GLP-1 / GIP / Glucagon Triple Agonists

GLP-1 / GIP / glucagon triple agonists are a class of obesity and diabetes drugs that activate three different hormone receptors with a single molecule. GLP-1 reduces appetite, GIP amplifies the insulin response and may dampen nausea, and glucagon prompts the body to burn stored fat, including fat in the liver. Eli Lilly's retatrutide is the lead drug in the class and the first to produce Phase 3 data. Its flagship Phase 3 obesity trial, TRIUMPH-1, read out in May 2026 with an average 28.3% weight loss at the top dose, the largest any obesity drug has shown in a pivotal trial to date. Across its Phase 3 program, retatrutide also surfaced a side effect that Phase 2 had not shown: dysesthesia, a persistent unusual skin sensation. Several other triples are in earlier development, but the class's direction over the next year largely turns on the remaining retatrutide Phase 3 readouts.

How triple agonists work

The core idea is that GLP-1 (glucagon-like peptide-1), GIP (glucose-dependent insulinotropic polypeptide), and glucagon each have their own distinct effects, with some overlap, and stacking all three in one molecule presses more levers than mono-agonists or dual agonists can.

GLP-1 and GIP are both incretins. After a meal, both signal the pancreas to release insulin in proportion to how much glucose just hit the bloodstream. What sets the two hormones apart is what each does beyond insulin.

Beyond insulin, GLP-1 acts strongly on appetite and digestion. It's one of the signals that tells the brain you're full and slows the rate at which food leaves the stomach. Drugs in the GLP-1 family (Ozempic, Wegovy, and the rest) activate that signal more strongly than the body does on its own, and that is how they reduce hunger and produce weight loss.

Beyond insulin, GIP makes several other contributions. Brainstem GIP receptors are increasingly thought to soften the nausea that comes with GLP-1 drugs, and hypothalamic GIP receptors contribute to appetite regulation alongside GLP-1. GIP also influences how adipose tissue stores and metabolizes fat. Tirzepatide (sold as Mounjaro for diabetes and Zepbound for weight loss), the first approved dual agonist, pairs GLP-1 with GIP. In trials, it has produced more weight loss than GLP-1 drugs alone and, so far, has been better tolerated than the scale of that weight loss would predict.

Glucagon is the more counterintuitive addition. In normal physiology, glucagon raises blood sugar. It is the hormone the pancreas releases when blood glucose drops too low, so adding a glucose-raising signal to a diabetes or obesity drug initially sounds like a bad idea. But at the higher doses a drug reaches, glucagon does two metabolically useful things: it acts directly on the liver to drive hepatic fat oxidation, burning the fat stored in liver cells, and it also appears to raise whole-body energy expenditure (the body burns more calories at rest), though how much that resting-burn effect adds to weight loss in humans is still being worked out. Both GLP-1 and GIP stimulate insulin release in parallel, which offsets glucagon's blood-sugar effect, leaving the dramatic reductions in liver fat (and the added calorie burn) that are emerging as a defining feature of the class (retatrutide's Phase 2 liver-fat data is roughly 82% reduction at 24 weeks on the top dose).

A triple agonist activates all three receptors with a single molecule. The open question across the entire class is whether three levers compound each other's effects, or whether the added complexity mostly adds side effects. Retatrutide's Phase 2 data and Phase 3 readouts have begun to answer the first half of that question. Its Phase 3 safety profile has begun to sharpen the second.

The competitive landscape

Landscape as of June 2026

Retatrutide is the only triple with Phase 3 results so far, and the data has landed. Its flagship obesity trial, TRIUMPH-1 (about 2,300 adults with obesity or overweight and no type 2 diabetes), read out in May 2026: an average 28.3% weight loss at the top 12 mg dose over 80 weeks, in bariatric-surgery territory and higher than any obesity drug has shown in a pivotal trial to date. The more strategically interesting detail was the dose ladder. A middle 9 mg dose produced 25.9%, and even a low 4 mg dose reached nearly 20% weight loss with a side-effect discontinuation rate that actually fell below placebo, reframing retatrutide from a powerful-but-rough drug into something physicians can titrate from a tolerable floor up to a maximal-loss ceiling. An earlier, smaller Phase 3 trial, TRIUMPH-4 (in patients with obesity and knee osteoarthritis), had reported 28.7% weight loss over 68 weeks in December 2025 along with meaningful knee-pain improvement, and a separate Phase 3 diabetes trial from Lilly's TRANSCEND program reported strong blood-sugar and weight-loss results in March 2026.

