Semaglutide clinical trial results explained (and what they cost per pound)
The STEP trials in plain language — the pivotal 14.9% result, two-year durability, regain after stopping, and a framework for turning efficacy into cost-per-result.
STEP 1: the trial that defined semaglutide for weight loss
Semaglutide's weight-management evidence base is the STEP program — a series of phase 3 randomized trials of the FDA-approved brand product (Wegovy). The pivotal STEP 1 trial enrolled 1,961 adults with obesity or overweight-plus-comorbidity, without diabetes, and ran 68 weeks. Mean weight loss was about 14.9% with semaglutide 2.4 mg versus 2.4% on placebo. The co-primary endpoint of losing at least 5% of body weight was reached by 86.4% of the semaglutide group versus 31.5% on placebo — an odds ratio around 11.
The full STEP program
Later trials extended the picture. STEP 3 paired semaglutide with intensive behavioral therapy (~16% loss). STEP 4 studied what happens when treatment continues versus stops after a 20-week lead-in. STEP 5 followed patients for two years and found sustained mean loss of about 15.2%, showing the effect persists with continued treatment. And the STEP 1 extension revealed the flip side: after stopping, participants regained about two-thirds of lost weight within a year — the subject of our maintenance-economics piece.
| Trial | Duration | Mean weight loss | Note |
|---|---|---|---|
| STEP 1 | 68 weeks | ~14.9% | Pivotal; no diabetes |
| STEP 3 | 68 weeks | ~16.0% | + intensive behavioral therapy |
| STEP 5 | 104 weeks | ~15.2% | Two-year sustained |
| STEP 1 extension | +52 wk off-drug | ~5.6% net | Regain after stopping |
Turning efficacy into cost-per-result
Efficacy becomes a buying decision when you divide by price. Using July 2026 flat-rate compounded pricing (~$145/month, ~$1,740/year) against STEP 1's ~14.9% average, the implied cost per percentage point of expected weight loss is far lower than at brand retail — though the compounded product is not FDA-approved and its real-world performance is not established by these brand trials.
| Scenario (annual) | Cost/year | Trial-avg % lost | Cost per 1% (illustrative) |
|---|---|---|---|
| Flat-rate compounded ($145/mo) | $1,740 | ~14.9% | ~$117 |
| Membership model (~$230/mo) | ~$2,760 | ~14.9% | ~$185 |
| Brand Wegovy retail (~$1,349/mo) | ~$16,188 | ~14.9% | ~$1,086 |
What these numbers don't say
Three honest caveats. Trial averages hide wide individual variation. STEP studied the FDA-approved brand; compounded semaglutide has no equivalent trial base, so applying these percentages to a compounded product is an assumption, not a finding. And weight loss reverses substantially after stopping, so the durable comparison is annual cost of continued therapy. Use our cost calculator to model your situation.
How STEP compares across patient groups
The STEP program deliberately tested semaglutide across different populations, and the results are not identical from one trial to the next — a nuance that matters when you're translating headline figures into personal expectations. STEP 2 studied adults who also had type 2 diabetes and found smaller average weight loss (around 9.6%), reflecting a consistent pattern across GLP-1 research: people with diabetes tend to lose somewhat less weight than those without. STEP 3 added intensive behavioral therapy to the medication and reached roughly 16%, showing that structured lifestyle support meaningfully amplifies the drug effect rather than being redundant to it. STEP 8 compared semaglutide directly against an older GLP-1 agonist, liraglutide, and semaglutide produced substantially greater loss.
Two lessons fall out of this for a cost-conscious reader. First, your own comorbidities shift the expected benefit — a diabetic patient should anchor expectations closer to STEP 2 than STEP 1. Second, the program that surrounds the molecule matters: the STEP 3 uplift from behavioral support is exactly the kind of bundled service that separates a bare medication-only plan from a program with real coaching. When we weight clinical support in our provider rubric, this is the evidence behind that choice — the trial data say the wrapper around the drug changes the result, not just the experience. None of these figures are promises; they are trial averages, and individual response varies widely around every one of them.
Frequently asked questions
How much weight did people lose on semaglutide in trials?
In STEP 1 (68 weeks, adults with obesity without diabetes), mean weight loss was about 14.9% with semaglutide 2.4 mg versus 2.4% on placebo, and 86.4% lost at least 5% of body weight. Individual results vary and these figures are for the FDA-approved brand product.
Does semaglutide weight loss last?
In the two-year STEP 5 trial, sustained mean loss of about 15.2% was maintained with continued treatment. However, the STEP 1 extension showed that after stopping, participants regained about two-thirds of lost weight within a year.
Do compounded semaglutide products match trial results?
There's no trial base for compounded semaglutide specifically. STEP results describe the FDA-approved brand product. Compounded products are not FDA-approved and their real-world performance is not established by these trials.
What is the cost per percent of weight loss?
Dividing July 2026 annual cost by STEP 1's ~14.9% average gives roughly $117 per percentage point on a $145/mo flat plan, ~$185 on a membership model, and ~$1,086 at brand retail — an illustrative pricing comparison, not a clinical claim.
References
- Wilding JPH, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med. 2021.
- Garvey WT, et al. Two-year effects of semaglutide (STEP 5). Nat Med. 2022.
- Wilding JPH, et al. Weight regain after withdrawal of semaglutide (STEP 1 extension). Diabetes Obes Metab. 2022.
- Novo Nordisk. Wegovy (semaglutide) Prescribing Information, FDA label.
Clinical figures from published trials and FDA labeling; pricing from provider-advertised rates checked July 2026 and subject to change. Educational, not medical or financial advice.