Retatrutide + Cagrilintide Dosage: Stack Protocol

The retatrutide + cagrilintide stack is the most aggressive metabolic peptide combination community sources currently describe — a triple-agonist GLP-1/GIP/glucagon backbone (retatrutide) layered with a long-acting amylin analog (cagrilintide). Each compound has its own Phase 2 and Phase 3 dataset; the combination has none. Everything below is reported from per-compound clinical literature and self-organized community protocols.

Research-context information only. Retatrutide and cagrilintide are both investigational drugs not approved by the FDA. Protocols, doses, and reactions reported below come from published clinical trials (each compound studied separately and one combination not involving retatrutide) and self-reported community sources. No clinical trial has formally tested the retatrutide + cagrilintide combination as of May 2026. This article reports what has been documented, not what should be done. Possession or use of investigational drugs outside an authorized clinical trial may be illegal in your jurisdiction. Consult a licensed physician for personal medical decisions.

The core question this guide answers: how community references stage the stack — when cagrilintide gets added, how it's titrated alongside retatrutide, and how the two are reportedly injected to keep the gastrointestinal burden manageable.

Quick Reference: Reported Stack Protocol

Community-reported sequencing: Protocols commonly begin with retatrutide alone. Once retatrutide is tolerated at the 2 mg/week step — typically 8–12 weeks in — community references describe introducing cagrilintide at 0.25 mg/week and following a separate 4-week titration to maintenance.

Why Stack Sequencing Matters

Both retatrutide and cagrilintide slow gastric emptying — but through entirely different signaling pathways. Retatrutide does it via GLP-1 receptor activation in the gut and CNS; cagrilintide does it via the amylin receptor (AMY1R/AMY3R heterodimers) in the area postrema. Activating both at full dose simultaneously, with no titration runway, is what community sources describe as the failure mode that drives discontinuation.

The reported sequencing solution: get one pathway saturated and stable first, then layer the second on a fresh titration. This is also the structure Novo Nordisk's own investigational semaglutide+cagrilintide combination used in REDEFINE 1 (Garvey et al., NEJM 2025) — both components stepped in parallel through a 16-week ramp rather than introduced together at maintenance.

Component Titration Schedules (As Reported in Trial and Community Sources)

Retatrutide Titration

The Jastreboff et al. Phase 2 trial (NEJM 2023) used a structured ramp to 12 mg/week — but at trial doses of 8 mg and 12 mg, dropout from gastrointestinal events was substantial. Community-reported retatrutide protocols deliberately stay below trial peak:

Self-reported maintenance doses cluster at 2-4 mg/week. The 12 mg trial dose is rarely described in community references because the GI burden was the rate-limiting factor in the trial.

Cagrilintide Titration (Once Retatrutide Stable)

Cagrilintide titration described in community sources mirrors the REDEFINE 1 schedule (Garvey et al., 2025):

The Lau et al. Phase 2 dose-finding trial (Lancet 2021) showed clear dose-response from 0.3 mg up to 4.5 mg/week, but 2.4 mg is the dose Novo Nordisk advanced into Phase 3 and is the most commonly self-reported community ceiling.

Same-Day vs Split-Day Injection (Community-Reported Patterns)

Community sources describe two patterns for combining the weekly injections.

Same-day, different sites (most common): Both injections delivered the same day each week, at separate subcutaneous sites — typically retatrutide in the abdomen and cagrilintide in the thigh, or rotated weekly. Reported rationale: peak GI effect is concentrated to a single day rather than smeared across the week.

Split-day (community variant): Retatrutide on day 1, cagrilintide on day 4. Reported rationale: less compounded peak nausea, smoother appetite suppression curve. Reported tradeoff: two "shot days" per week instead of one.

Neither pattern has been studied in a published trial. Both are derived from how community users have organized the schedule themselves. The REDEFINE 1 trial used a co-administered single-injection product, which is not the same as either of these patterns.

