Tirzepatide vs. Semaglutide: How They Differ and Which Works Better

The Short Answer

Tirzepatide produced more weight loss. In SURMOUNT-5, the only trial to test them against each other, 751 adults took one or the other for 72 weeks: tirzepatide averaged 20.2% of body weight lost, semaglutide 13.7%.

That is a real gap and it is not close. It also is not the whole decision. Cost, coverage, side-effect tolerance and what your prescriber can actually get you decide this for most people before efficacy does.

How does each one work?

Both are incretin mimics — lab-made versions of gut hormones that tell your body food has arrived. The difference is how many.

Semaglutide activates one receptor: GLP-1. It reduces hunger by acting on appetite centres in the brain, slows how fast food leaves the stomach, and prompts insulin release when blood sugar is high.

Tirzepatide activates two: GLP-1 and GIP. GIP — glucose-dependent insulinotropic polypeptide — is a second incretin released from a different part of the gut. Its role in appetite and fat metabolism is less completely understood than GLP-1's, but the clinical result of hitting both is more weight loss than hitting one.

Both are peptides engineered to survive for days rather than minutes, which is why both are weekly injections. Neither burns fat, raises metabolism or blocks absorption. The mechanism is appetite, in both cases — which is why appetite returns when either one stops.

What does the head-to-head data actually show?

Most drug comparisons are stitched together from separate trials with different participants, which is a weak way to compare anything. This pair is unusual: they were tested directly.

SURMOUNT-5 randomised 751 adults 1:1 and ran for 72 weeks, titrating each participant to their maximum tolerated dose.

Tirzepatide produced 47% greater relative weight loss. The gap widens as the target gets harder: at the 25% threshold, roughly twice as many people got there.

Three things to hold alongside that.

The trial pushed to maximum tolerated doses — 89.3% of the tirzepatide group took at least one 15 mg dose, and 92.8% of the semaglutide group took at least one 2.4 mg dose. Most people tolerated the top of the range. If you cannot, the comparison shifts.

These are trial conditions, with structured support and monitoring most patients never get. Real-world results are typically lower for both.

And they are averages. Individual response varies enormously in both arms — plenty of people on semaglutide lost more than the tirzepatide average, and plenty on tirzepatide lost less than the semaglutide one.

Their separate trials point the same direction. Semaglutide's STEP 1 followed 1,961 adults for 68 weeks and averaged 14.9% against 2.4% on placebo. Tirzepatide's SURMOUNT-1 followed 2,539 adults for 72 weeks and averaged 22.5% at the 15 mg dose, with 63% of that group losing at least a fifth of their body weight.

How do the side effects compare?

They are more alike than different, and neither is gentle.

Gastrointestinal effects dominate both. Nausea leads, then vomiting, diarrhoea and constipation. They cluster in the first weeks and after each dose increase, and they fade for most people. This is why titration is deliberately slow on both drugs, and why "how fast can I get to the top dose" is the wrong question.

Both carry the same boxed warning for thyroid C-cell tumours, based on rodent studies. Neither should be taken by anyone with a personal or family history of medullary thyroid carcinoma or MEN 2 syndrome. Both have been associated with pancreatitis and with gallbladder problems, the latter partly a known consequence of rapid weight loss itself. Neither should be used in pregnancy.

One difference worth knowing: tirzepatide may reduce the effectiveness of oral contraceptives around dose increases. If that applies to you, it is a conversation to have before starting rather than after.

The honest summary: side effects are not a strong basis for choosing between them in advance, because tolerance is individual and unpredictable. It is, however, a very strong basis for switching — and switching is normal. Fuller detail in Weight Loss Medications Explained.

What does each one cost?

Both manufacturers now sell direct to cash-paying patients at published prices, which has changed this comparison more than anything in the last two years.

Read Lilly's refill condition. The Zepbound prices assume a refill within 45 days of the previous delivery. Miss it and 12.5 mg reverts to $849 a month and 15 mg to $1,049. A holiday, a supply gap or a slow prior authorisation can trigger that.

Eligible Medicare beneficiaries can pay $50 a month for either through the CMS Medicare GLP-1 Bridge, which runs from July 1, 2026 to December 31, 2027.

