Reta: Benefits, Side Effects, and the Latest Research

Peptide Profiles — 2026-05-02

Reta (LY3437943) is the most-studied triple receptor agonist in the GP-1 class, simultaneously engaging the GP-1, GIP, and glucagon receptors. Where sema is a single agonist and triz is a dual agonist, reta adds glucagon receptor activation — a third metabolic lever that shifts both energy intake and energy expenditure. This article summarizes the observed benefits, the reported side-effect profile, and the state of the research as of 2026.

How Reta Works

Reta is a synthetic 39-amino-acid peptide engineered to bind three incretin and glucagon-family receptors at once.

GP-1 receptor Drives insulin secretion in a glucose-dependent manner, slows gastric emptying, and reduces appetite via central pathways. This is the same axis that sema and liraglutide engage.

GIP receptor Improves insulin sensitivity, modulates lipid handling in adipose tissue, and appears to blunt some of the GI side effects associated with pure GP-1 agonism — a pattern first observed with triz.

Glucagon receptor This is the differentiating axis. Glucagon receptor agonism increases resting energy expenditure, promotes hepatic fat oxidation, and amplifies thermogenesis. Combined with GP-1-driven appetite suppression, the result in trials is a larger net energy deficit than is seen with single- or dual-agonist peptides.

Observed Benefits in Research

Weight loss The headline result from the Phase 2 trial (NEJM, 2023) was a mean placebo-adjusted body-weight reduction of approximately 24.2% at 48 weeks at the 12 mg dose, with a meaningful share of participants exceeding 30%. These magnitudes are larger than anything previously reported for a single peptide compound.

Glycemic control Phase 2 data in adults with type 2 diabetes (Lancet, 2023) showed HbA1c reductions of ~2.0 percentage points at higher doses, with a substantial fraction of participants reaching non-diabetic A1c ranges.

Hepatic fat A separate Phase 2 trial in MASLD (formerly NAFLD) reported >80% relative reductions in liver fat at the 8 mg and 12 mg doses, with the majority of participants achieving normal liver-fat content. The glucagon component is widely credited for this effect.

Cardiometabolic markers Across trials, reta has produced consistent improvements in: - Systolic blood pressure - Triglycerides and non-HDL cholesterol - Fasting insulin and HOMA-IR - Waist circumference and visceral adiposity proxies

Body composition DEXA substudies suggest that fat mass loss accounts for the majority of the weight reduction, with lean-mass loss broadly proportional to what would be expected with any large negative energy balance — not disproportionately accelerated.

Reported Side Effects

The side-effect profile is dominated by gastrointestinal adverse events, consistent with the GP-1 receptor mechanism.

Common (≥10% in trials) - Nausea - Diarrhea - Vomiting - Constipation - Decreased appetite (expected, but flagged when severe)

These tend to be dose-dependent, most prominent during dose escalation, and attenuate with continued exposure. Slow titration substantially reduces incidence.

Less common but notable - Heart rate increase — modest mean increases in resting heart rate (typically 3-7 bpm) similar to other incretin agonists. - Transient transaminase elevations — usually mild and reversible. - Injection-site reactions — generally mild. - Mild hyperglycemia at very high doses in some non-diabetic participants — attributed to glucagon receptor agonism and seen mainly during rapid titration.

Theoretical and monitored - Pancreatitis: not clearly elevated in trials so far, but monitored as a class effect. - Gallbladder events: a known class signal across GP-1 agonists, requires longer-term follow-up. - Thyroid C-cell tumors: rodent class warning; no human signal observed. - Diabetic retinopathy progression with rapid glucose lowering: monitored as a class effect.

State of the Research

Phase 3 program (TRIUMPH) Lilly's Phase 3 program is broad, with the major arms covering: - TRIUMPH-1 — obesity in adults without diabetes - TRIUMPH-2 — obesity with type 2 diabetes - TRIUMPH-3 — obesity with established cardiovascular disease - TRIUMPH-4 — long-term durability and weight maintenance - Companion trials in MASH/MASLD, knee osteoarthritis with obesity, and obstructive sleep apnea

Readouts have been arriving on a rolling basis through 2025 and 2026. As of mid-2026, reta remains investigational and is not approved for clinical use in any jurisdiction.

Open research questions - Long-term durability of weight loss after discontinuation - Comparative head-to-head data versus triz - Optimal titration schedules to minimize GI burden - Sub-population response heterogeneity (genetics, baseline metabolic status) - Cardiovascular outcomes data — pending from longer trials

Practical Research Considerations

For laboratory and research-use handling: - Store lyophilized peptide at -20°C for long-term stability; 2-8°C for short-term working stock - Reconstitute with bacteriostatic water; protect reconstituted vials from light and use within recommended stability windows - Verify purity (>98%) via COA before beginning any research protocol - Document lot number, reconstitution date, and storage conditions for reproducibility

Reta remains one of the most active areas of metabolic peptide research. The benefit signals are large and consistent across trials, the side-effect profile is well-characterized and class-typical, and the Phase 3 program will determine how it ultimately compares to existing dual- and single-agonist options.

Disclaimer: All information presented in this article is for educational and informational purposes only. Platinum Biolabs does not promote or endorse the use of peptides for human consumption. All products sold by Platinum Biolabs are intended strictly for laboratory and research use only. Consult a qualified healthcare professional before making any health-related decisions.