The Phase 3 program also surfaced a side effect that had not appeared in Phase 2: dysesthesia, a persistent unusual skin sensation most often described as burning or pins-and-needles. The signal is dose-dependent, and its size has varied across trials: about 21 percent of patients on the top 12 mg dose reported it in the smaller TRIUMPH-4 population, but a notably softer 12.5 percent in the flagship TRIUMPH-1 trial (versus well under 1 percent on placebo). In TRIUMPH-4, about 18 percent of top-dose patients discontinued for side-effect reasons overall (versus 4 percent on placebo), though Lilly reported that the dysesthesia events themselves were generally mild and rarely the direct cause. The TRIUMPH-1 dose ladder suggests lower doses may preserve most of the weight loss while keeping that signal down, which is exactly what Lilly is now testing.

Behind retatrutide, the clearest credible contender is UBT251, a triple developed by United Laboratories in China and licensed to Novo Nordisk in March 2025 for markets outside Greater China. In a Phase 2 trial in Chinese patients, UBT251 produced 19.7% weight loss at 24 weeks on the top dose, a pace roughly in line with retatrutide's Phase 2 results at the same six-month mark. Novo is now running a global Phase 1b/2a to confirm those results ahead of late-stage testing. In parallel, Hanmi (a Korean developer) has two triples in development: efocipegtrutide, in Phase 2 for liver disease, and HM15275, in Phase 2 for obesity. Retatrutide itself has a strong Phase 2 liver-disease result on record (about 82% reduction in liver fat at 24 weeks on the top dose), so the liver-disease question for the class is live across multiple programs.

Beyond these, Novo Nordisk's in-house triple has advanced into Phase 2, while Eli Lilly's second triple and Jiangsu Hengrui's first program remain in Phase 1. An earlier triple from Sanofi was discontinued in 2019 for portfolio reasons rather than safety.

The race to watch over the next 12 to 18 months: whether retatrutide's remaining Phase 3 readouts, expected later in 2026, confirm the flagship TRIUMPH-1 efficacy without adding new safety signals, whether the lower doses that looked so clean in TRIUMPH-1 hold up at scale, and whether UBT251 delivers when Novo moves it from Chinese Phase 2 into a global program.

Drugs in this class

Also in this class

• LY4086940 · Eli Lilly · Phase 1
• HRS-4729 · Jiangsu Hengrui (Kailera ex-China, as KAI-4729) · Phase 1

Withdrawn and paused

• SAR441255 (Sanofi) was discontinued in 2019 as part of a broader portfolio review, not for safety reasons. The molecule had only reached Phase 1 trials.

Related and adjacent mechanisms

A few related drug classes don't quite fit the triple-agonist definition but sit close enough to be worth knowing about, especially if you're trying to understand where obesity medicine might be heading.

Drop one receptor: the dual agonists

Subtracting any single receptor from a triple produces a class already in late-stage trials. GLP-1 / GIP duals (tirzepatide and its challengers) drop glucagon. GLP-1 / glucagon duals (survodutide, pemvidutide, mazdutide) drop GIP. Both dual classes have shown substantial weight loss, and the GLP-1 / glucagon duals are also showing strong effects on liver fat. Each class carries its own trade-offs: duals are easier to tune than triples (balancing two receptors is simpler than three), while triples bet that the extra lever is worth the added complexity and new tolerability questions.

Pair GLP-1 with amylin: GLP-1 + amylin combinations

Novo Nordisk has pursued a parallel approach that keeps GLP-1 but swaps in amylin, a separate satiety hormone released from the pancreas alongside insulin. Amylin suppresses appetite through different brain pathways than GLP-1. CagriSema (a fixed-dose combination of semaglutide and cagrilintide) and amycretin (a single molecule that activates both receptors) are both in late-stage testing. Others are testing co-administration, pairing a separate amylin analog with an incretin agonist as two injections rather than building one molecule (AstraZeneca's ASCEND program is the clearest example). The GLP-1 + amylin combinations field guide covers them in detail.

Activate GLP-1, block GIP: MariTide

Not every next-generation obesity drug adds more receptor targets. Amgen's MariTide (maridebart cafraglutide) activates GLP-1 but blocks GIP, the opposite of what triples and most duals do. Both approaches have shown weight loss in trials, and researchers are still working out why opposite actions on the same receptor can both produce similar effects. MariTide is currently in Phase 3 obesity trials. Pfizer is testing the same hypothesis through a different architecture: oral co-administration of a GIPR antagonist (PF-07976016, Phase 2) with one of its early-stage oral GLP-1 candidates.

Frequently asked questions

Recent newsletter coverage

Past pieces from the GLP-1 Observer newsletter that touched on this class.

References