Reta vs Sema: A Research Comparison

Comparisons — 2026-05-28

"Reta vs sema" pits the original single-receptor GP-1 agonist against the next-generation triple agonist. Sema is the most-studied molecule in the class; reta is the most potent on weight-loss magnitude. Here is how they compare for research purposes.

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Mechanism: One Receptor vs Three

Sema activates the GP-1 receptor only — appetite suppression, glucose-dependent insulin secretion, delayed gastric emptying.
Reta activates GP-1 + GIP + glucagon. It keeps everything sema does and adds GIP (insulin sensitivity, adipose signaling) and glucagon (energy expenditure, hepatic fat oxidation).

Sema works only on the intake side of energy balance. Reta works on intake *and* output.

Weight Loss Magnitude

Compound	Receptors	Trial	Top-dose weight loss	Duration
Sema (2.4 mg)	GP-1	STEP 1	~14.9%	68 weeks
Reta (12 mg)	GP-1 + GIP + glucagon	Jastreboff Phase 2	~24.2%	48 weeks

At its top obesity dose, sema delivers ~15% — a landmark result when it published. Reta's triple mechanism pushed that to ~24% in less time. Even reta's lowest 4 mg arm (~17%) exceeded sema's top dose.

Glycemic Control

Sema (1 mg): ~1.5–1.8% HbA1c reduction (SUSTAIN)
Reta (12 mg): ~2.0–2.2% HbA1c reduction (Phase 2 T2D)

Reta edges sema on glucose, but the absolute gap is smaller than the weight-loss gap. Sema's enormous, decade-long safety dataset is its standout advantage.

Tolerability

Both share GP-1 class side effects (nausea, GI effects during titration). Reta adds glucagon-mediated effects — mild heart rate elevation, transient transaminase changes, and higher GI burden at top doses. Sema, with one receptor and a lower dose ceiling, generally has lower discontinuation rates.

Protocol Snapshot

Reta	Sema
Receptors	GP-1 + GIP + glucagon	GP-1 only
Frequency	Weekly	Weekly
Half-life	~6 days	~7 days
Trial weight loss	~24%	~15% (2.4 mg)
Approved	No (research only)	Yes
Long-term safety data	Phase 2	Decades

Which for Which Research Question?

Sema — when you want the best-characterized GP-1 baseline, a long safety record, and a modest, well-defined effect size.
Reta — when maximum weight-loss magnitude or the glucagon arm is the endpoint.

Do not stack them Both activate GP-1; combining is redundant and raises GI burden without added benefit. Pick the one that fits the question.

Bottom Line

Sema is the proven single-receptor benchmark; reta is the higher-magnitude triple agonist with a thinner safety record. Choose sema for a characterized baseline, reta for maximum effect or glucagon-arm research. See also reta vs triz and reta vs Wegovy.

Code WELCOME at checkout unlocks 35% off Reta 10mg, Reta 20mg, Sema 10mg, and the Metabolic Stack. Every vial ships with a batch-matched COA showing 99%+ HPLC purity — matched material for clean comparison work.

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