What it is
Retatrutide is a triple GLP-1/GIP/glucagon receptor agonist — meaning it targets three separate hormone receptor systems at once. In Phase 2 trial data it produced up to a 24% reduction in body weight. It is categorized under weight loss in the PeptidesAI encyclopedia. It is an investigational drug: it has not completed the FDA approval process and is not approved for human use outside of clinical trials.
How it's thought to work
Retatrutide activates three receptor systems simultaneously. The GLP-1 receptor is associated with appetite suppression and slowed gastric emptying. The GIP receptor is associated with insulin signaling and fat metabolism. The glucagon receptor is associated with increased energy expenditure and fat oxidation. Activating all three receptor systems at once, rather than one or two, is the proposed explanation for the size of the weight-loss effect seen in trials.
What the research says
A Phase 2 trial by Jastreboff and colleagues, published in the New England Journal of Medicine in 2023, reported body weight reduction of up to 24.2% at 48 weeks. A substudy of the same trial in participants with MASLD (metabolic dysfunction-associated steatotic liver disease) reported reductions in liver fat of up to 86%. Retatrutide has not been approved and remains an investigational compound studied in clinical trials.
Reported side effects
The most commonly reported side effect is nausea, along with diarrhea, vomiting, constipation, and decreased appetite. These are generally described as mild to moderate.
Reconstitution
Retatrutide is supplied as a lyophilized (freeze-dried) powder and is typically reconstituted with bacteriostatic (BAC) water before use, with standard guidance to swirl gently rather than shake. It commonly comes in 5 mg and 10 mg vials, and reconstitution follows the same dilution math regardless of which of those two sizes is on hand.
Worked example. A 5 mg vial is 5,000 mcg. Reconstituted with 1 mL of BAC water, that works out to 5,000 mcg ÷ 1 mL = 5,000 mcg/mL. On a U-100 insulin syringe, where each unit is 0.01 mL, that means each unit holds 5,000 × 0.01 = 50 mcg. A 10 mg vial reconstituted with 2 mL of BAC water comes out to the same concentration — 10,000 mcg ÷ 2 mL = 5,000 mcg/mL, so again 50 mcg per unit — because the ratio of peptide to water is unchanged. Use the peptide reconstitution calculator to work out the concentration and units for any vial size and water volume.
Important notes
Retatrutide is an investigational compound and is not FDA-approved. Outside of clinical trials, it is sold only by unregulated research-chemical suppliers.
Frequently asked questions
These questions cover the same ground as the sections above, in a shorter format.
What is retatrutide?
A triple GLP-1/GIP/glucagon receptor agonist — an investigational drug studied for weight loss. It is not approved by the FDA and remains in clinical trials.
How is retatrutide thought to work?
It activates the GLP-1, GIP and glucagon receptors at once, which are associated respectively with appetite suppression and slowed gastric emptying, insulin signaling and fat metabolism, and increased energy expenditure and fat oxidation.
What does the retatrutide trial data show?
A Phase 2 trial (Jastreboff et al., NEJM 2023) reported up to 24.2% body weight reduction at 48 weeks. A substudy of the same trial in participants with MASLD reported reductions in liver fat of up to 86%. It remains investigational and is not FDA-approved.
What are the reported side effects?
Nausea is the most commonly reported effect, along with diarrhea, vomiting, constipation, and decreased appetite — generally mild to moderate.
How many mcg is one unit from a 5 mg retatrutide vial?
With 1 mL of BAC water, a 5 mg vial is 5,000 mcg/mL, so one unit on a U-100 syringe (0.01 mL) holds 50 mcg.
The full entry, plus the calculator
The PeptidesAI app has the complete encyclopedia entry for retatrutide — one of 70 compounds covered — including protocol notes, plus the reconstitution calculator, a dose log and reminders. Free to download on iPhone.
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