Retatrutide
Retatrutide (also known as LY3437943) is an experimental weight-loss and diabetes medication developed by Eli Lilly
It’s a triple agonist that activates three different hormone receptors involved in metabolism:
GLP-1 (glucagon-like peptide-1) → improves insulin secretion, slows gastric emptying, reduces appetite.
GIP (glucose-dependent insulinotropic polypeptide) → enhances insulin secretion and may have synergistic effects with GLP-1.Glucagon receptor → increases energy expenditure and fat burning.
Clinical Data (as of 2025)
In phase 2 trials (published 2023, NEJM), participants with obesity (without diabetes) lost up to 24% of their body weight in 48 weeks at the highest dose (12 mg weekly).
People with type 2 diabetes saw improvements in both weight and HbA1c (blood sugar control).Common side effects: nausea, vomiting, diarrhea, constipation—similar to other incretin-based therapies (like semaglutide and tirzepatide).It is considered one of the most promising next-generation obesity/diabetes drugs, potentially even more effective than tirzepatide (Mounjaro/Zepbound).
Status
Currently in phase 3 clinical trials.
Not yet FDA-approved (as of August 2025).Good question. Right now, retatrutide is not approved for bodybuilding or athletic use, and its effects in that setting haven’t been studied. But here’s what’s relevant if bodybuilders are looking at it:
🔹 Potential Effects for Bodybuilders
Retatrutide produces very large reductions in body fat (comparable or greater than tirzepatide/semaglutide).Could help reach extreme leanness with less reliance on harsh cutting methods.
Muscle Mass Concerns
Rapid weight loss often leads to loss of lean mass, not just fat.Early trial data suggest that some lean mass is lost alongside fat with incretin-based drugs.This means without careful nutrition and resistance training, retatrutide could reduce muscle size and strength.Appetite Suppression
Strongly suppresses appetite, which can help with cutting phases.But for bulking or maintaining high caloric intake, this is a disadvantage.Energy & Training Performance
Lower energy intake and slowed gastric emptying can reduce gym performance.Some users on GLP-1 drugs report fatigue during intense training.
🔹 Risks & Unknowns
Unstudied in athletes → No clinical data on effects during intense resistance training.
Possible muscle loss → Could compromise physique goals if not carefully managed.Side effects → Nausea, GI upset, dehydration risk.Not legal for competition → Likely banned by WADA, since GLP-1 agonists are performance-altering and not medically indicated in healthy athletes.Long-term safety in non-obese, non-diabetic populations is unknown.
Retatrutide may eventually become the most powerful fat-loss drug available, but in bodybuilding it’s a double-edged sword: great for cutting fat, risky for preserving muscle.