Although retatrutide is very effective for weight loss, it has side effects that could affect certain people such as faster heart beats, and heart complications.
Dr Mariella Borg Buontempo
Retatrutide produced average weight loss of 28.3% over 80 weeks in its largest trial so far, and it raises heart rate. Trials have not shown that it causes serious heart complications; serious adverse events were about as common as on a placebo. The drug is still experimental.How we reached this verdict ↓
Analysis and evaluation
Retatrutide produces some of the largest weight losses seen with any drug, and it raises heart rate. Trials so far have not shown it causes heart complications.
Very large weight loss
Retatrutide is an experimental drug that acts on three gut-hormone receptors. In its Phase 2 trial, people on the highest dose lost around 24% of their body weight on average after 48 weeks. In TRIUMPH-1, the first large Phase 3 trial, reported by Eli Lilly in May 2026, average weight loss reached 28.3% at 80 weeks.
Side effects were common. In TRIUMPH-1, 11.3% of patients stopped treatment because of them, and 12.5% reported dysesthesia, an abnormal sensation in the skin.
A higher heart rate is documented
In the Phase 2 trial, heart rate rose on retatrutide. The increase was larger at higher doses, peaked during treatment and then declined. Whether that matters for a given patient depends on their health and history, which fits the speaker's "certain people".
Heart complications are not shown
Heart rhythm problems were reported in the Phase 2 trial, but most were mild or moderate, and serious adverse events overall were about as common on retatrutide as on a placebo. Its longer-term effect on the heart is the subject of a dedicated cardiovascular outcomes trial in the TRIUMPH programme, which has not yet reported.
Evaluation
What was said is partly right. Retatrutide is very effective for weight loss and it raises heart rate. The step to heart complications goes beyond the evidence: trials have recorded some heart-related events, but have not shown that the drug causes them. Its wider cardiovascular safety is still being tested.
Editorial note
How we assessed this claim
We split the claim into the effect it describes and the harm it attaches to that effect: whether retatrutide works for weight loss, whether it raises heart rate, and whether trials show it causes heart complications. We relied on published trial results and the manufacturer's Phase 3 announcements.
The established part holds: the weight loss is large and the higher heart rate is documented. The harm attached to it, heart complications, is not shown by the trials so far, which keeps the claim below True but lacks context. The speaker framed the risk with "could" and "certain people", which keeps it above Misleading. That lands it at Not entirely accurate, the same reasoning used for the muscle and bone claim in this episode.
Limitations
- Retatrutide has not completed the approval process. Its safety profile can change as larger and longer trials report, including a dedicated cardiovascular outcomes trial.
- The TRIUMPH-1 figures come from the manufacturer's announcement; the full peer-reviewed paper was not yet available to us.
- A side effect recorded in a trial is not proof that the drug caused every event. Researchers compare rates between drug and placebo groups before drawing conclusions.
Sources
- Jastreboff A.M. et al., Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial, New England Journal of Medicine (2023)
- Eli Lilly and Company, Lilly's triple agonist retatrutide delivered powerful weight loss (TRIUMPH-1 results, May 2026)
- ClinicalTrials.gov, TRIUMPH programme for retatrutide, including the cardiovascular outcomes study