Retatrutide explained: the triple-hormone shot breaking weight-loss records

You may have seen the headlines: an experimental injection helped people lose close to a third of their body weight. That drug is retatrutide, made by Eli Lilly, the company behind Zepbound and Mounjaro. It is not approved yet, but its trial results have changed what doctors think a medicine can do for weight.

Why "triple"?

Your gut and pancreas release hormones after you eat that tell your body how hungry to feel and how to handle energy. Weight-loss medicines copy these hormones.

Semaglutide (Wegovy) copies one of them, GLP-1, which reduces appetite and makes you feel full sooner. Tirzepatide (Zepbound) copies two, GLP-1 and GIP, which seems to boost the effect and ease some stomach side effects. Retatrutide adds a third: glucagon. Glucagon normally tells the body to release stored energy, and in this combination it appears to increase the energy the body burns and help clear fat from the liver. So retatrutide works on both sides of the equation: you eat less, and your body may burn a little more.

What the trials found

The biggest trial, TRIUMPH-1, included 2,339 adults with obesity or overweight but without diabetes. After 80 weeks (about 18 months), people on the top 12 mg weekly dose lost 28.3% of their body weight on average, among those who kept taking it. Counting everyone who started, including people who stopped, the figure was 25.0%. People on placebo lost about 2%.

For someone who starts at 110 kg, 28% is about 31 kg. In a longer extension for people with a higher starting weight, the top-dose group kept losing and averaged about 30% after two years.

Two more trials reported in July 2026. In people with type 2 diabetes (TRIUMPH-2), the top dose produced 20.8% weight loss; people with diabetes usually lose less on these medicines. In people with severe obesity and heart disease (TRIUMPH-3), weight loss reached 22.6%. That trial did not show a clear reduction in heart attacks and strokes; the result was inconclusive rather than negative.

The side effects

Like other medicines in this family, retatrutide mostly causes stomach side effects while the dose is being raised. On the top dose, 42% of people reported nausea at some point.

Retatrutide also has a less familiar one: dysesthesia, an unusual skin sensation such as tingling, burning or sensitivity to touch. About 1 in 8 people on the higher doses reported it, compared with about 1 in 100 on placebo. Researchers are still working out why it happens. Overall, 11.3% of people on the top dose stopped because of side effects, versus 4.9% on placebo.

Losing a lot of weight quickly also means losing some muscle along with fat, which is true of all strong weight-loss medicines. Eating enough protein and doing strength training help protect muscle.

When can you get it?

Not yet. Eli Lilly plans to ask the FDA for approval in the first quarter of 2027. A standard FDA review usually takes about a year, so if all goes well, retatrutide could reach pharmacies around 2028. That timing is an estimate, not a promise.

In the meantime, you may see "retatrutide" sold online as a "research peptide". These products are not the medicine tested in the trials. They are unregulated, may contain the wrong dose or impurities, and are not meant for people. The safest way to get retatrutide today is to join a clinical trial.

The bottom line

Retatrutide shows that medicines can now produce weight loss once reached mainly through surgery. It will likely suit people who need large amounts of weight loss and can tolerate the side effects. For many people, the medicines already available may be enough. See how it lines up against them in our retatrutide profile.