What Clinical Trials Show for Weight Loss Results
Zepbound (tirzepatide) demonstrated greater average weight loss than Wegovy (semaglutide) in head-to-head trials. In the SURMOUNT-5 trial, Zepbound users lost 20.2% of body weight on average after 72 weeks, compared to 13.7% for Wegovy users—a 47% relative advantage for Zepbound.[1] Both drugs outperformed placebo, but Zepbound consistently hit higher marks across doses (10mg or 15mg weekly injections).
How They Work and Why the Difference
Zepbound targets both GLP-1 and GIP receptors, potentially enhancing appetite suppression and fat metabolism more than Wegovy's single GLP-1 action.[2] This dual mechanism appears to drive superior results, especially in patients with obesity (BMI ≥30) or overweight with comorbidities. Real-world data from registries like TriNetX echo trial findings, with Zepbound averaging 15-21% loss versus 10-15% for Wegovy over 12 months.[3]
Who Responds Better to Each
Zepbound edges out in most subgroups, including those with type 2 diabetes (18.4% vs. 12.5% loss) and higher BMIs (>35).[1] Wegovy may suit patients sensitive to GI side effects, as Zepbound causes more nausea (25% vs. 20%) and diarrhea, though rates drop after dose escalation.[4] About 30% of Wegovy users lose ≥20% body weight, versus 40-50% on Zepbound.[1][2]
Head-to-Head vs. Separate Trials
SURMOUNT-5 is the only direct comparison; earlier data pitted each against placebo. Zepbound's phase 3 trials (SURMOUNT-1/2) showed 15-22% loss at 72 weeks, outpacing Wegovy's STEP trials (14-16% loss).[5] No long-term (>1 year) direct data exists yet.
Cost, Access, and Switching
Zepbound lists at $1,060/month without insurance, matching Wegovy's price; coupons cut it to $550 for eligible patients.[6] Shortages hit both, but Zepbound's newer approval (November 2023) limits supply. Switching from Wegovy often yields extra 5-7% loss on Zepbound, per clinician reports.[3]
Side Effects and Dropout Risks
Both cause similar GI issues (nausea, vomiting), but Zepbound has slightly higher rates and gallbladder problems (1.6% vs. 0.7%).[1][4] Dropout rates were comparable (7-8%) in SURMOUNT-5. Heart benefits favor Wegovy (proven CV risk reduction), while Zepbound's are pending.[2]
[1] Lilly press release, SURMOUNT-5 results (Dec 2024). https://investor.lilly.com/news-releases/news-release-details/lillys-zepboundr-tirzepatide-superior-wegovyr-semaglutide-head
[2] NEJM, SURMOUNT-1 (2022). https://www.nejm.org/doi/full/10.1056/NEJMoa2206038
[3] JAMA Network Open, real-world tirzepatide vs. semaglutide (2024). https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2821368
[4] FDA labels, Zepbound vs. Wegovy. https://www.accessdata.fda.gov/drugsatfda_docs/label/2023/217806s000lbl.pdf
[5] NEJM, STEP 1-5 trials (2021). https://www.nejm.org/doi/full/10.1056/NEJMoa2032183
[6] GoodRx pricing data (Jan 2025). https://www.goodrx.com/zepbound