The two dominant GLP-1 medications — semaglutide (sold as Wegovy and Ozempic) and tirzepatide (sold as Zepbound and Mounjaro) — are often treated as interchangeable by the media. They're not. While both target the GLP-1 receptor, their mechanisms, efficacy profiles, and practical considerations differ in ways that matter.
Mechanism of Action
Semaglutide is a pure GLP-1 receptor agonist. It mimics the natural incretin hormone GLP-1, acting on receptors in the brain to reduce appetite and in the pancreas to improve insulin secretion.
Tirzepatide is a dual GIP/GLP-1 receptor agonist. It activates both the GLP-1 receptor and the glucose-dependent insulinotropic polypeptide (GIP) receptor. This dual mechanism appears to produce additive effects on both appetite suppression and metabolic improvement.
Efficacy: What the Trials Show
The STEP trials (semaglutide) and SURMOUNT trials (tirzepatide) provide the best comparative data, though they were not head-to-head studies:
- Semaglutide 2.4mg: Average 15.8% total body weight loss at 68 weeks (STEP 1)
- Tirzepatide 15mg: Average 22.5% total body weight loss at 72 weeks (SURMOUNT-1)
The difference is meaningful. However, direct head-to-head data from the SURPASS trials (which compared the two in diabetes patients) and emerging real-world evidence suggest tirzepatide's advantage, while real, may be somewhat smaller than comparing separate trial populations implies.
Trial populations differ. Real-world adherence differs from clinical trial adherence. The best medication is the one your body tolerates well and that you can access consistently.
Side Effect Profiles
Both medications share a similar GI side effect profile — nausea, vomiting, diarrhea, and constipation are the most common complaints. Rates are roughly comparable:
- Nausea: ~30-45% of patients on either drug (most common during titration)
- Serious GI events: 4-7% discontinuation rate in trials for both
- Injection site reactions: Slightly more common with tirzepatide
Some clinicians report anecdotally that tirzepatide may cause less nausea at equivalent efficacy levels, but this hasn't been conclusively demonstrated in controlled settings.
Cost Comparison
Without insurance, both medications carry significant list prices:
- Wegovy (semaglutide): ~$1,300-1,400/month
- Zepbound (tirzepatide): ~$1,000-1,100/month
Insurance coverage varies enormously. Telehealth platforms and compounding pharmacies have introduced lower-cost options for both, though quality and regulatory status vary. We cover this in detail in our compounding pharmacies guide.
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Supply has been a persistent issue for both medications since 2023. As of early 2026:
- Semaglutide: Supply has largely stabilized. Most pharmacies can fill prescriptions within a week.
- Tirzepatide: Higher-dose pens (10mg, 12.5mg, 15mg) still see intermittent shortages in some regions.
Which Should You Choose?
There's no universal answer, but here are some guiding principles:
- Choose semaglutide if: You prioritize the longest safety track record, wider insurance coverage, or your provider has more experience prescribing it
- Choose tirzepatide if: You want the potentially higher efficacy ceiling, have had inadequate response to semaglutide, or find it more affordable through your plan
Both are effective medications with strong clinical evidence. Discuss your specific health profile, insurance situation, and goals with your prescribing physician.