If Semaglutide Stops Working, Should You Switch to Tirzepatide? (October 2026)

01 · The short answer

Should you switch? The honest verdict

Switching can make sense if you have been on the highest tolerated semaglutide dose and progress has stalled. It is not an assured fix, and no trial has shown that tirzepatide works in people who did not respond to semaglutide. Both are effective, licensed treatments; the right one depends on your health profile, tolerance and prescriber advice.¹⁵

These are trial averages from one head-to-head study; individual results vary.¹⁵ You can read our related guide on not losing weight on semaglutide.

02 · Before you decide

What to check before you switch

Check whether this is a plateau first. Plateaus of a few weeks are normal as the body adapts. Review food intake honestly, protect protein and activity, check sleep and alcohol, and ask your prescriber whether a dose step-up is appropriate.¹ Never double doses or add unlicensed products.

If you want to explore the option, you can start a free consultation and a GPhC-registered prescriber will review your history. Our Mounjaro pen comes in all six doses, which are in stock; new customers save £40 on their first order with code FIRST40.

Related guide: What to do when mounjaro stops working.

Related guide: I'm on mounjaro.

03 · How switching works

How switching works in practice

There is no licensed direct conversion between semaglutide and tirzepatide. Typically the previous medicine is stopped, a washout interval is observed, and Mounjaro is started at a dose your prescriber judges appropriate, often 2.5mg and sometimes adjusted based on your history.¹⁸

Never run two GLP-1 medicines together, and do not alternate them. Mounjaro must also not be combined with unlicensed research peptides or compounded copies, which have no safety data and no regulated supply chain.¹ Milligram doses are not interchangeable: 2.5mg of tirzepatide is not equivalent to any semaglutide dose, because they are different medicines.

04 · What the evidence says

What the evidence says

In SURMOUNT-5, 751 adults took tirzepatide or semaglutide 2.4mg for 72 weeks. At least 15% of body weight was lost by 64.6% on tirzepatide versus 40.1% on semaglutide.¹⁵ In STEP 1, adults on semaglutide 2.4mg lost on average 14.9% over 68 weeks versus 2.4% on placebo.⁹

In SURMOUNT-1, average loss was 15% on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks.² Treat these as averages across trial groups. Early progress on a new medicine is also modest, so judge it over months, not days. See also what to do if Mounjaro stops working.

05 · Side effects and drawbacks

Drawbacks to weigh up

Both medicines cause gastrointestinal side effects, and starting a new one means a fresh adjustment period. In STEP 1, 74.2% on semaglutide 2.4mg reported gastrointestinal effects versus 47.9% on placebo, and 7.0% stopped because of side effects.⁹ In SURMOUNT-1, 4.3% on 5mg, 7.1% on 10mg and 6.2% on 15mg stopped for side effects versus 2.6% on placebo.²

Stopping any of these medicines is a decision to plan: in SURMOUNT-4, people who stopped tirzepatide regained on average 14% of body weight over the following year.¹⁴ Our guide on switching from Mounjaro to semaglutide covers the other direction.

06 · Serious side effects

Serious side effects: when to get help straight away

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 skin/eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing. If you take insulin or a sulfonylurea alongside Mounjaro, watch for low blood sugar (shakiness, sweating, confusion) — your prescriber may need to adjust those medicines.¹