GLP-1 drugs copy a gut hormone that tells your brain you are full and slows your stomach. In the main trials people lost 15% to 21% of their body weight on average, heart attacks and strokes fell, and most of the weight came back when the drug stopped. Here is every approved product, every major trial and what is coming next.
Checked against FDA labels and trial publications, October 2026
Your intestine releases GLP-1 after you eat. It is a peptide about 30 amino acids long, and an enzyme called DPP-4 chops it up within minutes. The drugs are modified copies built to resist that enzyme, so a single injection works for days.
The weight loss comes mainly from eating less. People on these drugs report feeling full sooner and thinking about food less. The blood sugar effect is glucose-dependent: insulin goes up only when sugar is high, which is why GLP-1 drugs alone rarely cause hypoglycemia.
Newer drugs add other gut and pancreatic hormone receptors on top of GLP-1.
GLP-1. Fullness signals in the brainstem and hypothalamus, slower stomach emptying, insulin release only when blood sugar is up.
GIP. A second gut hormone. Adds to the insulin effect and appears to blunt nausea; how it adds weight loss is still argued over.
Glucagon. Raises energy use and pulls fat out of the liver. On its own it raises blood sugar, which is why it is paired with GLP-1.
Amylin. Released with insulin. Adds fullness through a separate brain pathway and slows stomach emptying.
Same molecule, different brand: Ozempic and Wegovy are both semaglutide, and Mounjaro and Zepbound are both tirzepatide. The brand decides which condition the label covers and which doses come in the box.
The label dose schedules, including how each drug is stepped up, are in the GLP-1 titration viewerMembers. Doses used in each trial are in the studied-dose tables on the semaglutide and tirzepatide pages for free members.
Each bar is the average weight change in a drug's main obesity trial, in people without diabetes. Tap a bar for the trial size, length and source.
Average body weight lost
Tirzepatide Zepbound, Mounjaro
Lean mass: About 25% of the weight lost was lean mass in the 160-person DEXA substudy.
Trials differ in length, population and how they handle people who stopped the drug, so treat close bars as roughly equal. The one head-to-head trial, SURMOUNT-5, found 20.2% on tirzepatide vs 13.7% on semaglutide at 72 weeks.
These come mostly during dose increases and usually ease. They are the reason the labels step the dose up slowly.
Lean mass on a DEXA scan includes muscle, organs and water, so it is not all muscle. The two substudies measured at different times in different people, so do not read the gap as a direct comparison.
Any large weight loss takes some lean tissue with it, because a lighter body needs less muscle to carry it. What worries clinicians is the size of the loss in older adults, who have less muscle to spare.
Neither trial assigned exercise or a protein target, so neither can tell you how much resistance training changes the split. Drugs designed to protect muscle during GLP-1 weight loss are in trials, and the muscle growth hub covers what has been tested.
Blood pressure, blood sugar and cholesterol improvements faded along with the weight in the STEP 1 extension. These results are why the labels describe chronic weight management rather than a course of treatment.
Pharmacies were allowed to make copies only while the drugs were in shortage. The full rules for 503A and 503B pharmacies and research-use-only labels are in the legal status guide, and the quality differences are in pharma vs compounded vs research.
Retatrutide filings, CagriSema decisions, new label indications and FDA compounding actions, checked against the source. One email a week.