Switching between Mounjaro (tirzepatide) and Wegovy (semaglutide) is a common clinical question. It sounds like a swap. It isn't. Here's what actually happens when you switch, why there's no simple conversion, and what to expect.

Why people switch

  • Tolerability — one medicine suits them better than the other.
  • A plateau on the current medicine.
  • Cost or supply.
  • Semaglutide's licensed cardiovascular indication.
  • Moving to the higher-efficacy option on head-to-head data.

Why there is no direct conversion table

This is important. Tirzepatide (doses of 2.5–15mg) and semaglutide (doses of 0.25–2.4mg) act on different receptor combinations at completely different dose scales. Tirzepatide is a dual GLP-1/GIP agonist; semaglutide is a GLP-1 agonist. A milligram of one is not comparable to a milligram of the other.

Any "conversion chart" circulating online is not a licensed equivalence and should not be used to self-dose. It has not been established by the manufacturer or by regulators, and following it can lead to overshooting tolerance or under-treating.

How a switch actually works

Your prescriber selects an appropriate starting dose on the new medicine based on how long you've been treated, your current dose and your tolerance, then re-titrates upward. If you are well established on the previous medicine, you usually don't restart at the absolute lowest dose — but you also don't jump straight to a dose that "feels equivalent". The point is to land safely on the new drug and then step up as tolerated.

Timing the switch

The previous drug is still in your system for several weeks after your last dose. Your prescriber will time the switch to account for this. See how long Mounjaro stays in your system for the underlying half-life data.

What to expect

  • Some return of gastrointestinal side effects while adjusting to the new medicine.
  • Possibly a brief plateau or small fluctuation in weight during the transition.
  • Appetite suppression may feel different in character, even at a comparable level of effect.

Switching direction matters

Wegovy to Mounjaro is usually motivated by efficacy. Tirzepatide outperformed semaglutide in the head-to-head SURMOUNT-5 trial for weight loss.

Mounjaro to Wegovy is often motivated by tolerability, or by the licensed cardiovascular indication established in the SELECT trial for semaglutide in adults with overweight or obesity and established cardiovascular disease.

Switching between Wegovy formats

Moving between the Wegovy injection and the oral tablet is also a clinical decision with its own titration. See Wegovy pill vs injection.

Switching is a clinical decision, not a maths problem. The two drugs don't map onto each other in a straight line, so re-titration under prescriber guidance is the right approach.

When to see your pharmacist or doctor

  • Never run two GLP-1 medicines at the same time.
  • Never switch without prescriber input.
  • Tell your prescriber exactly when your last dose of the previous medicine was.
  • Report any severe or persistent nausea, vomiting, dehydration or upper abdominal pain during the switch.

Frequently asked questions

Do I restart at the lowest dose? Not usually if you're well established, but not straight to a "feels equivalent" dose either. Your prescriber decides.

How long should I wait between the two? There's no single fixed gap — your prescriber times it based on clearance and tolerance.

Will I regain weight while switching? A brief plateau or small fluctuation is possible; most people continue losing overall.

Which is better? Depends on the goal. Tirzepatide won on weight loss in SURMOUNT-5; semaglutide has the licensed cardiovascular indication from SELECT.

Can I switch back? Yes — with prescriber input and re-titration.

See also Mounjaro vs Wegovy, Wegovy pill vs injection, how long Mounjaro stays in your system, and Mounjaro price comparison UK.

References

  1. Aronne LJ et al. Tirzepatide versus Semaglutide for the Treatment of Obesity (SURMOUNT-5). N Engl J Med 2025.
  2. Lincoff AM et al. Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes (SELECT). N Engl J Med 2023.
  3. Mounjaro (tirzepatide) Summary of Product Characteristics, electronic medicines compendium.
  4. Wegovy (semaglutide) Summary of Product Characteristics, electronic medicines compendium.

Reviewed by Jimah Alsaai MPharm, GPhC 2232652, Superintendent Pharmacist, Solira.