The honest numbers from STEP-1, SURMOUNT-1, and the regain data—including what the averages don't tell you.
The short answer: Wegovy averages 14.9% of body weight. Zepbound averages 20.9%. But "average" is doing a lot of work in those sentences, and the distribution matters as much as the mean. Here's the full picture, without the marketing spin in either direction.
The STEP-1 trial was published in the New England Journal of Medicine in 2021. It enrolled 1,961 adults with a BMI of 30 or higher (or 27+ with a weight-related condition), all without Type 2 diabetes. Participants received either semaglutide 2.4mg weekly (the Wegovy dose) or placebo for 68 weeks, combined with lifestyle counseling.
The headline numbers:
For comparison, the placebo group lost 2.4% average—most of it attributable to the lifestyle counseling component. The drug effect itself (above placebo) was roughly 12.5 percentage points.
The 14.9% average is real, but it represents the middle of a wide distribution. A meaningful proportion of STEP-1 participants didn't respond dramatically—and a meaningful proportion did extraordinarily well:
Translation: about 1 in 6 participants lost less than 5% of body weight—effectively non-responders. About 1 in 3 lost more than 20%. Most people fall somewhere in the 10-20% range. Expecting exactly 14.9% is like expecting to be exactly average height—it's statistically likely-ish, but you might be well above or below.
SURMOUNT-1 was published in NEJM in 2022, with 2,539 participants—similar design to STEP-1 but using tirzepatide at three dose levels (5mg, 10mg, and 15mg weekly). Results for the maximum 15mg dose:
These are extraordinary numbers. To put 20.9% in context: laparoscopic adjustable gastric banding (lap band) historically achieves about 15-25% excess weight loss at one year; SURMOUNT-1's results are in that territory from a weekly injection.
Even the 5mg dose group (lowest tested) averaged 15% weight loss, which rivals STEP-1's semaglutide result at maximum dose. The dose-response relationship is strong—9mg and 15mg produce progressively better outcomes.
One of the most important but least-discussed aspects of GLP-1 weight loss: these drugs take 16-18 months to reach their full effect at maximum dose. Many people expect rapid results and get discouraged at month 3 or 4, when they're often still titrating up to their target dose.
The typical dose escalation schedule for semaglutide (Wegovy):
You're not at a meaningful therapeutic dose until month 4-5. The bulk of weight loss in STEP-1 occurred between weeks 16 and 68. If you're not seeing dramatic results at 8 weeks, that's normal—you're not at the right dose yet.
Weight loss typically slows and plateaus around months 16-18. This is biological, not a sign the drug stopped working. The drug is still suppressing appetite and maintaining your new weight; you just can't continue losing indefinitely.
This is the part of the conversation that often doesn't happen upfront—and it should. When STEP-1 participants stopped taking semaglutide after 68 weeks, researchers followed them for another 52 weeks. The results from this extension study (published 2022) were sobering:
This data tells us something fundamental: GLP-1 medications address a symptom (dysregulated appetite signaling) rather than curing the underlying condition. Obesity is a chronic disease involving hormonal, neurological, and metabolic factors. When you remove the drug that's modulating those factors, they return to their previous state.
The analogy is blood pressure medication. If you take lisinopril for 5 years and your blood pressure normalizes, that doesn't mean you've fixed your blood pressure—it means the medication is working. Stop the medication, and blood pressure returns. The expectation of "I'll take this drug for a year to lose weight and then stop" is almost certainly going to result in weight regain.
This isn't defeatist—it's important clinical context. If you're going on a GLP-1, plan for it to be indefinite unless your situation changes. That affects both your financial planning and your expectations.
Who tends to do better? The trial data and post-hoc analyses suggest a few patterns:
The strongest predictor. Participants who tolerated and stayed at the maximum dose lost significantly more than those who stayed at lower doses due to side effects. If nausea is keeping you at 1mg when you're supposed to be at 2.4mg, that's meaningful—discuss slower titration with your prescriber rather than accepting the side effects or stopping.
