What Phase 1 and Phase 2 trials administered — the retatrutide dosage record.

Before reading this page

Retatrutide is an investigational drug. It is not approved, not commercially available, and has no labeled dosage from any regulatory authority. This page documents what doses were studied in published clinical trials and what the pharmacokinetics look like. It is a reading of published study-design facts.

The doses described here were administered to clinical trial participants under physician monitoring, with regular safety assessments, laboratory testing, and the ability to de-escalate or discontinue. They were not self-administered, unmonitored, or sourced from unregulated suppliers. The context matters: the same number on a vial of unverified material in an unmonitored setting is not the same as a clinical-trial protocol. This page does not recommend, advise, or instruct on retatrutide use of any kind.

For Retatrutide research on the clinical outcomes at these doses, see the research page.

Retatrutide dosage: what the trials studied

Across the published Phase 1b and Phase 2 trial programs, retatrutide was studied exclusively as a once-weekly subcutaneous (injected into the fatty layer beneath the skin) formulation. The dose range explored was 0.5 mg to 12 mg.

Phase 1b (first-in-human, 72 adults with type 2 diabetes, 12 weeks): Five escalating dose cohorts — 0.5, 1.5, 3, 3/6, and 3/6/9/12 mg once weekly. The highest-dose cohort stepped through 3, 6, 9, and 12 mg over the 12 weeks of the study ^[4].

Phase 2 obesity trial (338 adults with obesity, 48 weeks): Fixed doses of 1, 4, 8, or 12 mg once weekly with dose escalation. The escalation schedule used lower starting doses and gradual up-titration (dose escalation — gradually increasing the dose over weeks to manage tolerability, particularly of GI side effects) to reach the target dose ^[1].

Phase 2 type 2 diabetes trial (281 adults, 36 weeks): Dose-escalating regimens from 0.5 mg up to 12 mg once weekly. Stepwise escalation was used to manage GI tolerability ^[2].

Phase 2a MASLD substudy (98 adults, 48 weeks): 1, 4, 8, and 12 mg once weekly, matching the obesity-trial arms ^[5].

Retatrutide half life

The Phase 1b study established a half-life of approximately 6 days for retatrutide in humans ^[4]. Half-life — the time for the blood concentration of a drug to fall by half — determines how often it needs to be administered. A 6-day half-life is sufficient to maintain pharmacologically active plasma levels across a 7-day (once-weekly) dosing interval, which is why all Phase 2 trials used once-weekly administration.

The extended half-life derives from the C20 fatty-diacid acylation on the peptide backbone. This modification enables retatrutide to bind albumin (the major protein in blood plasma) non-covalently — slowing its clearance from circulation. The same albumin-binding strategy is used to extend the half-life of other GLP-1-class agents.

At steady state (reached after approximately 4-5 half-lives, or roughly 3-4 weeks of once-weekly dosing), plasma concentrations are approximately 4-5 times higher than after the first dose. This is why trial protocols use dose-escalation schedules that start at a lower amount and step up over weeks — the combination of increasing dose and accumulating plasma concentration is managed together to limit GI adverse effects during the ramp-up period.

Retatrutide side effects: the dose-response pattern

The dominant safety signal in all Phase 2 trials was dose-dependent GI adverse events. Nausea, diarrhea, vomiting, and constipation were the most commonly reported adverse events and the principal reason for discontinuation — 18% discontinuation at the highest dose in the obesity trial ^[1].

GI effects arise mechanistically from GLP-1-receptor-mediated slowing of gastric emptying and altered GI motility. The slowed gastric transit (food stays in the stomach longer before moving to the small intestine) is the mechanism underlying both early satiety and nausea. At higher doses, the effect on gastric motility is more pronounced.

The dose-dependent heart-rate increase is the second key safety signal: mean increases of approximately 5-7 bpm at the highest doses, peaking around 24 weeks ^[1]. The GCGR (glucagon receptor) arm drives cardiac chronotropy (heart-rate increase) via cAMP/PKA signaling — a known glucagon receptor pharmacology effect.

In the type 2 diabetes trial, participants on background insulin required dose de-escalation of their insulin during the study, reflecting the combined insulin-augmenting effects of GLP-1 and GIP agonism ^[2].

Retatrutide cost

Retatrutide has no commercially available price — it is not approved and not sold as a prescription drug. No manufacturer's suggested retail price (MSRP), insurance pricing, or formulary coverage exists for retatrutide as an approved pharmaceutical product.

For context: investigational drugs in Phase 3 trials are typically not commercially available at any price outside of trial enrollment. The FDA's Expanded Access program provides a pathway for some patients to access investigational drugs outside trials under specific conditions, but no approved expanded access program for retatrutide has been publicly announced.

The gray market for research-labeled retatrutide exists, but pricing in that market does not reflect pharmaceutical pricing; it reflects unregulated research chemical supply chains. This site does not source, link, or reference vendors in that market.

How to reconstitute retatrutide

Retatrutide does not have an approved pharmaceutical formulation. There is no FDA-approved or manufacturer-issued reconstitution protocol for retatrutide outside of a clinical trial.

In the published Phase 1b and Phase 2 trials, retatrutide was administered as a clinical investigational product in a pre-filled pen injector system — not as a lyophilized (freeze-dried) powder requiring reconstitution. The solvent composition, concentration, and excipients of the clinical-trial formulation are specified in the respective study protocols and the published methods sections, not in public labeling.

Any reconstitution protocol circulating online for research-labeled retatrutide vials is not derived from an approved pharmaceutical standard. This site does not provide reconstitution instructions — to do so would be to offer preparation guidance for an unverified, unapproved substance with no verified identity or purity.

Retatrutide availability: why the pharmacy framing matters

This domain name includes the word pharmacy. To be explicit about what that means and does not mean: retatrutide is not available at a pharmacy. It is not available via a pharmacist, a compound pharmacy (503A or 503B), or a telehealth prescriber. It is an investigational new drug in Phase 3 trials. Pharmacies cannot legally dispense it.

The FDA took specific action in 2025 against compounding pharmacies and research chemical vendors marketing retatrutide — issuing warning letters citing violations of the Federal FD&C Act, because retatrutide's clinical development status makes it ineligible for 503A/503B compounding or research-chemical sale under current FDA policy.

This site is an independent research digest. The domain name signals the intent to rank for availability-related queries and provide accurate information about retatrutide's actual availability status. No pharmacy services, prescription services, or pharmaceutical products are offered here.