Retatrutide vs CagriSema: Triple Agonist vs the Amylin Combination

Retatrutide and CagriSema are the two most talked-about next-generation obesity drugs in 2026, and they represent completely different strategies for exceeding semaglutide.

Retatrutide solves the problem by adding two more receptors on top of the GLP-1 backbone. It agonises GLP-1, GIP and glucagon simultaneously. The glucagon arm is the differentiator: it drives hepatic fatty acid oxidation, raises basal metabolic rate through FGF21 and uncoupling protein 1, and produces sympathetic activation that shows up on wearable heart rate data. TRIUMPH-1 topline reports 28.3 percent weight loss at 12mg over 80 weeks, with the BMI 35+ extension cohort reaching 30.3 percent at week 104.

CagriSema solves the same problem differently. It keeps semaglutide as the GLP-1 backbone and adds cagrilintide, a dual amylin and calcitonin receptor agonist, in a fixed-dose weekly injection. Amylin acts on the area postrema to increase satiety through a mechanism completely separate from incretin biology. REDEFINE 1 (Garvey 2025, NEJM) reports 20.4 percent weight loss on the combination over 68 weeks, versus 14.9 percent on semaglutide alone and 11.5 percent on cagrilintide alone.

The cross-trial magnitude difference is real: retatrutide's 28.3 percent versus CagriSema's 20.4 percent, roughly 8 percentage points on similar trial durations. But the two drugs have different regulatory paths, different side effect profiles, and different mechanistic implications for future combinations.

Receptor pharmacology:

• Retatrutide: GLP-1R + GIPR + GCGR, three receptors on one molecule.
• CagriSema: GLP-1R (semaglutide) plus AMLNR + CALCR (cagrilintide), four receptors across two molecules in one injection.
• Retatrutide's glucagon arm is unique to it. CagriSema's amylin arm is unique to it. There is no overlap.

Head-to-head weight loss (no direct trial exists):

• Retatrutide 12mg TRIUMPH-1: 28.3 percent at 80 weeks (BMI 35+ extension reached 30.3 percent at week 104).
• CagriSema REDEFINE 1: 20.4 percent over 68 weeks (treatment-policy), 22.7 percent on trial-product estimand.
• The gap is roughly 8 percentage points favouring retatrutide, but trial durations and populations differ.

Preclinical head-to-head does exist:

• Petersen et al. 2026 (Nature Metabolism) compared cagrilintide plus retatrutide, cagrilintide plus semaglutide (CagriSema), and cagrilintide plus tirzepatide at matched molar doses in obese male rats. Cagri plus reta produced 17.6 percent weight loss over 14 days, CagriSema produced 13.1 percent. The finding suggests the semaglutide arm of CagriSema is doing less work than the equivalent slot in a triple agonist would.

Regulatory status (September 2026):

• Retatrutide: investigational. FDA submission expected late 2026, potential approval late 2027.
• CagriSema: FDA NDA filed by Novo Nordisk in December 2025 based on REDEFINE 1 and REDEFINE 2. Decision expected Q4 2026.
• CagriSema is closer to the market by roughly a year.

Cardiovascular tolerability:

• Retatrutide resting HR rise: +3.46 bpm pooled (Zhang 2026 network meta-analysis), reaching +5 to +10 bpm at 8 to 12 mg in Phase 2, peaking around week 24.
• CagriSema HR effect: driven by the semaglutide arm alone, roughly +2 to +3 bpm. Amylin does not add.
• Retatrutide is the tougher cardiac profile.

Gastrointestinal burden:

• Retatrutide 12 mg TRIUMPH-1: nausea 42.4 percent, vomiting 25.3 percent, diarrhoea 32 percent, constipation 26.1 percent.
• CagriSema REDEFINE 1: gastrointestinal adverse events 79.6 percent versus 39.9 percent on placebo.
• CagriSema's higher headline GI number reflects both amylin's contribution to gut motility slowing and the additive effect on top of semaglutide.

Novel side effects unique to each:

• Retatrutide: dysesthesia (burning, tingling skin) at 12.5 percent on 12mg vs 0.9 percent placebo. Class-new signal.
• CagriSema: no unique signal beyond the class-known GLP-1 and pancreatitis warnings.

AE-driven discontinuation:

• Retatrutide 12mg: 11.3 percent in TRIUMPH-1.
• CagriSema: not itemised in trial-product estimand from published summaries but running around 10 percent based on REDEFINE 5 data.

Body composition:

• Retatrutide Phase 2 body composition (Coskun 2025) preserved roughly 75 percent fat / 25 percent lean of total loss.
• REDEFINE 1 DXA substudy (conference-only, Ravussin 2025): CagriSema 66.9 percent fat / 33.1 percent lean, worse than semaglutide alone at 69.7 / 30.3. Cagrilintide alone was worst at 62.9 / 37.1.
• Retatrutide has the better body composition profile of the two.

Cost and access:

• Retatrutide: grey market only. Approximately USD $80 to $200/month from research peptide vendors, no third-party purity validation.
• CagriSema: not yet marketed. Expected pricing similar to Wegovy at USD $1,000+/month once launched.

Combining them (Petersen 2026 extension of the story):

• The rat data suggests cagrilintide plus retatrutide beats CagriSema plus retatrutide, because the semaglutide in CagriSema becomes redundant once retatrutide is providing the GLP-1 tone.
• No human trial of retatrutide plus cagrilintide exists.

Choose retatrutide if:

• Maximum weight loss magnitude is the primary goal (28.3 vs 20.4 percent).
• You have severe MASLD or hypertriglyceridaemia. Retatrutide's 82 percent liver fat reduction (Sanyal 2024) is unmatched by any other class.
• Body composition matters more than headline weight and you want the better fat-to-lean split (75/25 vs CagriSema's 67/33).
• You accept the dysesthesia signal, the higher HR rise, and grey-market sourcing risk.

Choose CagriSema (when it approves) if:

• Regulated pharmaceutical access matters. You need an actual prescription from your endocrinologist, insurance coverage potential, and pharmacy-grade sourcing.
• You are on a cardiac risk profile that cannot absorb an extra +5 to +10 bpm.
• You want two mechanisms hitting satiety independently (incretin plus amylin) rather than one triple agonist.
• You are cardiovascular event risk-averse and want the safety data from a Phase 3 program that completed roughly a year earlier than TRIUMPH-1.

It does not matter which you pick for:

• Type 2 diabetes HbA1c reduction. Both reach roughly 2 percentage points of reduction at max dose.
• Baseline glycaemic monitoring protocol. Both need the same lipase, HbA1c and lipid panel schedule.

Both need the same monitoring core: lipase at week 4, 12, 24 for pancreatitis surveillance. HbA1c and full lipid panel at week 12 and 24. Resting heart rate from a wearable continuously. TSH baseline and at 12 weeks. On CagriSema, monitor for hypoglycaemia specifically if the patient is on background insulin or a sulfonylurea. On retatrutide, monitor for dysesthesia and resting HR climb.