The caveat that governs this page
Retatrutide is not approved anywhere, so there is no approved dose. What follows is a description of the regimens that clinical trials used, taken from their published reports, so that readers can interpret the headline numbers correctly — “24% weight loss” means something specific about dose, escalation and duration. It is not a dosing chart, not a recommendation, and not instructions for use. Material sold online as retatrutide is unlicensed and of unverified content, and nothing here applies to it.
Phase 2 obesity trial (NEJM 2023): six retatrutide arms
The 48-week obesity trial randomised 338 adults (BMI ≥30, or ≥27 with a weight-related condition) in a 2:1:1:1:1:2:2 ratio to placebo or to once-weekly subcutaneous retatrutide at maintenance doses of 1 mg, 4 mg (started at 2 mg), 4 mg (started at 4 mg), 8 mg (started at 2 mg), 8 mg (started at 4 mg) or 12 mg (started at 2 mg). Escalation to the maintenance dose took place over the first weeks, and the two starting doses were included specifically to test whether a gentler start reduced gastrointestinal events — it did. The primary endpoint was percentage weight change at 24 weeks; 48 weeks was a secondary endpoint.
| Maintenance dose | Starting dose | 24 weeks | 48 weeks |
|---|---|---|---|
| Placebo | — | −1.6% | −2.1% |
| 1 mg | 1 mg | −7.2% | −8.7% |
| 4 mg | 2 mg or 4 mg (pooled) | −12.9% | −17.1% |
| 8 mg | 2 mg or 4 mg (pooled) | −17.3% | −22.8% |
| 12 mg | 2 mg | −17.5% | −24.2% |
Phase 2 type 2 diabetes trial (Lancet 2023): seven arms plus dulaglutide
The 36-week diabetes trial randomised 281 adults with HbA1c 7.0–10.5% to placebo, dulaglutide 1.5 mg weekly as an active comparator, or retatrutide at 0.5 mg, 4 mg (started at 2 mg), 4 mg (no escalation), 8 mg (started at 2 mg), 8 mg (started at 4 mg) or 12 mg (started at 2 mg), all once weekly. The primary endpoint was HbA1c change at 24 weeks. At 36 weeks the highest dose produced HbA1c reductions of up to about 2 percentage points and weight loss of about 17%, both exceeding dulaglutide.
Phase 3 TRANSCEND-T2D-1 (Lancet 2026): 4, 9 and 12 mg
The first full phase 3 report randomised 537 adults with type 2 diabetes inadequately controlled by diet and exercise (HbA1c 7.0–9.5%, BMI ≥23) 1:1:1:1 to placebo or retatrutide 4 mg, 9 mg or 12 mg once weekly for 40 weeks — note the 9 mg step replacing phase 2's 8 mg. HbA1c fell by 1.69, 1.86 and 1.94 percentage points versus 0.81 with placebo, and body weight by 11.5%, 13.9% and 15.3% versus 2.6%. Discontinuation for adverse events was 2–5%. The obesity phase 3 programme (TRIUMPH) uses the same dose range; its full publications were pending as of September 2026.
| Arm | HbA1c change | Weight change |
|---|---|---|
| Placebo | −0.81 pts | −2.6% |
| 4 mg weekly | −1.69 pts | −11.5% |
| 9 mg weekly | −1.86 pts | −13.9% |
| 12 mg weekly | −1.94 pts | −15.3% |
Why the trials escalate
Every incretin drug is titrated because gastrointestinal side effects track the rate of dose increase more than the final dose: the gut adapts over weeks. Retatrutide's phase 2 design turned this into a formal comparison by giving the same maintenance dose with two different starting doses, and the 2 mg start produced fewer early nausea and vomiting events than the 4 mg start at the same 48-week weight loss. Approved products encode the same principle — tirzepatide starts at 2.5 mg and rises in 2.5 mg steps every four weeks; semaglutide for weight management escalates over 16 weeks.
