Retatrutide weight loss plateau hopes outpace the Phase 3 evidence

A GP's newspaper column has put the retatrutide weight loss plateau question in front of a wide UK audience. Writing in the Daily Mail on 1 November, Dr Saira Bano said she would move many patients who stall on Mounjaro to Eli Lilly's experimental triple agonist once it is approved. Retatrutide is still a Phase 3 molecule, and nothing on our board moves today. This explainer sets her case against what Lilly has reported from its TRIUMPH program, the side effect signal, the filing timeline and the risk from illegal copies.

A GP column bets on retatrutide for the Mounjaro plateau

Bano writes that she works as a GP in both the NHS and private practice, specialising in obesity, and that she has treated about 20,000 patients with weight loss injections over three years. In her Daily Mail column she describes a recurring group: mostly women aged 35 to 60 who have taken the top dose of Mounjaro for a year or more, lost a lot of weight, then stopped losing while still living with obesity. She calls this the GLP 1 plateau, and the headline calls it the Mounjaro plateau. Her case is about mechanism. Wegovy acts on the GLP-1 receptor, Mounjaro adds GIP, and retatrutide adds a third target, glucagon, which she says may raise the energy the body burns as well as cut how much people eat.

Two parts of the column are forecasts, not findings. Bano says she expects retatrutide to arrive towards the end of next year, and that she will then give it to many of her patients. No regulator has set that date. Her retatrutide weight loss plateau argument is also a hypothesis: the glucagon effect on energy use is a proposed mechanism, and the column offers no data on people who switched after stalling on tirzepatide, the molecule sold as Mounjaro. She does add limits. People with only a few pounds to lose should not use it, she writes, and diet and exercise still decide whether results last. That caution is the part of the column best backed by current evidence, while the rest depends on trials that asked a different question.

What the TRIUMPH 1 trial showed

The headline number in the column comes from the TRIUMPH-1 trial, a Phase 3, 80 week, randomized, double blind study registered as NCT05929066. It enrolled 2,339 adults with obesity, or overweight plus at least one weight related health problem, who did not have type 2 diabetes. Lilly's topline figures, as summarised by the Drugs.com reference page, show that all three doses met the primary and key secondary endpoints. On the highest dose, participants lost an average of 28.3 percent of their body weight at 80 weeks, against 2.2 percent on placebo. The lowest dose gave 19.0 percent, and 45.3 percent of people on the top dose lost at least 30 percent. These are efficacy estimand results, which Lilly defines as the effect had every randomized person stayed on the study drug.

On the highest dose, participants lost an average of 28.3 percent of their body weight at 80 weeks, against 2.2 percent on placebo.

Bano compares that with about 15 percent for Wegovy and 20 percent for Mounjaro. Those come from separate trials with different people, doses and lengths, so they are a rough guide, not a ranking. The bigger gap for the retatrutide weight loss plateau argument is design. TRIUMPH-1 compared retatrutide with placebo in people starting treatment, and its reported results do not describe people who had already stalled on tirzepatide. The two companion trials Lilly reported on 23 July gave smaller average losses in harder to treat groups, as the table shows. In diabetes, Lilly has also tested the drug in a Phase 3 trial against Ozempic, which is a head to head result but still not a switch study. A switch trial is the evidence the plateau claim needs.

Retatrutide side effects rise with dose

Tolerability is where the column is most careful. Bano writes that a quarter of people on the highest dose vomited, more than four in ten had nausea, and one in nine stopped because of side effects. The Drugs.com summary of TRIUMPH-1 puts nausea at 42.4 percent on the highest dose against 28.6 percent on the lowest, and stopping for adverse events at 11.3 percent on the top dose against 4.9 percent on placebo. Dysesthesia, an unusual skin sensation such as tingling or burning, was reported in 12.5 percent on the top dose against 0.9 percent on placebo. Lilly has said the side effects were generally mild to moderate and that most resolved during treatment. Even so, the pattern is clear: the higher the dose, the more people struggle to stay on it.

The same pattern appears beyond TRIUMPH-1. In TRIUMPH-2, Lilly reported nausea in 28.0 percent on the top dose against 8.0 percent on placebo, and vomiting in 15.7 percent against 4.2 percent. Our earlier report on retatrutide side effects in TRANSCEND found more people stopping the higher dose than stopping Ozempic. For a patient who already feels sick on Mounjaro, a stronger drug may be harder, not easier, to tolerate, and Bano says she already sees patients vomiting on current injections. Response and side effects also differ from person to person, and a recent GLP1R variant study found genes explain only a small part of that spread. Who gains most from a third hormone target remains an open question.

Retatrutide FDA submission and counterfeit pens

On 23 July 2026 Lilly said it plans to submit a Biologics License Application to the FDA in the first quarter of 2027. Kenneth Custer, who leads Lilly Cardiometabolic Health, said the newest results gave the company "the clinical data package to support global submissions" for obesity, knee osteoarthritis pain and obstructive sleep apnea. That makes the retatrutide FDA submission the next fixed checkpoint. The release we read gives no UK filing date, and an FDA review typically takes many months after a file is accepted. Bano's end of next year estimate is therefore a plausible reading of the timeline, not a confirmed date. Until a regulator rules, retatrutide stays at Phase 3 on our board. Lilly describes it as an investigational, first in class GIP, GLP-1 and glucagon triple hormone receptor agonist.

The column also warns about illegal supply. Bano writes that retatrutide is not approved anywhere, that factories in Britain making fake injection pens have been raided, and that one NHS patient who believed they were taking it had in fact been injecting insulin. We could not independently check the raids, so we report them as her account. Lilly states that retatrutide is an investigational molecule that "cannot be legally sold or marketed for human use." That means any counterfeit retatrutide pen or vial has no regulator checking its contents, strength or sterility, and the insulin case shows how badly that can go. Today the only legitimate access is through a registered clinical trial. Anyone stalled on a licensed drug should raise it with the prescriber who manages their treatment.

Conclusion

Bano's column is a clinician's bet, not a new data point. The retatrutide weight loss plateau idea rests on a plausible mechanism and large gains against placebo, but the reported trials did not test people who stalled on tirzepatide, and side effects climb with dose. Lilly's planned US filing in early 2027 is the next fixed date. Until a regulator decides, retatrutide is unapproved everywhere and anything sold under its name sits outside the law. This is research reporting, not medical advice.