Retatrutide (also called LY3437943) is an investigational once-weekly injectable medicine being studied for obesity and related metabolic conditions. It’s often described as a “triple agonist” because it activates three hormone receptors involved in appetite, glucose regulation, and energy balance: GIP, GLP‑1, and glucagon receptors.

Because retatrutide is still under study, there is no FDA‑approved dose and no official “prescribing information” for routine care. What we do have publicly is the dosing structure used in major clinical trials: which weekly dose levels were tested, how participants were moved up to higher doses (“titration”), and why.

Important: This is educational information, not medical advice and not instructions for use. Clinical-trial dosing happens under controlled conditions with screening, monitoring, and rules for pausing or stopping treatment.

Short answer

In the best-known Phase 2 obesity trial (ClinicalTrials.gov NCT04881760), retatrutide was given once weekly for 48 weeks, with multiple study arms testing different target weekly dose levels (including 1 mg, 4 mg, 8 mg, and 12 mg).
For arms targeting 4 mg or higher, participants typically started at a lower weekly dose and then increased gradually (“titrated”) over the first weeks.
The point of titration was to reduce side effects, especially gastrointestinal symptoms, and to improve the odds participants could stay on treatment long enough to evaluate outcomes.
The FDA has explicitly warned about unapproved and fraudulent GLP‑1-related products and states that retatrutide cannot be used in compounding under federal law.

Why dosing schedules matter more than the headline “mg” number

A trial dose is better understood as a dosing strategy that includes:

starting dose
target dose
titration pace
monitoring schedule
safety/stopping rules
eligibility and exclusion criteria

These elements work together. That’s also why you can’t safely “copy” a trial schedule outside a trial.

The Phase 2 obesity trial dosing structure (NCT04881760)

The landmark Phase 2 trial in adults with obesity/overweight is registered as NCT04881760 and published in NEJM (PubMed summary). Public sources describe placebo and multiple once‑weekly retatrutide regimens, including target doses 1 mg, 4 mg, 8 mg, and 12 mg, with step-up (titration) used for higher target doses.

A key reported point: GI adverse events were common and partially mitigated by a lower starting dose.

Why titration is used (tolerability and safety)

With incretin-based therapies, the most common side effects are GI (nausea, vomiting, diarrhea, constipation). When dose increases happen too fast, side effects can become severe (and dehydration can become dangerous). Titration is a practical way to make therapy more tolerable while maintaining safety monitoring.

Why trial titration can’t be copied as “DIY dosing”

Even if someone could obtain a product claiming to be retatrutide, trial dosing is inseparable from:

protocol-driven monitoring
standardized product quality + cold chain
structured adverse-event reporting
investigator judgment and stopping rules

And in the US, retatrutide remains investigational and is not legally marketed as an FDA‑approved drug.

References

ClinicalTrials.gov (API) NCT04881760: https://clinicaltrials.gov/api/v2/studies/NCT04881760
PubMed (NEJM Phase 2 obesity trial): https://pubmed.ncbi.nlm.nih.gov/37366315/
PMC substudy (dose escalation discussion): https://pmc.ncbi.nlm.nih.gov/articles/PMC11271400/
FDA (unapproved GLP-1 drugs; retatrutide compounding prohibition): https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers/fdas-concerns-unapproved-glp-1-drugs-used-weight-loss