GLP-1 / fat loss
Retatrutide Side Effects: The 6 I Actually Felt
A first-person rundown of what retatrutide actually feels like, and how the side effects track your dose.
The quick version
- What it is: a triple-agonist GLP-1, the strongest weight-loss peptide in trials.
- Result: about 24 percent of body weight lost at 48 weeks on the top dose.
- Catch: stomach side effects that track your dose, so titrate slowly.
What it is
Retatrutide is an injectable peptide that hits three receptors at once: GLP-1, GIP, and glucagon. People call it a triple agonist. It is still experimental. No drug agency has approved it, and the large phase 3 trials are still running.
What the research shows
The headline number comes from a phase 2 trial in the New England Journal of Medicine. At the top dose of 12 mg per week, people lost about 24 percent of their body weight over 48 weeks (Jastreboff et al., 2023). That is the strongest weight result reported for any single drug so far. In the same trial the common side effects were all stomach related: nausea, diarrhea, constipation, and vomiting. They were worse at higher doses and during each dose increase.
What it felt like
I ran reta for a cut, not a medical reason. What I felt, roughly in order: nausea for a day or two after a dose bump, early fullness so meals got small, some constipation, a few nights of lighter sleep, and a flat week of energy at the start of each new dose. Nothing put me near a doctor, but greasy food made the nausea worse every time.
Dosing reality
The trial started people at 2 mg or 4 mg and climbed slowly. I started lower, at 1 mg per week, and only moved up every 4 weeks. Going slow is the biggest lever on how rough this feels. Reta is a research compound, so there is no approved label dose to copy.
The one mistake to avoid
The mistake I see most is jumping the dose because the scale stalls for a week. The stall almost always breaks on its own. Climbing faster mostly buys more nausea, not more fat loss.
Bottom line
Reta works, but the side effects track your dose and how fast you climb. Start low, hold each step, and most of them stay manageable.
Reminder: I am not a doctor and this is not medical advice. It is my own notes and reading of the research. Peptides sit in a legal grey area, research-grade is a real category, and it is on you to verify your own compliance. Talk to a qualified professional before you start anything, especially if you take other medication.