How much weight do you actually lose on a GLP-1? The trial numbers

Semaglutide (Wegovy): about 15% on average

The headline claims around GLP-1s range from restrained to absurd. The useful thing is that these drugs were approved on the back of large randomized trials published in top medical journals, so we do not have to guess.

The pivotal trial was STEP 1, published in the New England Journal of Medicine in 2021. Adults with obesity took semaglutide 2.4 mg weekly for 68 weeks alongside lifestyle counseling. Mean body-weight change was roughly 15%, versus about 2.4% for placebo [1]. A person starting at 100 kg lost around 15 kg on average. Averages hide a spread (many participants lost more, some less), but 68 weeks and about 15% is the honest center of gravity.

Tirzepatide (Zepbound): more, and dose-dependent

The pivotal trial was SURMOUNT-1 (NEJM, 2022), running 72 weeks. Tirzepatide is a dual-receptor drug, and its results were higher and clearly dose-dependent: roughly 15% at the low dose up to around 20 to 21% at the highest dose on average, with some analyses reporting figures up to about 22.5% depending on how missing data is handled [2]. This is why tirzepatide is often described as the more potent of the two.

Beyond the scale: the cardiovascular signal

Weight is not the only endpoint that matters. In the SELECT trial (NEJM, 2023), semaglutide reduced major adverse cardiovascular events by about 20% in people who were overweight or obese and had established cardiovascular disease but not diabetes [3]. That result reframed these drugs as more than cosmetic, a meaningful point if you or your clinician are weighing risk, not just pounds.

Three things the numbers do not say

First, they are averages under trial conditions. Participants got structured lifestyle support and close monitoring, so real-world results vary more. Second, the weight comes off slowly: these are 68 to 72-week results, the curve is gradual and tends to plateau, and there is no version of this that is fast. Third, stopping tends to reverse it, since a large fraction of lost weight returns after people stop.

A realistic frame for starting: meaningful, clinically significant weight loss over roughly a year to eighteen months (on the order of 15% for semaglutide and somewhat more for tirzepatide at higher doses), contingent on staying on the medication and pairing it with lifestyle change. Anyone promising faster or larger results is ahead of the evidence. WeighedHealth compiled the trial results, current pricing, and US prevalence data into a single free reference, every figure linked to its primary source, alongside a breakdown of what the programs actually cost.