GLP-1 vs Dual vs Triple Agonists: What the Research Shows
In less than five years, obesity medicine has moved from one-hormone drugs to molecules that hit two and now three hormone receptors at once. This guide explains the differences between single (GLP-1), dual (GIP/GLP-1) and triple (GIP/GLP-1/glucagon) agonists, and summarizes what the major trials have — and have not — shown.
Key facts
- Single agonist: semaglutide (Wegovy) — about 15–21% average weight loss depending on dose and formulation.
- Dual agonist: tirzepatide (Zepbound) — 20.2% vs 13.7% for semaglutide in the head-to-head SURMOUNT-5 trial.
- Triple agonist: retatrutide — 28.3% at 80 weeks in phase 3 TRIUMPH-1 (efficacy estimand); still investigational and not FDA-approved.
- Trials differ in length, population and statistical method, so cross-trial comparisons are only approximate.
Incretin hormones in plain English
- GLP-1 (glucagon-like peptide-1) is released by the gut after eating. It boosts insulin release when blood sugar is high, slows stomach emptying and acts on the brain to reduce appetite.
- GIP (glucose-dependent insulinotropic polypeptide) is another gut hormone that stimulates insulin. Adding GIP activity to GLP-1 appears to improve tolerability and increase weight loss.
- Glucagon usually raises blood sugar, but at the receptor level it also increases energy expenditure and fat burning in the liver. Combined with GLP-1 and GIP, its glucose-raising effect is offset.
- Amylin is co-released with insulin and promotes fullness. It is the partner hormone in newer combinations such as CagriSema and amycretin.
Single agonists: semaglutide, liraglutide and the new pills
Semaglutide is the best-studied GLP-1 drug. In the SELECT trial of 17,604 adults with heart disease and overweight or obesity (without diabetes), semaglutide 2.4 mg lowered the risk of major cardiovascular events by 20% (hazard ratio 0.80), which led to a heart-protection indication for Wegovy.
The field has also moved to oral options and higher doses:
- Wegovy pill (oral semaglutide 25 mg), FDA-approved December 22, 2025: 16.6% weight loss vs 2.7% on placebo at 64 weeks in OASIS 4 (trial-product estimand).
- Wegovy HD (semaglutide 7.2 mg), approved March 19, 2026: about 20.7% mean weight loss in STEP UP, according to Novo Nordisk.
- Foundayo (orforglipron), Lilly’s once-daily non-peptide GLP-1 pill, approved April 1, 2026: 11.2–12.4% weight loss at the top dose in ATTAIN-1, depending on the estimand.
Dual agonists: tirzepatide (GIP + GLP-1)
Tirzepatide is the first dual GIP/GLP-1 agonist. In SURMOUNT-5, the first head-to-head obesity trial between the two leading drugs, tirzepatide produced 20.2% weight loss versus 13.7% for semaglutide at 72 weeks (751 participants).
It also expanded what these drugs treat: in December 2024 the FDA approved Zepbound as the first medicine for moderate-to-severe obstructive sleep apnea in adults with obesity. In the SURPASS-CVOT trial in type 2 diabetes with heart disease, tirzepatide was non-inferior to dulaglutide on major cardiovascular events (12.2% vs 13.1%), though not statistically superior.
Triple agonist: retatrutide (GIP + GLP-1 + glucagon)
Retatrutide adds glucagon-receptor activity. Its results so far:
- Phase 2 (NEJM, 2023): 24.2% weight loss at 48 weeks on 12 mg.
- Liver fat (Nature Medicine, 2024): 82.4% relative reduction at 24 weeks; 86% of participants on 12 mg reached normal liver fat — an effect consistent with the glucagon component.
- TRIUMPH-1 (phase 3, 2026): 28.3% at 80 weeks (efficacy estimand), 25.0% counting all randomized participants.
The details are in our retatrutide clinical trial explainer. Retatrutide is not FDA-approved; Lilly plans to file in the first quarter of 2027.
Amylin combinations and other next-generation candidates
- CagriSema (cagrilintide + semaglutide): 20.4% vs 3.0% for placebo at 68 weeks in REDEFINE 1. Novo Nordisk submitted it to the FDA in December 2025 and expects a decision in the fourth quarter of 2026. In REDEFINE 4 it did not meet non-inferiority against tirzepatide 15 mg.
- Amycretin (a single GLP-1 + amylin molecule): phase 3 “AMAZE” program started in 2026.
- MariTide (Amgen, monthly dosing): up to about 20% weight loss at 52 weeks in phase 2; phase 3 MARITIME results are expected in 2027.
Comparing trials fairly
Headline percentages are tempting to line up side by side, but:
- Duration differs — 48, 64, 68, 72 and 80 weeks. Longer trials usually show more weight loss.
- Populations differ — people with type 2 diabetes consistently lose less weight than people without it.
- Estimands differ — the “efficacy” estimand (people who stayed on treatment) gives higher numbers than the “treatment-regimen” estimand (everyone randomized).
Only head-to-head trials settle the question. SURMOUNT-5 did so for tirzepatide versus semaglutide; for retatrutide, TRIUMPH-5 (vs tirzepatide) and TRANSCEND-T2D-2 (vs semaglutide) are still pending.
Beyond weight: heart, liver, sleep apnea and joints
| Area | Evidence so far |
|---|---|
| Cardiovascular | Semaglutide reduced major cardiovascular events by 20% in SELECT; retatrutide’s TRIUMPH-Outcomes trial (about 10,000 participants) runs to 2029. |
| Liver (MASH) | Wegovy received accelerated approval for MASH with fibrosis in August 2025; retatrutide shows large liver-fat reductions in phase 2. |
| Sleep apnea | Zepbound approved December 2024; retatrutide reduced apnea events in a TRIUMPH-1 substudy. |
| Knee osteoarthritis | Retatrutide reduced knee pain scores by about 75% in TRIUMPH-4. |
In January 2026, the FDA also asked for suicidal-ideation warnings to be removed from GLP-1 weight-loss drug labels after a meta-analysis of 91 trials found no increased risk.
Safety trade-offs as potency rises
More receptors and more weight loss come with more side effects. Gastrointestinal effects (nausea, diarrhea, vomiting) are common to every drug in this class and rise with dose. Retatrutide has shown a notable rate of dysesthesia (abnormal skin sensations) — up to 20.9% on 12 mg in TRIUMPH-4 — and up to 18.2% of participants on the top dose stopped treatment because of adverse events.
Why it matters in the US
According to the CDC’s National Center for Health Statistics, 40.3% of US adults had obesity and 9.4% had severe obesity in 2021–2023. In December 2025, the World Health Organization issued its first guideline on GLP-1 medicines for obesity, a conditional recommendation for adults.
Approved options — semaglutide and tirzepatide in injectable form, and now two oral pills — are available by prescription. Retatrutide remains investigational: the FDA states it cannot be compounded and warns consumers about “research use only” products. If you follow the research-peptide market, read how we rate retatrutide vendors and see our current vendor ranking.
Sources: Lincoff et al., NEJM 2023 (SELECT); SURMOUNT-5, NEJM 2025; SURPASS-CVOT, NEJM 2025; REDEFINE 1, NEJM 2025; ATTAIN-1, NEJM 2025; FDA press announcements (December 2024, August 2025, January 2026, March 2026, April 2026); Novo Nordisk and Eli Lilly disclosures; CDC NCHS Data Brief 508; WHO.