancreas and other organs, so scientists are studying whether the medications affect more than appetite and blood sugar. That work is ongoing, and we will share what we learn as the evidence grows.
The side effects and trade-offs
These are real medications with real downsides, and the trials say so plainly. It helps to go in with clear eyes.
- Digestive symptoms are the most common problem. In both trials the most frequent side effects were gastrointestinal and tended to cluster during dose increases.
- Serious events were reported more often with the drug. In STEP 1, 9.8% of people on semaglutide had a serious adverse event, versus 6.4% on placebo.
- Some people stopped treatment. In SURMOUNT-1, between 4.3% and 7.1% of people on tirzepatide stopped because of side effects, compared with 2.6% on placebo.
Caveats worth knowing
Trial participants are not everyone. In STEP 1, about three-quarters were women and three-quarters were white, so results may look different in other groups. Trials also end. What happens after someone stops the medication, how long the benefits last, and how much of the weight lost is muscle rather than fat are all active research questions, which is one reason dietitians emphasize protein and strength training for people using these medications. We cover the food side in building a balanced plate when your appetite is small and how much protein you actually need. And the medications are already changing what people buy: see how GLP-1 medications are changing the way people shop for food.
Where this leaves you
The evidence is strong that GLP-1 and related medications can produce large average weight loss in the people studied, and that they come with trade-offs that call for medical supervision. Whether one is right for you is a conversation for you and your prescriber. The science is moving quickly, and we will keep this article up to date as it does.
Sources
- Wilding JPH, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med. 2021;384:989-1002. doi:10.1056/NEJMoa2032183
- Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). N Engl J Med. 2022;387:205-216. doi:10.1056/NEJMoa2206038
- American College of Cardiology trial summaries: STEP 1 and SURMOUNT-1.
- Chang RS, Hu J-R, Yeh H-C. Once-weekly semaglutide with lifestyle intervention results in clinically significant weight loss. J Gen Intern Med. 2022. PMC9130404
This article describes research and is not medical advice; see our Medical Disclaimer. It does not recommend any specific medication or provider.
Published October 2, 2026. We update articles when new evidence or official guidance changes. If you spot an error, tell us.
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