Pre-Mixed Blend Vials: 12.5/2.5 vs 20/4

Some research vendors stock pre-mixed retatrutide + cagrilintide vials at a fixed ratio. As of May 2026, two configurations are common:

Both maintain the same 5:1 mass ratio of retatrutide to cagrilintide. At 4 mg retatrutide / 0.8 mg cagrilintide per week (the upper end of community-reported maintenance for both), the smaller vial provides roughly 3 weeks at maintenance and the larger vial roughly 5 weeks. Pre-mixed vials lock the ratio — they cannot be used during the staged titration described above without overdosing one component or underdosing the other.

For staged titration, separate retatrutide and cagrilintide vials are what most community sources describe using. Pre-mixed vials are reportedly used once both components have already been titrated to a steady ratio.

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Reconstitution Quick Reference

Community reconstitution resources describe the following example calculations for common research-vendor vial sizes (BAC water volumes and resulting concentrations vary by protocol):

For pre-mixed 12.5 mg / 2.5 mg blend in 2 mL BAC water → 7.5 mg/mL total (6.25 mg/mL retatrutide + 1.25 mg/mL cagrilintide). At a "1 mg retatrutide + 0.2 mg cagrilintide" combined dose: 0.16 mL = 16 units.

Both vials require refrigerated storage at 2-8°C after reconstitution — a dedicated mini fridge keeps temperatures stable and avoids the door-zone fluctuations of a household refrigerator. The full step-by-step reconstitution math, syringe diagrams, and storage rules live in the Retatrutide+Cagrilintide Reconstitution Guide.

Where These Numbers Come From

The retatrutide + cagrilintide combination has no published clinical trial as of May 2026. Everything in the stack protocol section is assembled from per-compound trial data plus community-protocol sequencing.

Retatrutide solo data. The Jastreboff et al. Phase 2 trial (NEJM 2023) reported 24.2% mean weight loss at 48 weeks with 12 mg/week retatrutide, with gastrointestinal adverse events rising sharply at the 8 mg and 12 mg doses. The TRIUMPH-4 Phase 3 trial in obesity with knee osteoarthritis later reported 28.7% mean weight loss at 68 weeks with retatrutide 12 mg/week, and identified a dose-related dysesthesia (nerve-tingling) signal in 8.8% of 9 mg and 20.9% of 12 mg patients (Bays et al., 2025).

Cagrilintide solo data. The Lau et al. Phase 2 trial (Lancet 2021) tested cagrilintide 0.3 mg through 4.5 mg/week as monotherapy and reported a clear dose-response, with 10.8% mean weight loss at 4.5 mg/week at 26 weeks. 2.4 mg was the dose advanced into Phase 3 because the efficacy/tolerability ratio peaked there.

Closest-analog combination data. REDEFINE 1 (Garvey et al., NEJM 2025) is the only Phase 3 trial of an amylin + incretin co-administered combination, pairing cagrilintide 2.4 mg with semaglutide 2.4 mg. It reported 22.7% mean weight loss at 68 weeks vs 16.1% for semaglutide alone and 11.8% for cagrilintide alone — clear additive benefit. The Frias et al. Phase 2 trial in type 2 diabetes (Lancet 2023) also showed superior weight loss for the combination versus either monotherapy.

The reta+cagri stack borrows the REDEFINE titration cadence and applies it to a stronger incretin backbone. Whether the additive gain seen with cagrilintide+semaglutide replicates against the already-stronger retatrutide is an open empirical question.

Stacking with the Broader Metabolic Toolkit

Some community sources reference layering this stack with non-incretin compounds. None of these have been formally tested with retatrutide+cagrilintide. Reported community pairings include:

Stacking beyond reta+cagri compounds GI tolerability concerns with reta+cagri-specific safety questions and is rarely described in conservative community references.

Side Effects on the Stack

The full safety picture lives in the Retatrutide+Cagrilintide Stack Side Effects article. Headline points:

• Both compounds independently produce dose-related nausea, vomiting, constipation, and decreased appetite.
• Retatrutide carries a dose-related dysesthesia signal at 9-12 mg/week (Phase 3) — community doses stay well below this.
• Cagrilintide had one of the lowest GI odds ratios among incretin-class compounds in a 2025 network meta-analysis, but combination GI burden has not been formally quantified.
• Conservative titration (4-week steps, both compounds) is what community sources consistently describe as the approach that keeps the stack tolerable.