Single, dual, and triple incretin agonists

What "agonism" actually means

Receptor agonism refers to a drug binding and activating a specific receptor. The incretin family contains three receptors of clinical interest: GLP-1 (the workhorse for appetite suppression and glucose-dependent insulin release), GIP (glucose-dependent insulinotropic polypeptide, with effects on adipose tissue and central appetite signaling), and the glucagon receptor (which raises basal energy expenditure when activated and mobilizes hepatic glycogen / lipid).

The simplest molecules in this class — semaglutide and liraglutide — activate only the GLP-1 receptor. Each step up adds another receptor.

Single agonism — GLP-1 alone

Examples: semaglutide (Ozempic / Wegovy), liraglutide (Victoza / Saxenda), dulaglutide (Trulicity).

Single GLP-1 agonists drive appetite suppression, slowed gastric emptying, and glucose-dependent insulin release. Phase 3 weight loss in obesity at semaglutide 2.4 mg averages ~15% over 68–72 weeks. The cardiovascular outcomes data is the strongest in the class — SELECT in particular establishing semaglutide as having a 20% MACE reduction in obesity with established CV disease.

Dual agonism — GLP-1 + GIP

Example: tirzepatide (Mounjaro / Zepbound).

Adding GIP receptor agonism to GLP-1 agonism produced an unexpectedly large step up. SURMOUNT-1 reported ~21% weight loss at 72 weeks at the 15 mg dose — meaningfully greater than semaglutide 2.4 mg in head-to-head comparison.

The mechanistic story for why GIP addition helps is still being characterized. The historical assumption was that GIP agonism contributes additional appetite suppression and adipose-tissue effects. Recent work (most strikingly from the MariTide program) has questioned that assumption, suggesting GIP antagonism may be doing some of the work — meaning the field's understanding of dual receptor strategies remains genuinely open.

Triple agonism — GLP-1 + GIP + glucagon

Example: retatrutide (TRIUMPH program).

Adding glucagon receptor agonism to the GLP-1/GIP combination contributed an additional energy-expenditure mechanism. The Phase 2 TRIUMPH-1 result — ~24% weight loss at 48 weeks — extended the trajectory.

The challenge with glucagon-receptor activation is balancing the energy-expenditure benefit against glucagon's glucose-raising and heart-rate effects. The molecular tuning of receptor affinity ratios is what makes the triple-agonist concept clinically viable.

The dual GLP-1/glucagon path

An alternative configuration — skipping GIP and combining GLP-1 with glucagon — is represented by survodutide, mazdutide, and pemvidutide. These programs prioritize hepatic effects (relevant for MASH) and can compete on weight loss with the dual GIP/GLP-1 strategy.

The inverse — GLP-1 + GIP-receptor antagonism

MariTide (maridebart cafraglutide) takes a striking direction: GLP-1 agonism combined with GIP receptor antagonism. The rationale is that GIP antagonism — not agonism — may be the mechanism that drives the additive weight loss seen when modulating both receptors. Phase 3 will adjudicate the hypothesis at scale.

What this means in practice

• Magnitude of weight loss generally rises with receptor count, though differences narrow at the upper end.
• Cardiovascular outcomes data is most established for semaglutide (SELECT) and accruing for the broader class.
• Tolerability profiles are similar in shape across the class but vary in detail (heart rate effects, GI signature, glucose tolerability with glucagon-arm drugs).
• Indication tuning is increasingly important — MASH-focused programs (pemvidutide, survodutide) are not simply weight-loss-stronger drugs; they are designed for liver-disease endpoints.

Bottom line

The single → dual → triple progression has driven the field's weight-loss ceiling from ~15% with semaglutide toward ~24% with retatrutide in Phase 2, with monthly antibody-conjugate strategies (MariTide) and multi-receptor balances (survodutide, pemvidutide) now competing for indication-specific advantages. The next several years will sort how much further receptor stacking can push outcomes — and where indication-specific molecular design matters more than receptor count.