How to reconstitute Retatrutide — visual step-by-step

What is reconstitution and why it matters for Retatrutide

Retatrutide (LY3437943) is a triple GIP/GLP-1/glucagon receptor agonist currently in Phase 3 clinical trials. It is a 36-amino-acid peptide with a C20 fatty diacid modification — similar to semaglutide’s lipidation strategy — that enables once-weekly dosing. Research vials ship as lyophilized powder. Because retatrutide is a large, lipidated peptide, reconstitution technique is critical: the fatty acid modification can cause the powder to dissolve more slowly, and mechanical disruption (shaking, jetting water) increases the risk of aggregation. This guide provides a careful, SVG-illustrated protocol for research use.

Internal links: see the Retatrutide peptide profile at /peptides/retatrutide, the dosage guide for research-dose reference, and /methodology.

Materials required

Gather: (1) Retatrutide research vial — commonly 5 mg or 10 mg lyophilized powder. (2) Bacteriostatic water for injection, 30 mL multi-dose vial. (3) Two 1 mL U-100 insulin syringes (a 3 mL syringe may be useful for larger-volume draws). (4) Two 70% IPA alcohol swabs. (5) Clean, flat workspace. (6) Sharps disposal container. (7) Permanent marker and adhesive label. (8) Refrigerator for immediate post-reconstitution storage.

Step-by-step reconstitution protocol

Step 1 — Verify materials (see Diagram 1)

Inspect the retatrutide vial for white or off-white lyophilized powder with no visible moisture. Inspect the BAC water vial for clarity and confirm it is within its use-by date. Wash hands for at least 20 seconds. Open all supplies but do not remove needle caps until ready to use.

Step 2 — Swab both septa

Swab the BAC water septum with 70% IPA in a single outward stroke. Allow 10–15 seconds to air-dry. Repeat with a fresh swab on the retatrutide vial. Both septa must be fully dry before needle insertion.

Step 3 — Draw bacteriostatic water (see Diagram 2)

Insert a fresh needle into the BAC water septum and invert the vial. Draw the target volume. For 5 mg retatrutide: 2.0 mL gives 2,500 mcg/mL; 5.0 mL gives 1,000 mcg/mL. For 10 mg retatrutide: 2.0 mL gives 5,000 mcg/mL; 4.0 mL gives 2,500 mcg/mL. Select the volume that places your weekly research dose in a syringe draw of 20–100 units for practical accuracy. Confirm no air bubbles in the syringe.

Step 4 — Introduce water slowly against the glass wall (see Diagram 3)

Tilt the retatrutide vial at 45 degrees. Insert the needle and direct the tip at the inner glass wall. Introduce the bacteriostatic water in a slow, continuous stream down the wall — not directly onto the powder. Retatrutide’s C20 fatty diacid modification makes it susceptible to aggregation from mechanical stress. Take at least 10–15 seconds to deliver the full volume. Remove the needle when complete.

Step 5 — Gently swirl — allow up to 3 minutes for complete dissolution

Roll the vial slowly between your palms for up to 3 minutes. Retatrutide may dissolve more slowly than shorter peptides due to its lipid modification. Do not shake. If dissolution is incomplete after 3 minutes, place the vial upright in the refrigerator for 15–30 minutes, then gently swirl again. The finished solution should be clear and colorless to slightly yellow.

Step 6 — Label and refrigerate immediately (see Diagram 4)

Label the vial with peptide name, concentration, reconstitution date, and 28-day expiry date. Refrigerate at 2–8°C immediately. Retatrutide in solution should be treated with the same cold-chain discipline as semaglutide or tirzepatide. Do not freeze.

Dose math: translating research doses to U-100 syringe units

Example — 5 mg vial in 2.0 mL BAC water: 2,500 mcg/mL = 25 mcg per unit on U-100. Research dose of 1 mg = 40 units. Research dose of 2 mg = 80 units. Research dose of 4 mg = 160 units (requires two draws). Example — 10 mg in 4.0 mL: 2,500 mcg/mL = same math as above. In the TRIUMPH-1 Phase 3 trial, retatrutide doses studied were 4 mg, 8 mg, and 12 mg weekly. For each of these, 2,500 mcg/mL gives 160, 320, and 480 units respectively (the latter requiring multiple draws or a larger-volume syringe).

Storage post-reconstitution

Reconstituted retatrutide: refrigerate at 2–8°C in bacteriostatic water for up to 28 days. Protect from light. Do not freeze. This guidance follows the USP <797> sterile compounding standards for multi-dose vials with benzyl alcohol preservative. Always inspect before use — discard if cloudy or particulate.

Common mistakes to avoid

Frequently asked questions