"Switching from semaglutide to tirzepatide" is searched as if a conversion chart existed. None does on either label. What exists is a starting dose written for everyone, two switching trials run from other GLP-1 medicines, one small retrospective series on semaglutide itself, a dose-equivalence model funded from one side of the comparison, and one head-to-head trial in which nobody switched. This page sets those out with their dates and what each can and cannot say, and converts the tirzepatide steps into syringe units. It does not describe a switch to make.
The per-compound pages are the semaglutide dosage page and the tirzepatide dosage page; the compounds are covered in Medibact's Semaglutide guide and Tirzepatide guide.
What the labels say, and do not
ZEPBOUND (Eli Lilly, effective 2026-08-28): "The recommended starting dosage of ZEPBOUND for all indications is 2.5 mg injected subcutaneously once weekly for 4 weeks." Increases follow in 2.5 mg steps after at least 4 weeks. The label has no section on patients coming from another GLP-1 medicine, so on its face the starting dose applies to them as to anyone.
WEGOVY (Novo Nordisk, published 2026-06-30): section 2.5 is titled "Switching Between WEGOVY Injection and WEGOVY Tablets". It moves someone on 2.4 mg injection to 25 mg tablets one week after the last injection, and someone on 25 mg tablets to 2.4 mg injection the day after the last tablet. It says nothing about moving to another molecule.
So the one switching instruction in either label is within semaglutide, and the one starting instruction for tirzepatide is written without reference to what came before.
The switching trials that exist
A ClinicalTrials.gov search on 2026-09-23 found no randomised trial of switching from semaglutide to tirzepatide. Eli Lilly registered two switching trials, both in type 2 diabetes:
| Trial | Switched from | Enrolled | Tirzepatide start | Posted result |
|---|---|---|---|---|
| SURPASS-SWITCH, NCT05564039 (randomised, 40 weeks) | Dulaglutide 0.75 or 1.5 mg | 282 | 2.5 mg, +2.5 mg every 4 weeks to 15 mg or maximum tolerated | Weight -11.0 kg vs -3.6 kg on dulaglutide raised to 4.5 mg; HbA1c -1.59 vs -0.69 |
| SURPASS-SWITCH-2, NCT05706506 (single arm, 12 weeks) | A GLP-1 receptor agonist listed in the protocol | 152 | 5 mg from the first week | HbA1c -0.43; weight -2.15 kg |
Two readings. First, the manufacturer itself tested two different starts: the label's 2.5 mg in one trial and 5 mg, skipping the first step, in the other. Second, the registry record for SURPASS-SWITCH-2 does not name which GLP-1 medicines participants came from, and no journal publication of it was found in PubMed on 2026-09-23, so whether any of them came from semaglutide cannot be read from the public record.
The one published series on semaglutide
Kurinami and colleagues (Endocrinol Metab 2025, PMID 41088952) reviewed 15 people with type 2 diabetes in Japan who moved from semaglutide 1.0 mg to tirzepatide because of inadequate weight loss. All restarted at 2.5 mg; 10 were escalated to 7.5 mg and 5 to 10 mg. Over 3 months the 10 mg group's HbA1c fell by 0.7 percentage points (significant) and weight changed by -6.6 kg (not significant, p = 0.07); the 7.5 mg group showed no significant change. The authors suggest earlier escalation to 10 mg. Fifteen people, retrospective, three months: it is the whole published record specific to this switch, and it is a small one.
Equivalence: one model, and who built it
Builes-Montaño and colleagues (Diabetes Ther 2026, PMID 42252377) modelled weight change across 48 phase 3 trial arms of semaglutide and tirzepatide in type 2 diabetes, 16,524 people in total. They estimated a 99.4% probability that semaglutide 2.4 mg and tirzepatide 10 mg are equivalent within ±2 percentage points of weight loss, and 94.8% for semaglutide 7.2 mg against tirzepatide 15 mg; lower semaglutide doses were not equivalent to higher tirzepatide doses. Two of the three authors are employees of Novo Nordisk, which makes semaglutide, and the analysis is of trial averages in diabetes, not of anyone switching. An equivalence in average weight loss at maintenance is not a statement about where a switch should start, and the paper does not make one.
The head-to-head trial, in which nobody switched
SURMOUNT-5 (Aronne et al., NEJM 2025, PMID 40353578) randomised 751 adults with obesity and without diabetes to the maximum tolerated dose of tirzepatide (10 or 15 mg) or semaglutide (1.7 or 2.4 mg) for 72 weeks. Weight change was -20.2% on tirzepatide and -13.7% on semaglutide. The trial was open-label and funded by Eli Lilly. It compares people who started one drug with people who started the other; it says nothing direct about moving from one to the other.
The overlap arithmetic
The WEGOVY label gives semaglutide an elimination half-life of about 1 week and states it is present in the circulation for about 5 to 7 weeks after the last dose of 2.4 mg or 7.2 mg. The ZEPBOUND label gives tirzepatide about 5 to 6 days. By the semaglutide figure, about half of its level remains one week after the last injection, a quarter after two weeks and an eighth after three. Any first tirzepatide dose within that window adds to semaglutide still present. That is arithmetic from the labels' half-lives; no pharmacokinetic study of the overlap was found.
The tirzepatide steps as units
Units on a U-100 syringe = mg ÷ mg/mL × 100.
| Tirzepatide | 5 mg/mL | 10 mg/mL | 20 mg/mL |
|---|---|---|---|
| 2.5 mg | 50 units | 25 units | 12.5 units |
| 5 mg | 100 units | 50 units | 25 units |
| 7.5 mg | 150 units | 75 units | 37.5 units |
| 10 mg | 200 units | 100 units | 50 units |
The approved single-dose pens and vials hold every strength in 0.5 mL, so each is 50 units regardless of milligrams; the multi-dose presentations hold each dose in 0.6 mL, 60 units. A unit figure carried over from a semaglutide vial means nothing for a tirzepatide vial of different concentration, which is the most direct way a switch can go wrong on a syringe. The mg to units page sets out the formula and the tenfold misreadings; the reconstitution calculator's tirzepatide setting works any vial.
What is not established
No randomised trial of switching from semaglutide to tirzepatide was found; no label states a conversion or an interval; the one semaglutide-specific series is 15 people over 3 months; the equivalence model is of trial averages in diabetes and has manufacturer authors. Nothing on this page is a starting dose or a switching plan. Those decisions belong with a prescriber.
Sources and dates
Opened 2026-09-23: the ZEPBOUND label via openFDA (set id 487cd7e7-434c-4925-99fa-aa80b1cc776b, effective 2026-08-28), sections 2, 3 and 12.3; the WEGOVY label via DailyMed (set id ee06186f-2aa3-4990-a760-757579d8f77b, published 2026-06-30), sections 2.2, 2.5 and 12.3; ClinicalTrials.gov v2 records NCT05564039 and NCT05706506 with their posted outcome measures, and the registry searches described above; abstracts via NCBI E-utilities for Kurinami et al. 2025 (PMID 41088952), Builes-Montaño et al. 2026 (PMID 42252377, with its conflict-of-interest statement) and Aronne et al. 2025 (PMID 40353578). Overlap and unit arithmetic by this site. Corrections go to the contact page.