GLP1 MathSemaglutide to tirzepatide conversion
There is no official mg-to-mg conversion between semaglutide and tirzepatide. They are different molecules with different dose ranges. What people call a "conversion chart" is really a comparison of the labeled dose steps.
How the labeled dose steps line up
| Step | Semaglutide (Wegovy label) | Tirzepatide (Zepbound label) |
|---|---|---|
| Starting dose | 0.25 mg weekly | 2.5 mg weekly |
| Step 2 | 0.5 mg | 5 mg |
| Step 3 | 1 mg | 7.5 mg |
| Step 4 | 1.7 mg | 10 mg |
| Step 5 | 2.4 mg (maintenance) | 12.5 mg |
| Step 6 | — | 15 mg (maximum) |
Each step on both labels lasts at least 4 weeks. Being on step 3 of one medicine does not mean you "should" be on step 3 of the other.
What prescribers usually do when switching
Most prescribers do not match steps. When switching from semaglutide to tirzepatide, the common approach is to start tirzepatide at 2.5 mg (the labeled starting dose) and step up every 4 weeks as tolerated, because the stomach side effects are new to your body even if you tolerated semaglutide. Some prescribers start higher for patients already on a high semaglutide dose. That is a judgment call for your prescriber, not a formula.
Why the numbers look so different
Tirzepatide doses are 10 to 20 times the mg of semaglutide doses. That is not "more medicine"; it is a different medicine with a different potency per milligram. Comparing 1 mg of semaglutide to 1 mg of tirzepatide means nothing.
Units change too
If you draw from vials, the units also change because the vial strengths differ. Use the tirzepatide calculator with your new vial's mg/mL rather than carrying over the units you used for semaglutide.