Milligrams, micrograms, millilitres and units
Trial doses are stated in milligrams of peptide delivered once a week. Reading them requires no arithmetic because trial drug is supplied in pre-filled pens at fixed concentrations. The arithmetic questions people search for — “how much bacteriostatic water for a 10 mg vial”, “how many units is 4 mg” — arise only with lyophilised powder, which is how unlicensed material is sold. The relationship is simple: concentration equals peptide mass divided by diluent volume (10 mg in 2 mL is 5 mg/mL), and on a U-100 insulin syringe 100 units equals 1 mL, so volume in units equals volume in mL multiplied by 100. The calculator below does exactly that arithmetic and nothing more.
What this guide deliberately does not contain
There is no recommended dose, escalation schedule or duration here, because none exists outside a clinical trial protocol reviewed by an ethics committee and supervised by investigators. The reconstitution and bacteriostatic-water guides explain the chemistry of preparing peptide solutions in a laboratory context. The side-effects guide explains why escalation matters clinically. The retatrutide profile covers status: not approved anywhere as of September 2026, with a US filing planned for early 2027 and a pre-approval expanded-access programme opened in August 2026 for a defined patient group.
Reconstitution calculator
Enter how much peptide is in the vial and how much diluent (e.g. bacteriostatic water) is added. The tool returns the resulting solution concentration — and, for any amount you type, the volume it corresponds to. This is educational arithmetic, not a dosing recommendation.
Enter an amount to see the volume it corresponds to.
Educational concentration mathematics only. This tool does not recommend a dose, amount, or protocol, and nothing here is medical advice. Many peptides are not authorized by Health Canada for human use — see our reconstitution and bacteriostatic-water guides for context.
Sources and what they cover
These primary studies, official records and standards cover the topics linked below. The scope notes distinguish laboratory findings, human trials and regulatory records. This is a selected bibliography, not a systematic review or verification of every sentence; absence of a study here does not prove that no study exists.
- Jastreboff et al. (2023) — Retatrutide for obesity, phase 2 trial
Phase 2 obesity trial: studied regimens, weight and adverse events. Trial doses are not instructions for personal use.
Relevant sections: Phase 2 obesity trial (NEJM 2023): six retatrutide arms · Why the trials escalate
- Rosenstock et al. (2023) — Retatrutide in type 2 diabetes, phase 2 trial
Phase 2 diabetes trial; its glycemic endpoints, participants and regimens differ from the obesity study.
Relevant sections: Phase 2 type 2 diabetes trial (Lancet 2023): seven arms plus dulaglutide · Why the trials escalate
- Bajaj et al. (2026) — TRANSCEND-T2D-1, retatrutide phase 3 trial
Published phase 3 diabetes trial; not all phase 3 programs and not a regulatory authorization.
Relevant sections: Phase 3 TRANSCEND-T2D-1 (Lancet 2026): 4, 9 and 12 mg · Why the trials escalate
FAQ
What doses of retatrutide were used in trials?+
Phase 2: 1, 4, 8 and 12 mg once weekly (plus 0.5 mg in the diabetes trial). Phase 3 TRANSCEND-T2D-1: 4, 9 and 12 mg once weekly. All were reached by stepwise escalation.
What starting dose did the retatrutide trials use?+
Most arms started at 2 mg weekly; some started at 4 mg. The 2 mg start reduced early gastrointestinal side effects at the same final weight loss.
How often was retatrutide dosed?+
Once weekly by subcutaneous injection in every trial, consistent with its roughly 6-day half-life.
How much bacteriostatic water for a 10 mg vial?+
That is a concentration choice, not a dose: 10 mg in 1 mL gives 10 mg/mL, in 2 mL gives 5 mg/mL. The calculator on this page computes concentration and the volume any amount corresponds to. It does not recommend an amount.
Is there a retatrutide dosage chart?+
Not an approved one — retatrutide is not approved. The tables on this page list the trial regimens and their results; they describe research protocols, not instructions.