Telehealth platforms bundle a clinician and coaching on top and run $99 to $548 a month across the providers we track. Full breakdown in the GLP-1 Price Guide, or get a personalised figure from the cost calculator.

Which one can you actually get?

This is the question that decides it more often than the trial data does.

Coverage differs plan by plan, not drug by drug. Some formularies cover one and not the other, and a prior authorisation approved for semaglutide does not transfer. Check your own formulary before you get attached to an answer.

Compounded versions of both have largely gone. The FDA declared the tirzepatide shortage resolved on December 19, 2024 and the semaglutide shortage on February 21, 2025, ending the exemption that allowed pharmacies to mass-produce copies; every wind-down deadline had passed by May 22, 2025. On April 30, 2026 the FDA proposed excluding both from the 503B bulks list, finding "no clinical need" for outsourcing facilities to compound them.

Platforms still advertise compounded versions. In March 2026 the FDA sent warning letters to 30 telehealth companies over compounded GLP-1 marketing, objecting to "claims implying sameness with FDA-approved products" and to firms "obscuring product sourcing by advertising drug products branded with the telehealth firm's name." No companies were named. Ask any provider which pharmacy fills your prescription and on what basis.

There is now a third option neither of these is. Lilly's Foundayo (orforglipron) was approved on April 1, 2026 — a once-daily pill with no food or water timing restrictions, from $149 a month direct. Average loss at the highest dose was 27.3 pounds, or 12.4%, which is below both injectables. If the weekly injection is what has been stopping you, that trade is now available.

Which is right for you?

Tirzepatide, if efficacy is the deciding factor. It produced more weight loss head-to-head, by a margin that widens at the harder thresholds. If you can get it and afford it and tolerate it, the data points one way.

Semaglutide, in more cases than the headline suggests:

• Your plan covers it and not tirzepatide. A covered drug beats a better drug you are paying cash for, most of the time.
• You want the oral option. Semaglutide has a tablet form; tirzepatide does not.
• You tolerated it and not tirzepatide. Real tolerance beats trial averages every time.
• The 45-day refill condition worries you. If your supply or schedule is unpredictable, semaglutide's pricing has no equivalent cliff.
• You want the longest track record. Semaglutide has been studied longer and in more people, including large cardiovascular outcome data. That matters more to some people than a few percentage points.

Either, and switch if it isn't working. Neither choice is permanent. Starting on the one you can get today and moving later is a completely ordinary path, and a prescriber who treats the first choice as final is not doing the job.

Read the full semaglutide guide or the tirzepatide guide, compare providers that prescribe each, or work out your own cost with the calculator.

Sources

• Eli Lilly — Zepbound showed superior weight loss over Wegovy in complete SURMOUNT-5 results — May 11, 2025; 751 participants, 72 weeks, 20.2% vs 13.7% and all threshold figures above.
• Eli Lilly — SURMOUNT-1 results published in NEJM — 2,539 participants, 72 weeks, 22.5% at 15 mg.
• Novo Nordisk — STEP 1 trial results — 1,961 adults, 68 weeks, 14.9% vs 2.4%.
• Eli Lilly — Lilly lowers the price of Zepbound single-dose vials — December 1, 2025, per-dose prices and the 45-day refill condition.
• Novo Nordisk / NovoCare — Wegovy self-pay price guide (PDF)
• Eli Lilly — FDA approves Foundayo (orforglipron) — April 1, 2026.
• FDA — FDA clarifies policies for compounders as national GLP-1 supply begins to stabilize
• FDA — FDA Proposes to Exclude Semaglutide, Tirzepatide, and Liraglutide on 503B Bulks List — April 30, 2026.
• FDA — FDA warns 30 telehealth companies against illegal marketing of compounded GLP-1s — March 3, 2026.
• CMS — Medicare GLP-1 Bridge
• Side effect, boxed warning, pregnancy and oral-contraceptive statements are drawn from the FDA prescribing information for Wegovy, Ozempic, Zepbound and Mounjaro.

*Every dated claim above was verified against the source linked beside it on the date shown at the top of this guide. This is not medical advice — talk to a licensed clinician before starting or changing any treatment.*