Tirzepatide clinical trial results explained (and what they cost per pound)
The SURMOUNT trials in plain language — dose-by-dose weight loss, the semaglutide head-to-head, and a framework for turning efficacy into cost-per-result.
What the SURMOUNT trials actually measured
Tirzepatide's weight-loss evidence base is the SURMOUNT program — a series of phase 3 randomized trials of the FDA-approved brand product (Zepbound/Mounjaro). The pivotal trial, SURMOUNT-1, enrolled 2,539 adults with obesity or overweight without type 2 diabetes and ran 72 weeks. Mean weight reduction was dose-dependent: roughly 15.0% at 5 mg, 19.5% at 10 mg, and 20.9% at 15 mg, versus about 3.1% on placebo. A striking share of participants crossed high thresholds — more than half of the 15 mg group lost at least 20% of body weight.
Later trials extended the picture: SURMOUNT-2 in patients with type 2 diabetes (smaller average loss, as is typical for GLP-1 therapies in diabetes), SURMOUNT-3 studying tirzepatide after an intensive lifestyle lead-in, and SURMOUNT-4 examining what happens when treatment stops — a result we cover in depth in our stopping-and-maintenance analysis.
The head-to-head result that changed the conversation
For years, comparisons between tirzepatide and semaglutide relied on cross-trial inference. SURMOUNT-5 ended that: a 751-patient, 72-week open-label trial pitting maximum-tolerated tirzepatide against maximum-tolerated semaglutide in adults with obesity without diabetes. Tirzepatide produced 20.2% mean weight loss versus 13.7% for semaglutide, and 31.6% of tirzepatide patients reached at least 25% loss versus 16.1% on semaglutide. Gastrointestinal side effects leading to discontinuation were actually lower on tirzepatide (2.7%) than semaglutide (5.6%).
Turning efficacy into cost-per-result
Efficacy only becomes a buying decision when you divide by price. Using July 2026 flat-rate compounded pricing (~$186/month, ~$2,232/year) against SURMOUNT-1's dose-response, 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. The table frames the math; it does not promise you'll match trial averages.
| Scenario (annual) | Cost/year | Trial-avg % lost (dose) | Cost per 1% (illustrative) |
|---|---|---|---|
| Flat-rate compounded ($186/mo) | $2,232 | ~20.9% (15 mg) | ~$107 |
| Dose-tiered compounded (trajectory) | ~$5,148 | ~20.9% (15 mg) | ~$246 |
| Brand Zepbound retail ($1,175/mo) | ~$14,100 | ~20.9% (15 mg) | ~$675 |
Illustrative only. Percent-lost figures are brand-trial averages, not guarantees or claims about compounded products; cost-per-percent divides annual cost by the trial-average outcome purely to compare pricing structures.
What these numbers don't say
Three honest caveats. First, trial averages hide wide individual variation — some participants lost far more, some far less. Second, SURMOUNT studied the FDA-approved brand; compounded tirzepatide has no equivalent trial base, so applying these percentages to a compounded product is an assumption, not a finding. Third, weight loss on any GLP-1 tends to reverse substantially after stopping, which is why the durable comparison is annual cost of continued therapy, not a one-time price. For that, use our cost calculator and the maintenance-economics piece.
Frequently asked questions
How much weight did people lose on tirzepatide in trials?
In SURMOUNT-1 (72 weeks, adults with obesity without diabetes), mean weight loss was about 15% at 5 mg, 19.5% at 10 mg, and 20.9% at 15 mg, versus ~3.1% on placebo. Individual results vary and these figures are for the FDA-approved brand product.
Is tirzepatide more effective than semaglutide?
In the head-to-head SURMOUNT-5 trial, tirzepatide produced 20.2% mean weight loss versus 13.7% for semaglutide over 72 weeks — about 47% more relative weight loss — and more tirzepatide patients reached ≥25% loss (31.6% vs 16.1%). Efficacy is one factor; cost, tolerability, and clinical suitability also matter.
Do compounded tirzepatide products match the trial results?
There is no trial base for compounded tirzepatide specifically. The SURMOUNT results describe the FDA-approved brand product. Compounded products are not FDA-approved and their real-world weight-loss performance is not established by these trials; treat trial percentages as context, not a guarantee.
What is the cost per percent of weight loss?
Dividing July 2026 annual cost by SURMOUNT-1's 15 mg average (~20.9%) gives roughly $107 per percentage point on a $186/mo flat-rate plan, ~$246 on a dose-tiered trajectory, and ~$675 at brand retail — an illustrative pricing comparison, not a clinical claim about any individual's results.
References
- Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). N Engl J Med. 2022.
- Aronne LJ, et al. Tirzepatide vs semaglutide in obesity (SURMOUNT-5). N Engl J Med. 2025; NCT05822830.
- Eli Lilly. Zepbound (tirzepatide) Prescribing Information, FDA label.
- TirzepatidePriceGuide.com July 2026 price report — provider-advertised pricing, checked July 2026.
Clinical figures cited from published trial reports and FDA labeling; pricing figures from provider-advertised rates checked July 2026 and subject to change. This article is educational and is not medical or financial advice.