Counterintuitively, people without Type 2 diabetes tend to lose more weight on GLP-1s than those with T2D. In STEP-1 (no T2D), semaglutide averaged 14.9%. In STEP-2 (T2D cohort), it averaged 9.6%. The leading hypothesis is that T2D patients have additional hormonal and metabolic factors that blunt the drug's effects.
This one doesn't show up in the primary trial analysis because it wasn't measured, but it matters clinically. GLP-1s suppress appetite globally—which means total calorie intake drops, and with it, protein intake if you're not deliberate. Inadequate protein during significant weight loss leads to muscle mass loss, which slows metabolism and makes weight regain more likely.
The recommendation that's becoming standard in obesity medicine: 1.2–1.6 grams of protein per kilogram of body weight per day, plus resistance training at least 2x weekly. This isn't mandatory for weight loss, but it's the difference between losing 20 pounds of mostly fat vs. 20 pounds of fat and muscle.
Percentage weight loss is fairly consistent regardless of starting weight, but absolute pounds lost scale with starting weight. Someone starting at 300 pounds losing 15% loses 45 pounds. Someone starting at 200 pounds losing 15% loses 30 pounds. The drug effect is proportional.
| Starting Weight | Low Responder (10%) | Average (15%) | High Responder (20%) |
|---|---|---|---|
| 200 lbs | −20 lbs | −30 lbs | −40 lbs |
| 250 lbs | −25 lbs | −37.5 lbs | −50 lbs |
| 300 lbs | −30 lbs | −45 lbs | −60 lbs |
| 350 lbs | −35 lbs | −52.5 lbs | −70 lbs |
Based on approximate percentages from STEP-1/SURMOUNT-1 distributions. Individual results vary. Use tirzepatide (Zepbound/Mounjaro) percentages for that drug, which run higher.
Go in with calibrated expectations. These drugs work—better than anything previously available—but they're not magic. About 1 in 6 people are poor responders. Most people will land somewhere in the 10-20% range. A subset will achieve results approaching bariatric surgery outcomes.
The plateau isn't failure; it's where the drug has done its job. Plan for long-term use and the costs that entails. Protect your muscle mass intentionally. And if you're a poor responder at maximum semaglutide dose, tirzepatide is worth trying—the SURMOUNT-5 head-to-head suggests a meaningful difference even in the same population.
Most people see initial weight loss within the first 4-8 weeks, but you're not at a therapeutic dose until month 4-5 for semaglutide (following the full titration schedule). The bulk of weight loss occurs between months 4 and 16. Don't judge efficacy at 8 weeks—you're still dose-escalating.
About 17% of STEP-1 participants lost less than 5% of body weight. If you've been at the maximum tolerated dose for at least 16 weeks and haven't exceeded 5% loss, you may be a poor responder to semaglutide. This is worth discussing with your prescriber—switching to tirzepatide is reasonable in this situation, and some patients who don't respond well to one drug respond much better to the other.
Some muscle loss during significant weight loss is nearly inevitable. Studies suggest roughly 25-40% of weight lost on GLP-1s is lean mass (including muscle), which is similar to other calorie restriction approaches. You can reduce muscle loss by eating adequate protein (1.2-1.6g per kg body weight daily) and doing regular resistance training. This is clinically important—preserving muscle mass protects your metabolic rate and makes long-term weight maintenance easier.
You can, but the STEP-1 extension data shows that about two-thirds of lost weight returns within one year of stopping. Whether to continue long-term depends on your individual situation, health goals, and financial considerations. Some people successfully maintain weight loss after stopping through intensive lifestyle modification—but this requires significant effort and realistic expectations about the likely outcome.
Based on your current weight, target drug, and dose, see a personalized estimate of your expected weight loss range—including low, average, and high responder scenarios.
Weight Loss Calculator →Medical Disclaimer: The clinical trial data cited (STEP-1, SURMOUNT-1, STEP-1 extension) is accurately summarized from published literature. Individual results vary substantially. This content is educational and does not constitute medical advice. Consult a licensed healthcare provider to understand expected outcomes for your specific situation, including relevant comorbidities, medications, and health history.
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