Tirzepatide shows a higher average in its pivotal trial. That gap of about 6 percentage points is real and clinically meaningful. But the two trials were run separately, on overlapping but not identical populations, with different durations. Neither number is a guarantee for any individual.
How the two drugs actually differ
Both drugs work primarily through appetite suppression and slowing how fast food leaves your stomach. The difference is in which receptors they target.
Mimics glucagon-like peptide-1, a hormone released after eating. Reduces appetite by acting on receptors in the brain and gut. The active ingredient in both Wegovy (obesity dose) and Ozempic (diabetes dose).
Does everything semaglutide does, plus activates the GIP receptor (glucose-dependent insulinotropic polypeptide). The GIP component appears to act on fat tissue in ways that GLP-1 alone does not, which likely explains the additional weight loss seen in trials.
Mounjaro and Zepbound are the same molecule (tirzepatide). Mounjaro is approved for type 2 diabetes. Zepbound is approved for obesity. Same drug, different brand name, different indication on the label.
How results distribute in each trial
The average does not tell the full story. Here is the responder breakdown for both trials at their highest doses.
| Weight loss threshold | Wegovy (14.9% avg) | Tirzepatide 15mg (20.9% avg) |
|---|---|---|
| 5% or more | 86% | 91% |
| 10% or more | 69% | 83% |
| 15% or more | 50% | 69% |
| 20% or more | 32% | 50% |
| 25% or more | not reported | 36% |
Half of people on the 15mg tirzepatide dose lost 20% or more. On Wegovy, that number was one in three. The floor is also higher: 91% of tirzepatide participants crossed the 5% threshold versus 86% on Wegovy.
Tirzepatide is also dosed in tiers. The 15mg is the highest dose, reached after a slow escalation over five months. The 10mg results are slightly lower at 19.5% average, and 5mg averaged 16.0%.
Why you cannot compare these numbers directly
These were not head-to-head trials.
STEP 1 and SURMOUNT-1 were run separately, by different research teams, for different companies. No randomized controlled trial has directly compared semaglutide 2.4mg and tirzepatide in the same population at the same time. The 6-point gap is real, but it is not the kind of controlled comparison that rules out confounding factors.
A few specific differences between the trials that affect interpretation:
SURMOUNT-1 ran 72 weeks. STEP 1 ran 68 weeks. Four extra weeks of treatment is not the full explanation for the gap, but it is a factor.
Both trials required BMI of 30 or higher, or 27 or higher with a weight-related condition. STEP 1 excluded people with type 2 diabetes. SURMOUNT-1 also excluded people with diabetes in its primary cohort. The populations are similar but not identical in terms of baseline characteristics.
As of mid-2026, no peer-reviewed randomized trial has published a direct comparison of the two drugs in the same study population. Observational data and indirect meta-analyses exist, but they carry more uncertainty than a controlled trial.
None of this changes the fact that tirzepatide shows higher averages in the available evidence. It just means you should read the gap as "tirzepatide probably leads to more weight loss for most people" rather than "tirzepatide is exactly 6 points better."
Side effects
Both drugs share a similar side effect profile, since both act on GLP-1 receptors. The most common issues are gastrointestinal.
| Side effect | Wegovy (STEP 1) | Tirzepatide (SURMOUNT-1) |
|---|---|---|
| Nausea | 44% | 33% |
| Diarrhea | 30% | 23% |
| Vomiting | 24% | 13% |
| Constipation | 24% | 17% |
| Discontinued due to side effects | 7% | 7% |
Tirzepatide shows lower rates on most GI side effects in its trial. Discontinuation rates were the same. These are trial-reported rates under controlled conditions and do not account for how side effects vary with dose escalation speed, food choices, and individual sensitivity.
Cost
At list price, both drugs run over $1,000 per month without insurance or savings programs. Tirzepatide (Mounjaro/Zepbound) lists slightly lower than Wegovy, though actual cost depends heavily on insurance, savings cards, and how you access the medication.
The cost comparison calculator on this site breaks out cash price, GoodRx estimates, and manufacturer savings card pricing for each drug side by side, updated monthly.
Compare costs and timelines
The weight loss calculator shows your projected timeline for each drug. The cost comparison breaks out what you would pay under each pricing path.