What's the Difference Between Semaglutide and Tirzepatide? (October 2026)

01 · The short answer

Which one suits whom?

Neither is simply "better" for everyone. Both are effective, licensed treatments, and which suits you depends on your health profile, tolerance and prescriber advice, not the headline number alone.¹⁵ In SURMOUNT-5, the first large head-to-head trial, tirzepatide produced the larger average loss. A prescriber may still choose semaglutide for individual reasons, so the decision belongs in a consultation.

02 · Side by side

Tirzepatide vs semaglutide at a glance

You can see current Mounjaro pen prices or the Wegovy pen. Every later Mounjaro order is £25 off the standard price (code DOSE25).

03 · Deciding

What your prescriber will weigh up

Your prescriber considers your health history, previous medicines, how you tolerate side effects and your goals. For a closer look, see our guides to the Wegovy and Mounjaro difference and tirzepatide against semaglutide. You can start a free consultation reviewed by a GPhC-registered prescriber.

Related guides: Semaglutide & Tirzepatide Discount Code UK and Difference between semaglutide and tirzepatide.

04 · Trial results

What the trials show

In SURMOUNT-5, 751 adults took tirzepatide or semaglutide 2.4mg for 72 weeks. At least 10% of body weight was lost by 81.6% on tirzepatide versus 60.5% on semaglutide; at least 20% by 48.4% versus 27.3%.¹⁵

Each medicine also has its own trial. In SURMOUNT-1, tirzepatide users lost on average 15% on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks, versus 3.1% with lifestyle changes alone.² In STEP 1, semaglutide 2.4mg users lost on average 14.9% over 68 weeks versus 2.4% on placebo.⁹ These are trial averages; individual results vary, and treatment works alongside a reduced-calorie diet and more physical activity.

05 · Side effects and safety

Side effects and safety

Most Mounjaro side effects are digestive. Nausea, diarrhoea, vomiting, constipation and abdominal discomfort affect more than 1 in 10 people, and they are most likely when starting or moving up a dose, easing within days to a few weeks for most.¹³ In STEP 1, gastrointestinal side effects were reported by 74.2% of people on semaglutide 2.4mg versus 47.9% on placebo, and 7.0% stopped because of side effects.⁹

Serious side effects are uncommon but need urgent attention. Seek immediate medical help for severe, persistent stomach pain that may spread to your back, with or without vomiting (possible pancreatitis); pain in the upper right abdomen, fever or yellowing of the skin or eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing.¹

Mounjaro slows stomach emptying, which can reduce how well oral contraceptive pills are absorbed. Switch to a non-oral method, or add a barrier method, for 4 weeks after starting and for 4 weeks after each dose increase.⁷

06 · Switching and licensing

Switching and licensing

There is no licensed direct conversion between semaglutide and tirzepatide. Switching is done under prescriber supervision: typically the previous medicine is stopped, a washout interval observed, and Mounjaro started at a dose your prescriber judges appropriate. Never run two GLP-1 medicines together.¹

Ozempic is semaglutide licensed for type 2 diabetes, so using it for weight loss is off-label. The licensed weight-management options are Mounjaro and Wegovy, and a regulated UK pharmacy will not supply Ozempic for weight loss.¹⁸ More detail is in our guide to the Mounjaro and semaglutide difference.

07 · NHS access

NHS access

Mounjaro is available on the NHS, but access is being phased in over several years. NICE recommends it for adults with a BMI of at least 35 plus at least one weight-related condition, and the primary-care rollout began in June 2025 with the highest-need groups first.⁴ Many people who meet the licensed criteria choose regulated private treatment rather than waiting. See all weight loss treatments.