Every GLP-1 label starts below its effective dose: tirzepatide at 2.5 mg and injected semaglutide at 0.25 mg once weekly, each for four weeks, according to the Zepbound label on DailyMed and the Wegovy label (both read 2026-11-03). Those two numbers answer most versions of the question. This page sets out every current US starting dose by label, the reason each label gives, what a "starting dose" means for a compounded or research vial that has no label, and what retatrutide's trials started at. It reports what the labels and trials state; it recommends no dose.
The full escalation ladders are on the Zepbound dose chart and the Wegovy dose chart; where each ladder ends is on the maintenance doses each label names.
Starting doses, by label
| Product (label effective) | Molecule, route | Starting dose | Time at it | What the label says about it |
|---|---|---|---|---|
| Zepbound (2026-08-28) | tirzepatide, weekly injection | 2.5 mg | 4 weeks | "for treatment initiation and is not approved as a maintenance dosage" |
| Mounjaro (2026-07-29) | tirzepatide, weekly injection | 2.5 mg | 4 weeks | "for treatment initiation and is not intended for glycemic control" |
| Wegovy injection (2026-06-18) | semaglutide, weekly injection | 0.25 mg | weeks 1–4 | Escalation "to reduce the risk of gastrointestinal adverse reactions" |
| Ozempic (2026-07-30) | semaglutide, weekly injection | 0.25 mg | 4 weeks | Same reason; then 0.5 mg |
| Wegovy tablets (2026-06-18) | semaglutide, daily tablet | 1.5 mg | 30 days | Then 4, 9 and 25 mg at 30-day steps |
| Rybelsus (2026-01-30) | semaglutide, daily tablet | 3 mg | 30 days | "this dosage is not effective for glycemic control" |
| Ozempic tablets (2026-01-30) | semaglutide, daily tablet | 1.5 mg | 30 days | Same wording as Rybelsus |
Three things stand out. Every label starts at a dose it does not count as a treatment dose. Every label gives the same reason, gastrointestinal tolerance, and none gives a weight or glucose target for the first month. And the two semaglutide tablets start at different milligram figures for the same molecule: the Rybelsus label states that Rybelsus and Ozempic tablets "are not substitutable on a mg-to-mg basis", so a milligram figure only means something inside its own product.
How long the starting dose lasts
All four injection labels hold the starting dose for four weeks. Zepbound and Mounjaro then move to 5 mg and allow further 2.5 mg steps "after at least 4 weeks on the current dose". Wegovy moves through 0.5, 1 and 1.7 mg at four-week intervals and reaches its maintenance dose at week 17, and adds that if a dose is not tolerated during escalation, delaying the next step by four weeks may be considered. The tablets use 30-day steps. Nothing in any label shortens the first step.
Compounded and research vials
A compounded or research-market vial has no label, so it has no starting dose of its own. What circulates for compounded tirzepatide and semaglutide is the branded label's figure, 2.5 mg or 0.25 mg, written as a volume or as syringe units on the pharmacy's or seller's sheet. The units depend entirely on the concentration of that vial. For a vial, units on a U-100 syringe = milligrams ÷ concentration in mg/mL × 100:
| Starting amount | 2.5 mg/mL | 5 mg/mL | 10 mg/mL | 20 mg/mL | 25 mg/mL |
|---|---|---|---|---|---|
| Tirzepatide 2.5 mg | 100 units | 50 | 25 | 12.5 | 10 |
| Semaglutide 0.25 mg | 10 | 5 | 2.5 | 1.25 | 1 |
| Retatrutide 2 mg (trial start) | 80 | 40 | 20 | 10 | 8 |
The semaglutide row shows the arithmetic's practical edge: at 10 mg/mL and above, 0.25 mg falls between the unit marks of a U-100 syringe, so the lower concentrations are the ones at which the starting amount lands on a whole mark. The full tables are on tirzepatide units and semaglutide units, and how a unit mark relates to millilitres is on insulin syringe units.
"Lowest dose" and "low dose"
The lowest labelled strength of each product is its starting dose: 2.5 mg for tirzepatide, 0.25 mg for weekly semaglutide. Amounts below those are outside every label. That practice is sold as microdosing and is covered, with what has and has not been tested, on tirzepatide microdosing and GLP-1 microdosing.
Retatrutide: a trial start, not a label
Retatrutide has no approval. Eli Lilly's release of 2026-05-21 on TRIUMPH-1 states that participants "initiated treatment with 2 mg once weekly and increased the dose in a step-wise approach every four weeks" to an assigned 4, 9 or 12 mg; its release of 2026-07-23 describes the same 2 mg start for TRIUMPH-2 and TRIUMPH-3. The phase 2 obesity trial (NCT04881760, 338 adults) compared escalation from 2 mg with escalation from 4 mg, and reported that gastrointestinal events were partly mitigated by the lower starting dose (Jastreboff et al., NEJM 2023, PMID 37366315). The full set of trial ladders is on the retatrutide dose schedule.
What is not established
Whether a slower start than the label's reduces side effects further has not been tested against the label schedule in a published trial of these products. How the starting dose behaves on a compounded vial whose content has not been independently verified is unknown by definition. Medibact's tirzepatide guide, semaglutide guide and retatrutide guide cover the compounds. Decisions about any dose belong with the prescriber.
Sources and dates
Opened 2026-11-03: the openFDA label records for ZEPBOUND (set id 487cd7e7-434c-4925-99fa-aa80b1cc776b, effective 2026-08-28), MOUNJARO (0818426a-53eb-4db7-9609-bbae1e7a3964, effective 2026-07-29), OZEMPIC injection (42bdd912-2393-44c4-b7e0-47672ca28991, effective 2026-07-30) and RYBELSUS / OZEMPIC tablets (27f15fac-7d98-4114-a2ec-92494a91da98, effective 2026-01-30), section 2; the DailyMed SPL of WEGOVY (ee06186f-2aa3-4990-a760-757579d8f77b, effective 2026-06-18), sections 2.2 and 2.3; Eli Lilly's TRIUMPH releases of 2026-05-21 and 2026-07-23 (PR Newswire); the abstract of PMID 37366315 through NCBI E-utilities; the ClinicalTrials.gov record NCT04881760. Unit arithmetic by this site. Corrections go to the contact page.