In the phase-2 trial, retatrutide was given as a once-weekly subcutaneous injection, started low and increased every 4 weeks toward a target of 1, 4, 8 or 12 mg. The higher target doses produced the most weight loss in the study — but also the most side effects, which is why the dose is raised gradually rather than all at once.
Below is the trial-reported escalation schedule, a dosage chart, how weight loss varied by dose, and how reconstitution (BAC water) math works — all informational, not dosing instruction.
Retatrutide is an investigational drug. It is not FDA-approved for human use and is not available by prescription. Products sold online as “retatrutide” are labelled for laboratory research only. This page summarizes published clinical-trial data for information — it is not medical advice and not a dosing protocol. Always consult a licensed clinician before considering any GLP-1 therapy. See our Affiliate Disclosure.
How retatrutide was dosed in trials
Retatrutide is a once-weekly injectable triple agonist (GLP-1, GIP and glucagon receptors) developed by Eli Lilly. In the phase-2 trial published in the New England Journal of Medicine (2023), participants didn’t start at their target dose. They began at a low amount and stepped up every four weeks — a process called titration — to let the body adjust and keep nausea manageable.
Because the drug is still in development, there is no official patient dosing label. Every figure on this page comes from that published trial and is provided so you can understand what people mean by “retatrutide dosing.”
Retatrutide dose escalation chart (trial-reported)
In the trial, doses rose in 4-week steps. Someone assigned to the 12 mg target didn’t jump straight there — they climbed a ladder from 2 mg upward. This is the escalation pattern the study used for the higher-dose groups:
| Weeks | Weekly dose (12 mg target group) | Purpose |
|---|---|---|
| 1–4 | 2 mg | Initiation — assess tolerance |
| 5–8 | 4 mg | First step-up |
| 9–12 | 6 mg | Continued titration |
| 13–16 | 8 mg | Approaching target |
| 17+ | 12 mg | Maintenance (target) |
Lower-target groups (1, 4 and 8 mg) followed shorter versions of the same ladder and simply stopped climbing once they reached their assigned dose. Exact schedules were set and supervised by clinicians in a controlled study.
Weight loss by dose in the study
Higher target doses produced more weight loss at 48 weeks in the phase-2 trial — the clearest reason people ask about the 8 mg and 12 mg amounts specifically:
| Target dose | Approx. mean weight reduction (48 weeks) |
|---|---|
| 1 mg | ~8–9% |
| 4 mg | ~17% |
| 8 mg | ~17–18% |
| 12 mg | ~24% |
The trade-off: the same higher doses that drove more weight loss also drove more gastrointestinal side effects. Slow titration is how the study kept the higher doses tolerable. See our retatrutide side effects breakdown for the safety data.
Why titrate instead of starting high?
Because side effects — not results — are what usually make people quit a GLP-1. Nausea, reduced appetite and digestive discomfort are strongest right after a dose increase. Stepping up every four weeks gives the body time to adapt at each level, which generally makes the whole course more tolerable than jumping straight to a high dose.
Retatrutide reconstitution: how much BAC water?
“How much bacteriostatic water for 10 mg retatrutide?” is one of the most searched questions on this topic. Reconstitution is simply mixing a freeze-dried (lyophilized) peptide with bacteriostatic water so a known volume contains a known amount. The water you add changes the concentration, not the total in the vial:
| Vial | BAC water added | Concentration | Per 0.1 ml (10 units) |
|---|---|---|---|
| 10 mg | 1 ml | 10 mg/ml | 1 mg |
| 10 mg | 2 ml | 5 mg/ml | 0.5 mg |
| 5 mg | 1 ml | 5 mg/ml | 0.5 mg |
Adding more water doesn’t reduce the total peptide — it just spreads it across more liquid, changing how many units equal a given amount. For a hands-on version, use our retatrutide dosage calculator. This is explanatory only, not a directive to prepare or use anything.
Want a GLP-1 you can actually get prescribed?
Retatrutide isn’t available by prescription yet. If you want a legal, clinician-supervised option today — like semaglutide or tirzepatide — compare the top vetted online providers.
Retatrutide dosage: frequently asked questions
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