Retatrutide Is Getting Closer to the FDA: Could This Be the Next Big Weight Loss Drug? Indeed, retatrutide has been presented as a potential successor to Wegovy and Zepbound in recent years.
However, these projections may need updating: Eli Lilly has recently reported positive results from phase III trials, including a more than 25% average decrease in initial weight among non-diabetic adults who received the highest dose. According to the company’s press release, they aim to submit retatrutide for FDA approval in the first quarter of 2027.
This would enable the medication to enter the market. However, retatrutide is not currently authorized for human administration in any jurisdiction. This is an essential distinction since rogue manufacturers have already begun selling unapproved “retatrutide.”
Why Retatrutide Is Different
While Wegovy’s active ingredient, semaglutide, and Zepbound’s tirzepatide, both target the glucagon-like peptide 1 (GLP-1) receptor, retatrutide also acts on the GIP receptor and a hormone called glucagon. The latter mechanism appears to be the most promising because glucagon can both raise blood sugar levels and promote energy expenditure. In turn, this means that drugs that simultaneously affect GIP, GLP-1, and glucagon may substantially suppress appetite while also increasing calorie expenditure.
It is not yet established whether the impact of each receptor is equal. Nevertheless, the combined influence has demonstrated extraordinary efficacy in clinical trials.
The Phase III Results Are Impressive
As mentioned, Lilly announced encouraging results from TRIUMPH-1 in May 2026. This trial involved obese or overweight individuals with at least one metabolic abnormality (but no diabetes), who had been given either 4 mg, 9 mg, or 12 mg of retatrutide or a placebo. After 80 weeks, the average reduction in body weight was between:
• 19.0% (4 mg), 25.9% (9 mg), 28.3% (12 mg)
while the average reduction was only 2.2% in the placebo group. It is worth noting that the average study participant weighed 249 pounds at the beginning of the trial. Thus, an individual who has received a 12 mg dose would have lost 70 pounds on average. Additionally, nearly 50% of patients in this group reduced their initial weight by at least 30%.
Furthermore, a subgroup analysis of patients with a BMI of at least 35 revealed that, on average, individuals who received 12 mg lost 30.3% of their weight over a course of 104 weeks. This implies that some of them may have continued to lose weight even after 80 weeks.
These figures, however, conceal a critical detail: the numbers quoted pertained to the “efficacy estimand,” a term that reflects the influence of the drug while the patients continued to receive regular doses of retatrutide. When researchers began to consider patients who dropped out of the trial, the results were significantly more modest, although they still remained astonishing: 17.6%, 23.7%, and 25.0% for the three doses.
It is hard to say which of these figures is more meaningful: in essence, the first study estimates efficacy if treatment is fully compliant, while the second reflects the real-world scenario when some patients discontinue the medication.
Nevertheless, the results published by Lilly in TRIUMPH-1 – which have yet to undergo peer-review – will undoubtedly pique the interest of many medical professionals. The most critical question, however, is how effective retatrutide would be in patients with diabetes.
Weight Loss Medication for People with Diabetes: Lower, But Still Substantial
It is well-established that weight loss pharmaceuticals are usually less effective in diabetic individuals than in non-diabetic ones. Retatrutide was no exception, though the difference between the two groups was far smaller than previously observed with other drugs.
Indeed, in TRIUMPH-2, which included individuals with obesity or overweight and type 2 diabetes, the average reduction in body weight was as high as 20.8% after 80 weeks. Furthermore, the drug decreased A1C levels by as much as 1.6 percentage points on average.
TRIUMPH-3, which involved people with extreme obesity and secondary cardiovascular disease, with or without diabetes, also yielded outstanding results: the average decline in body weight was 22.6% at the highest dose.
These results convinced Lilly that retatrutide can be a viable addition to the U.S. market in the early 2020s. The company also plans to study the medication’s effects on sleep apnea, osteoarthritis, non-alcoholic fatty liver disease, and cardiovascular and renal outcomes.
Can It Compete With Zepbound?
Possibly, but it is too soon to tell. While Zepbound has not yet demonstrated such excellent results in clinical trials, it has the advantage of being FDA-approved and commercially available. Moreover, tirzepatide has an extensive clinical literature base, including a large number of trials investigating its safety and efficiency profiles.
On the other hand, Lilly’s phase III trial results for retatrutide were extraordinarily impressive, particularly among non-diabetic individuals. Nevertheless, it is hard to compare the efficacy of different medications based on results from distinct trials, since they rarely involve identical patient groups and follow-up periods.
Lilly has initiated a trial comparing the effects of retatrutide and tirzepatide in people with obesity, which should help establish whether the new medication can indeed compete with Zepbound. However, this study is likely to conclude after the initial FDA application has been reviewed.
Even if the average weight loss differs significantly between tirzepatide and retatrutide, it is essential to keep in mind that “more” is not always “better,” at least for individual patients. Someone who has successfully reduced their weight on a lower dose of an approved medication may find that the advantages of switching to an investigational drug, which generally involves greater risks, are minimal.
Adverse Effects Are Worth Considering as Well
The most common side effects of retatrutide are similar to those of other GLP-1 receptor agonists: nausea, diarrhea, constipation, vomiting, and decreased appetite. In TRIUMPH-1, for instance, 42.4% of the 12 mg group and 25.3% of the 9 mg group experienced nausea, compared to just 4.8% in the control group. Vomiting was also a prevalent adverse effect, with 25.3% and 13.3% of the high- and medium-dose groups, respectively, reporting this side effect.
The frequency and severity of gastrointestinal problems increased with the dosage. Furthermore, researchers also observed dysesthesia (unusual sensations, including numbness, tingling, burning, or pain on the skin) in 12.5% of the 12 mg group and 4.3% of the 9 mg group, compared to less than 1% in the control group.
Apart from the standard adverse effects associated with GLP-1 medications, rapid and substantial weight loss can also lead to a number of undesirable consequences. For example, considerable loss of muscle mass – in addition to fat – can occur if calorie intake and protein intake are inadequate.
Gallbladder disease, dehydration, and electrolyte imbalance are also possible complications that should be considered when discontinuing the medication. All of these factors must be taken into account by the FDA when determining whether retatrutide will receive approval and what restrictions, if any, will be imposed.
When Can Patients Expect Retatrutide?
As previously mentioned, Lilly expects to submit its application for FDA approval in early 2027. The FDA will then need to accept and review this application.
Therefore, it is unlikely that retatrutide will become a regular prescription medication before the second half of 2027, and it may take considerably longer for it to be approved. Additionally, the timeline may depend on the FDA’s inquiries and whether additional research is required.
Before FDA approval, a physician cannot legally prescribe retatrutide, and a pharmacy cannot prepare a compounded equivalent. This is not the same as obtaining an investigational drug from a compounding pharmacy for a specific medical need when a prescription medication is unavailable.
Social media, bodybuilding forums, wellness clinics, and other outlets sell “research retatrutide” – in many cases, this product has nothing to do with the medication developed by Lilly. The powder may contain an incorrect dose of the active substance, various impurities, or even an entirely different compound. According to the company’s press release published in August 2026, Lilly has already filed a lawsuit against several U.S.-based firms that sell counterfeit retatrutide.
Patients may find it difficult to wait for the drug to receive approval. However, receiving doses of an unapproved substance is simply too dangerous.
Retatrutide has a genuine chance of becoming the next “blockbuster” obesity medication. The phase III results are nothing short of extraordinary, and Lilly is prepared to bring this drug to the attention of the FDA. Nevertheless, the most crucial characteristic of retatrutide – for now – remains “investigational.” For now, this medication is an exciting prospect that is worth waiting for.
