Switching from semaglutide to tirzepatide

Is there a semaglutide to tirzepatide dose conversion?

No. There's no validated dose equivalence between semaglutide and tirzepatide, because the two medicines work on a different mix of receptors¹. Neither the Mounjaro nor the Zepbound label includes a conversion from semaglutide or any other GLP-1 medicine^2–3.

Charts online that say a certain semaglutide dose "equals" a certain tirzepatide dose don't come from the labels. The Pharmaceutical Journal's 2026 switching guide says there's little high-quality guidance. Clinicians work from general rules for switching between GLP-1 medicines instead¹.

Why semaglutide mg and tirzepatide mg aren't interchangeable

Semaglutide mg and tirzepatide mg can't be swapped because they are different molecules with different dose ranges. Semaglutide acts on the GLP-1 receptor only, and its labeled doses run from 0.25 mg to 2.4 mg (7.2 mg for some Wegovy patients). Tirzepatide acts on both the GIP and GLP-1 receptors, with doses from 2.5 mg to 15 mg^2,4–5.

Even the same molecule isn't swapped mg for mg. The semaglutide tablet labels say Rybelsus and Ozempic tablets "are not substitutable on a mg-to-mg basis"⁶. The Wegovy label switches people on 2.4 mg weekly injections to 25 mg daily tablets⁴. If mg don't carry over between two forms of semaglutide, they can't carry over to a different medicine.

What starting dose of tirzepatide do the labels give after semaglutide?

The Zepbound label starts every patient on 2.5 mg of tirzepatide once weekly for 4 weeks, then 5 mg. It says the 2.5 mg dose "is for treatment initiation and is not approved as a maintenance dosage"². Mounjaro also starts at 2.5 mg weekly and goes up in 2.5 mg steps after at least 4 weeks³.

• Both labels say to follow the dose increases to reduce the risk of stomach and gut side effects^2–3.
• Neither label has a different starting dose for people who have already taken semaglutide^2–3.
• The Pharmaceutical Journal guide gives the same 2.5 mg start. It warns that straying from the standard dose steps can increase side effects and make the medicine harder to tolerate¹.
• The UK Mounjaro SmPC uses the same schedule: 2.5 mg for 4 weeks, then 5 mg, with 2.5 mg steps after at least 4 weeks⁸.

If your prescriber suggests a different plan, ask them why. Any start other than 2.5 mg is a clinical decision, not something the labels set out.

When to take your first tirzepatide dose after semaglutide

The labels don't set a gap between your last semaglutide dose and your first tirzepatide dose. They say tirzepatide shouldn't be used together with a GLP-1 medicine, and Wegovy says the same about using it with other GLP-1 medicines^2,4.

The Pharmaceutical Journal guide describes two ways prescribers time the switch¹:

• Same-day switch: take the first dose of the new medicine on the day the next dose of the old one would have been due.
• Washout: wait 1 to 2 weeks before the first dose of the new medicine. The guide prefers this for people who are having significant side effects.

Semaglutide leaves the body slowly. The Ozempic label gives a half-life of about 1 week and says semaglutide is present in the blood for about 5 weeks after the last dose⁵. The Wegovy label says about 5 to 7 weeks after the last 2.4 mg or 7.2 mg dose⁴. Tirzepatide's half-life is about 5 days³.

Tirzepatide vs semaglutide: what the head-to-head trial found

In SURMOUNT-5, adults with obesity and without type 2 diabetes lost an average of 20.2% of their body weight on tirzepatide (10 mg or 15 mg) and 13.7% on semaglutide (1.7 mg or 2.4 mg) after 72 weeks⁷. Each person took the highest dose they tolerated.

• 751 people took part, and each was assigned to one medicine for the whole trial⁷. The trial didn't test switching from one to the other.
• Stomach and gut side effects were the most common with both medicines. Most were mild to moderate and happened mainly while the dose was being increased⁷.
• The trial was funded by Eli Lilly, which makes tirzepatide⁷.

The Zepbound label also says most nausea, vomiting and diarrhea happened during dose increases and lessened over time². Starting again at 2.5 mg and stepping up means you go through those dose increases again. Our GLP-1 side effects guide has the label rates by dose.

Switching back from tirzepatide to semaglutide

Going back to semaglutide means starting again at 0.25 mg once weekly, its lowest dose, whatever tirzepatide dose you were on. That's what the Pharmaceutical Journal guide says, with the dose then going up as tolerated¹. That matches the 0.25 mg starting dose in the Ozempic and Wegovy labels^4–5.

• The same two timing options apply: start on the next scheduled dose day, or after a 1 to 2 week washout¹.
• Ozempic goes up after 4 weeks at 0.25 mg. Wegovy steps up every 4 weeks: 0.25 mg, 0.5 mg, 1 mg, 1.7 mg, then 2.4 mg^4–5.
• The Wegovy label says to consider waiting 4 more weeks before the next step if a dose isn't tolerated⁴.

In the UK, Mounjaro is the tirzepatide brand licensed for weight management, and Wegovy is the semaglutide brand^8–9. The UK Wegovy SmPC notes that even switching between semaglutide tablets and injections "cannot easily be predicted"⁹.