The short answer
In clinical trials, people with obesity lost roughly 15 to 25 percent of their body weight in about a year. How much depends on the medication and the dose you reach. The effect often shows up fast. Many people notice their appetite drop early on and feel satisfied on much smaller portions.
Weight loss tends to follow a pattern, with the steepest loss over the first several months, then a steadier pace that often continues well into the first year.
By medication (trial averages)
These are trial averages, measured over about a year to a year and a half. Diet and exercise alone is the comparison group, and each bar is a drug's average from its own trial, so this is a rough comparison across studies, not one head-to-head test. Retatrutide is still in clinical trials, not yet FDA-approved, and not available by prescription.
Which loses more, semaglutide or tirzepatide?
Tirzepatide and semaglutide are the two main GLP-1 medicines. The difference is simple. Tirzepatide works on two appetite hormones, semaglutide on one. That is part of why tirzepatide tends to bring more weight loss in trials. When the two were compared head-to-head in the SURMOUNT-5 trial, tirzepatide came out ahead. More weight loss can also mean more side effects for some people. There is no single best choice. The right one is what you and your prescriber decide together.
What changes your number
- The dose you and your prescriber reach, and how long you stay on it.
- Food and movement habits alongside the medication.
- Your own body. These are averages, not promises.
Do I still have to diet and exercise?
Not the way you might fear. In the trials the medicine did the hard part by quieting appetite, so eating less stopped feeling like a battle. The studies still included everyday eating and activity alongside the medication, so reasonable habits are part of the picture. No boot camp and no crash diet.
Will I lose muscle or have loose skin?
When weight comes off quickly, some of it can be muscle, not just fat. That is true of any fast weight loss, not only GLP-1s. Research points to two things that help protect muscle: getting enough protein and a little strength activity. Loose skin is harder to predict. It depends on how much you lose, how fast, your age, and your genetics.
Keeping it off: what happens if you stop
Stopping does not erase your progress, but the appetite help goes with it. Here is what the trials and real life actually show.
- Semaglutide (STEP 1): a year after stopping, people regained about two-thirds of their loss and stayed roughly 5 to 6 percent below their starting weight.
- Tirzepatide (SURMOUNT-4): after stopping, about half came back, leaving people near 10 percent below baseline. Those who stayed on kept nearly all of it.
- Real world: results look better and vary more. In a Cleveland Clinic study of nearly 8,000 patients, about 45 percent kept the weight off a full year after stopping.
What separates the two groups is mostly the plan. Staying on a maintenance routine your prescriber sets, with enough protein and steady movement, is what the data ties to keeping the weight from creeping back.
Sources: FDA prescribing labels and the pivotal obesity trials. The approved medicines draw on trials in the New England Journal of Medicine (SURMOUNT for tirzepatide, including the SURMOUNT-5 head-to-head with semaglutide, STEP for semaglutide, ATTAIN for orforglipron). Retatrutide's figures are Lilly's Phase 3 TRIUMPH topline results (2026), as it is still investigational. Stopping figures come from follow-up trials and a 2026 Cleveland Clinic real-world study, with references such as Mayo Clinic. Figures are average weight loss at the highest dose, about a year and a half into treatment for people who stayed on it, so real-world results are usually lower. They vary by person, dose, and medication.
This is general information, not medical advice. A licensed prescriber can tell you what is realistic for you.