Semaglutide vs Tirzepatide: What the Clinical Trials Actually Show

The Head-to-Head Trial (SURMOUNT-5)

SURMOUNT-5 enrolled 751 adults with obesity (BMI 30 or higher) and no type 2 diabetes. Participants were randomized to receive either tirzepatide or semaglutide at their maximum tolerated doses for 72 weeks. The trial was open-label, meaning both patients and doctors knew which medication they were taking.

The difference was 6.5 percentage points. For someone weighing 220 lbs, that translates to roughly 14 additional pounds lost with tirzepatide over the same period.

One important detail often overlooked is that fewer participants dropped out due to GI side effects on tirzepatide (2.7%) compared to semaglutide (5.6%). This matters because nausea and vomiting are the most common reasons people stop GLP-1 medications.

A follow-up analysis published in the European Heart Journal Open found tirzepatide also showed greater 10-year cardiovascular disease risk reduction in the same patient group.

How They Work

The fundamental difference between these medications is what they target in your body.

Semaglutide (Wegovy®, Ozempic®)

Semaglutide is a GLP-1 receptor agonist. It mimics a single hormone called GLP-1 (glucagon-like peptide-1) that your gut naturally produces after eating. GLP-1 slows gastric emptying, which means food stays in your stomach longer. It also signals fullness to your brain and helps keep blood sugar in check. The medication amplifies these effects so they last longer and hit harder than what your body produces on its own.

Tirzepatide (Zepbound®, Mounjaro®)

Tirzepatide is a dual GIP/GLP-1 receptor agonist, the first in its class. It targets two hormones instead of one, GLP-1 (the same one semaglutide targets) and GIP (glucose-dependent insulinotropic polypeptide). Research published in JCI Insight shows this dual mechanism improves insulin sensitivity and beta-cell function beyond what GLP-1 alone achieves.

Interestingly, tirzepatide actually binds to the GLP-1 receptor with about 5 times weaker affinity than native GLP-1.⁷ Its stronger effects appear to come from the combined action of both pathways working together, rather than from hitting GLP-1 harder.

Weight Loss Results from Clinical Trials

Beyond the head-to-head trial, both medications have been studied extensively in their own trial programs. These numbers come from the largest trials in each program.

Semaglutide (The STEP Trials)

The STEP program enrolled nearly 5,000 participants across multiple trials. In STEP 1 (1,961 participants, 68 weeks), semaglutide 2.4 mg produced an average weight loss of 14.9% compared to 2.4% on placebo. Half of participants lost 15% or more of their body weight.

The longest data comes from STEP 5, which followed participants for 2 full years. At 104 weeks, average weight loss was 15.2%, and 77% of participants lost at least 5% of their body weight. Weight loss was sustained over the full study period without regain while on medication.

Tirzepatide (The SURMOUNT Trials)

SURMOUNT-1 was the largest trial, enrolling 2,539 participants over 72 weeks. At the highest dose (15 mg), the on-treatment analysis showed an average weight loss of 22.5%. Nearly 40% of participants at that dose lost 25% or more of their body weight, a result approaching what bariatric surgery typically achieves.

*STEP and SURMOUNT trials reported response rates at different weight-loss thresholds, so not all rows compare the same cutoff. The numbers above come from each trial's primary NEJM publication. Average weight loss figures reflect the on-treatment (efficacy) estimand.

These are averages from controlled trials. Individual results vary based on starting weight, medication adherence, dietary changes, exercise, and other health factors. Some participants in both programs lost significantly more than the average, and others lost less.

What About Weight Regain?

A January 2026 Oxford/BMJ meta-analysis of 37 studies (over 9,000 adults) found that people who stop GLP-1 medications regain weight at about 0.8 kg (1.8 lbs) per month. At that rate, most people return to their pre-treatment weight within about 18 months.

SURMOUNT-4 showed this directly: participants who switched from tirzepatide to placebo regained 14% of their body weight over 52 weeks, while those who continued lost an additional 5.5%. A follow-up analysis found that 82.5% of those who stopped regained at least 25% of the weight they had lost.

This is one of the most important findings for anyone considering these medications. Current evidence suggests they work best as long-term treatment, similar to medications for blood pressure or cholesterol. Stopping typically means regaining.

