Do GLP-1s Work? What the Trial Data Shows

Last updated October 20, 2026

Short answer: Yes, on average. In the trials behind the FDA labels, adults taking Wegovy lost 14.9% of their body weight at 68 weeks (2.4% on placebo), and adults taking the highest Zepbound dose lost 20.9% at 72 weeks (3.1% on placebo). Averages hide a range, though: roughly 1 in 6 people on Wegovy and about 1 in 11 on the top Zepbound dose lost less than 5%.

What the main trials found

Both medications were tested against placebo in adults with obesity, or overweight plus a weight-related condition, and without type 2 diabetes. Everyone in the trials, including the placebo group, received lifestyle counseling on a reduced-calorie diet and more physical activity. The numbers below are from the clinical studies section of each prescribing label.

Wegovy (semaglutide 2.4 mg), 68 weeks, 1,961 adults

Zepbound (tirzepatide), 72 weeks, 2,539 adults

To make that concrete: 14.9% of 200 pounds is about 30 pounds, and 20.9% of 200 pounds is about 42 pounds. Those are group averages, not predictions for any one person.

The average is not the whole story

The rows that say "lost at least" show how wide the range was. On Wegovy, about 83.5% of people lost 5% or more, which means roughly 1 in 6 did not reach that mark. On the highest Zepbound dose, 90.9% reached 5%, so about 1 in 11 did not. At the other end, 30.2% on Wegovy and 56.7% on Zepbound 15 mg lost at least 20%.

Dose matters as well. The Zepbound results rise with each dose, and the Wegovy figures are for the 2.4 mg maintenance dose. Many people stay on a lower dose, so their own results can differ.

Why your results may differ from the trial

• Trial participants received structured diet and activity counseling throughout. Outside a trial, support varies widely.
• The headline averages are for the full maintenance dose, which people reach only after a dose-escalation period of several months.
• Some people stop early. In the Zepbound trial, 14% to 16% of people on each dose stopped the study drug before the end.
• People with type 2 diabetes lost less on average in the same programs. Wegovy averaged -9.6% (placebo -3.4%) at 68 weeks in adults with type 2 diabetes, and Zepbound 15 mg averaged -14.7% (placebo -3.2%) at 72 weeks.
• Ozempic is a lower-dose semaglutide product approved for type 2 diabetes. The figures above are for Wegovy, not Ozempic.

Semaglutide vs. tirzepatide head to head

In SURMOUNT-5, which compared the two directly over 72 weeks, tirzepatide produced an average loss of 20.2% versus 13.7% for semaglutide. See our full comparison for the details.

What happens next

Weight loss on these medications slows as it approaches a plateau, so timing matters as much as the total. Our timeline guide explains the curve, and what happens after treatment ends is covered in what happens when you stop a GLP-1.