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By HealthVetted Editorial
Reviewed & updated
Losing weight on a GLP-1 medication is not an overnight event. These drugs work gradually, the dose climbs in steps over months, and the headline numbers you see in the news come from large clinical trials that ran for well over a year. Understanding that arc — slow start, gradual climb, long plateau — sets realistic expectations and helps you stick with treatment long enough to see what it can do.
This is general information, not medical advice. Whether a GLP-1 is right for you, how it should be dosed, and how long to stay on it are decisions for you and a licensed clinician.
GLP-1 (and dual GIP/GLP-1) medications are not started at full strength. The FDA prescribing information for both Wegovy (semaglutide) and Zepbound (tirzepatide) calls for a stepwise titration: you begin at a low starting dose and increase at set intervals over a period of months until you reach a maintenance dose 34. This slow ramp exists primarily to reduce gastrointestinal side effects — nausea, diarrhea, vomiting, and constipation are the most common reactions, and easing into the dose gives the body time to adjust 34.
A practical consequence: during the first weeks and months you may be on doses below the level that produced the big results in trials. Appetite changes can begin early for some people, but the medication is still climbing toward its target dose. Patience during titration is part of the process, not a sign that the drug isn't working.
For the bigger picture of how these medications drive weight loss, see our pillar guide on [GLP-1 weight loss](/glp-1-weight-loss).
The most reliable expectations come from the large randomized trials, and it's important to read them as averages over long study periods — not as week-by-week promises.
Semaglutide (STEP 1). In the STEP 1 trial, adults with overweight or obesity who received once-weekly semaglutide lost on average about 15% of body weight over 68 weeks, alongside lifestyle intervention 1. That's roughly a year and four months of treatment to reach the reported average.
Tirzepatide (SURMOUNT-1). In the SURMOUNT-1 trial, once-weekly tirzepatide produced an average weight reduction of about 21% over 72 weeks, again with lifestyle support 2. Higher doses in the trial were associated with the larger average reductions.
Two things matter here. First, these are *averages* — individual results varied widely in both trials, with some participants losing considerably more and others considerably less 12. Second, the numbers reflect roughly 14 to 17 months of treatment, not a few weeks. Anyone expecting trial-level results in the first month is reading the headline without the timeline attached.
| Medication | Trial | Approx. average weight loss | Trial duration |
|---|---|---|---|
| Semaglutide | STEP 1 | ~15% | 68 weeks 1 |
| Tirzepatide | SURMOUNT-1 | ~21% | 72 weeks 2 |
We won't invent week-by-week pound figures, because the trials report results as group averages over their full duration — not as a fixed schedule that applies to any one person.
While we won't assign specific numbers to specific weeks, the general shape of a GLP-1 course is consistent with how the medications are dosed and studied.
The titration phase (early months). You start low and step up. Side effects, if they occur, tend to be most noticeable around dose increases 34. Weight change in this window is typically modest because you haven't yet reached the maintenance dose.
The active loss phase. Once at a maintenance dose, weight tends to decline more steadily. In the trials, weight continued to fall over many months before flattening 12. This is the longest and most productive stretch.
The plateau. Weight loss is not infinite. In both STEP 1 and SURMOUNT-1, the average curves leveled off as the trials progressed toward their endpoints 12. A plateau is expected, not a failure.
Because obesity is framed as a chronic condition, these medications are generally used as long-term treatment rather than a short course — a point worth discussing with your clinician when you think about how long results need to be maintained.
The trial averages mask real variation 12. Several factors shape where any individual lands:
If you're comparing your options, our roundups cover [the best prescription GLP-1 options](/best-prescription-glp1) and a head-to-head on [Wegovy vs Zepbound](/compare/wegovy-vs-zepbound). Individual product overviews are available for [Wegovy](/reviews/wegovy) and [Zepbound](/reviews/zepbound).
It's easy to get confused by brand names. Semaglutide is sold as Wegovy for chronic weight management and as Ozempic for type 2 diabetes 35. Tirzepatide is sold as Zepbound for weight management and as Mounjaro for type 2 diabetes 46. The weight-loss trial results above (STEP 1 and SURMOUNT-1) concern the active ingredients semaglutide and tirzepatide 12.
Expectations about results should always sit alongside safety. The prescribing information for both Wegovy and Zepbound carries a boxed warning regarding the risk of thyroid C-cell tumors observed in rodent studies, and both are contraindicated in people with a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2) 34. The most common side effects are gastrointestinal 34. For a fuller rundown, see our guide to [GLP-1 side effects](/glp-1-side-effects).
None of this replaces a conversation with a qualified prescriber, who can assess your eligibility, weigh contraindications, and set a dosing plan appropriate to you.
Think in months, not days. The dose climbs over a titration period, meaningful loss accrues over the maintenance phase, and the curve eventually flattens. The widely cited figures — roughly 15% over 68 weeks for semaglutide and roughly 21% over 72 weeks for tirzepatide — are long-run trial averages with wide individual variation 12. Set your expectations to that horizon, pair the medication with the lifestyle support used in the trials, and keep your clinician in the loop throughout.
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The medications are titrated upward over a period of months before reaching a maintenance dose, and the pivotal trials measured results over 68 weeks for semaglutide and 72 weeks for tirzepatide. Plan for a months-long horizon rather than a few weeks, and discuss what to expect with your clinician.
In clinical trials, semaglutide produced an average loss of about 15% of body weight over 68 weeks (STEP 1) and tirzepatide about 21% over 72 weeks (SURMOUNT-1). These are group averages with wide individual variation, so your result may be higher or lower.
The FDA prescribing information for Wegovy and Zepbound specifies a stepwise titration largely to reduce gastrointestinal side effects such as nausea, which tend to be most noticeable around dose increases. The gradual ramp gives the body time to adjust.
Yes. In both major trials the average weight-loss curves leveled off as the studies progressed toward their endpoints. A plateau is an expected part of the timeline, not a sign of failure.
Both contain the active ingredient semaglutide, but they are different products: Wegovy is approved for chronic weight management, while Ozempic is approved for type 2 diabetes. Similarly, Zepbound and Mounjaro both contain tirzepatide for weight management and diabetes respectively.