Side Effects From the Trials

GI side effects are the most common issue with both medications. Most occur during dose escalation (the first few months while your body adjusts) and tend to decrease over time. Where they differ most is tolerability. Semaglutide at its weight-loss dose appears to cause more nausea and vomiting than tirzepatide at its weight-loss dose.

Side effect data for semaglutide comes from the Wegovy FDA prescribing information and STEP 1-3 pooled analysis. Tirzepatide data comes from SURMOUNT-1 GI tolerability analysis and the Zepbound FDA prescribing information.

Managing Side Effects

Clinical guidelines recommend a "start low, go slow" approach. Both medications begin at lower doses and increase gradually. If nausea persists at a particular dose, providers can extend the time at that dose before increasing. Eating smaller meals and staying hydrated helps. Cutting back on greasy or spicy foods during the adjustment period makes a difference too. Some providers prescribe anti-nausea medication during the adjustment period.

Other Safety Considerations

Both medications carry a boxed warning about thyroid C-cell tumors based on findings in rodent studies. A systematic review of 10 clinical trials involving over 14,500 human participants found less than 1% developed any thyroid cancer, with no evidence of a causal link. The European Medicines Agency reviewed the same data and found "no evidence to suggest a causal relationship." However, both medications are contraindicated in patients with a personal or family history of medullary thyroid carcinoma (MTC).

Gallbladder issues are more clearly associated with GLP-1 medications. A JAMA Internal Medicine meta-analysis found a 37% higher relative risk of gallbladder disease. Rapid weight loss itself increases gallstone risk regardless of the method, so this may be partially related to the amount of weight lost rather than the medication directly.

The Suicide Question Is Resolved

On January 13, 2026, the FDA requested manufacturers remove the suicidal ideation warning from GLP-1 medication labels. Their review analyzed 91 placebo-controlled trials involving nearly 108,000 patients and found no increased risk of suicidal thoughts or behavior. A separate analysis using the FDA Sentinel System (over 2.2 million patients) confirmed the finding. If this concern delayed your decision, the evidence is now clear.

What They Actually Cost

List prices for both medications are over $1,000 per month. But very few people pay list price. Manufacturer savings programs, insurance coverage, and compounded alternatives all change the math significantly.

If you have commercial insurance that covers either medication, the out-of-pocket cost is similar. The bigger difference shows up for people paying cash. Semaglutide through NovoCare runs $199-$349/month, while Zepbound through LillyDirect is $299-$449/month. The oral Wegovy pill (approved December 2025) adds another option at $149-$299/month through NovoCare.

Without insurance, annual cost at maintenance doses runs roughly $4,200 for brand-name semaglutide injection and $5,400 for brand-name tirzepatide injection. These are manufacturer self-pay programs, not list prices.

What Each Medication Is FDA-Approved For

This is where semaglutide has a significant advantage. It has been on the market longer and has more approved uses.

The cardiovascular risk reduction approval for semaglutide is based on the SELECT trial, which enrolled 17,604 patients and found a 20% reduction in major cardiovascular events (heart attack, stroke, cardiovascular death). This is the largest GLP-1 outcomes trial completed to date.

Tirzepatide has its own unique approval: it is the first medication ever approved by the FDA for obstructive sleep apnea in adults with obesity. The SURMOUNT-OSA trial showed up to a 58.7% reduction in the apnea-hypopnea index.¹²

For someone whose primary concern is weight loss, both are FDA-approved for that purpose. But if you also have cardiovascular risk, kidney disease, or liver disease, semaglutide has the broader evidence base. If sleep apnea is a concern, tirzepatide has the specific approval.

Which Medication Fits Your Situation

Your doctor will make the final prescribing decision based on your health history, other medications, insurance coverage, and individual needs. But this framework can help you think about the question before that conversation.

Insurance coverage often narrows the choice. Your plan might cover one medication but not the other, or require trying semaglutide first (step therapy) before approving tirzepatide. If cost is the primary constraint and you are paying out of pocket, semaglutide currently has more affordable access points through NovoCare and the new oral pill.

Neither medication is a standalone solution. Clinical trials that produced these results included dietary counseling and activity recommendations. The medication reduces appetite and helps with adherence, but the lifestyle component matters for long-term outcomes.

The Bottom Line

Before SURMOUNT-5 published in May 2025, every comparison between these medications was indirect. Now there is head-to-head data, and the weight loss difference is real. Tirzepatide produced 20.2% average weight loss compared to 13.7% for semaglutide over the same 72 weeks, with tirzepatide also showing lower GI dropout rates.¹

That does not make tirzepatide the automatic choice. Semaglutide has proven cardiovascular risk reduction from the SELECT trial (17,604 patients)⁶ and five more FDA-approved indications. It's also the only one with an oral pill option, and cash-pay pricing runs lower through NovoCare ($199-$349/mo vs $299-$449/mo through LillyDirect). Insurance coverage and step therapy requirements often narrow the decision further.

A provider who knows your full medical picture and insurance situation can weigh these tradeoffs with you. This guide gives you the clinical data to walk into that conversation informed.

How We Researched This Guide

All clinical data in this guide comes from peer-reviewed studies published in medical journals (the New England Journal of Medicine, JAMA, Nature Medicine, and the BMJ) or from FDA prescribing information and safety communications. We link directly to each source so you can verify the data yourself.

Pricing data comes from manufacturer programs (NovoCare for Novo Nordisk, LillyDirect for Eli Lilly) and is verified against current published rates. We note expiration dates for promotional pricing and update this page when rates change. Non-FDA-approved compounded medication pricing reflects current ranges from telehealth providers we have reviewed. The clinical trial data and FDA approvals discussed in this guide apply only to the brand-name medications studied in those trials, not to compounded versions.

Our editorial team wrote this guide and fact-checked it against primary sources. We update it when new clinical data, FDA decisions, or pricing changes are published.

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Article History

• March 23, 2026: Updated SURMOUNT-1 weight loss data to reflect the primary NEJM-published result (22.5% at 15mg). Corrected trial comparison table thresholds. Verified all pricing against current NovoCare and LillyDirect rates. Added medical disclaimer and methodology section.
• March 5, 2026: Verified NovoCare and LillyDirect pricing still current. Confirmed oral Wegovy 4mg introductory pricing ($149/mo) through April 15, 2026.
• February 27, 2026: Added SURMOUNT-5 cardiovascular follow-up analysis from European Heart Journal Open. Updated compounded medication regulatory context.
• February 25, 2026: Original publication with SURMOUNT-5 head-to-head data, STEP and SURMOUNT trial program results, and cost comparison.

Sources

1. Aronne LJ, Sattar N, Horn DB, et al. Tirzepatide vs semaglutide for weight reduction (SURMOUNT-5). N Engl J Med. 2025.
2. Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med. 2021;384(11):989-1002.
3. Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). N Engl J Med. 2022;387(3):205-216.
4. Garvey WT, Frias JP, Jastreboff AM, et al. Two-year effects of semaglutide in adults with overweight or obesity (STEP 5). Nat Med. 2022;28(10):2083-2091.
5. Aronne LJ, Sattar N, Horn DB, et al. Continued treatment with tirzepatide for maintenance of weight reduction (SURMOUNT-4). JAMA. 2024;331(1):38-48.
6. Lincoff AM, Brown-Frandsen K, Colhoun HM, et al. Semaglutide and cardiovascular outcomes in obesity (SELECT). N Engl J Med. 2023;389(24):2221-2232.
7. Thomas CE, et al. Mechanism of action differences between semaglutide and tirzepatide. JCI Insight. 2020.
8. FDA Drug Safety Communication. Update on evaluation of suicidal thoughts with GLP-1 RAs. January 13, 2026.
9. West S, Scragg J, Aveyard P, et al. Weight regain following cessation of medication for weight management: systematic review and meta-analysis. BMJ. 2026;388:e085304.
10. He L, et al. GLP-1 RAs and gallbladder disease: systematic review. JAMA Intern Med. 2022.
11. Alkhezi OS, et al. Thyroid cancer risk with semaglutide: systematic review. 2024.
12. Malhotra A, Grunstein RR, et al. Tirzepatide for the treatment of obstructive sleep apnea (SURMOUNT-OSA). N Engl J Med. 2024;391(14):1288-1298.