Retatrutide Dosage Calculator

How Retatrutide Dosage Calculation Works

This retatrutide dosage calculator converts your weekly dose in mg into the exact syringe units to draw. Retatrutide is supplied as a lyophilized (freeze-dried) powder and must be reconstituted with bacteriostatic water (BAC water) before injection. Once reconstituted, the resulting solution has a concentration in micrograms per milliliter (mcg/mL), which you use to calculate how many syringe units to draw for your weekly dose.

The formula is two steps:

1. Concentration (mcg/mL) = Vial size (mg) × 1,000 ÷ BAC water added (mL)
2. Units to draw = (Target dose in mcg ÷ Concentration) × 100 for U-100 syringe

Example: 5 mg vial + 2 mL BAC water = 2,500 mcg/mL. A 4 mg weekly dose = 4,000 mcg. Units to draw: 4,000 ÷ 2,500 × 100 = 160 units on U-100 (1.6 mL). The calculator above performs this automatically — just enter your vial size, BAC water volume, and desired dose.

Retatrutide Dosing Protocol and Titration Schedule

Because retatrutide activates three receptor types (GLP-1, GIP, and glucagon), it is more potent than earlier GLP-1 agonists and requires careful titration to avoid gastrointestinal side effects. Research protocols typically follow a step-up schedule:

• Weeks 1–4: 2 mg/week — starting dose
• Weeks 5–8: 4 mg/week
• Weeks 9–12: 6 mg/week
• Weeks 13–20: 8 mg/week
• Week 20+: Up to 12 mg/week for maintenance

Always consult a licensed healthcare provider before following any peptide protocol. Dose escalation should be paused if significant nausea, vomiting, or other adverse effects occur.

Syringe Unit Reference for Common Retatrutide Doses

The table below shows units to draw on a U-100 syringe for common weekly doses, using a 5 mg vial reconstituted with 2 mL BAC water (2,500 mcg/mL):

• 2 mg/week (2,000 mcg): 80 units on U-100 — 0.80 mL
• 4 mg/week (4,000 mcg): 160 units on U-100 — 1.60 mL
• 6 mg/week (6,000 mcg): 240 units on U-100 — 2.40 mL (consider 10 mg vial or higher concentration)
• 8 mg/week (8,000 mcg): 320 units on U-100 — 3.20 mL (use 10 mg vial + 2 mL for 5,000 mcg/mL = 160 units)

For doses above 4 mg, using a 10 mg vial or adding less BAC water (1 mL instead of 2 mL) keeps injection volumes manageable. Use the peptide reconstitution calculator to find the right BAC water volume for any dose and vial size.

Reconstituting Retatrutide Step by Step

Proper reconstitution technique ensures potency and sterility. Follow these steps:

1. Allow the BAC water and peptide vial to reach room temperature.
2. Wipe both vial stoppers with alcohol swabs and allow to air dry.
3. Draw the desired volume of BAC water into a syringe.
4. Insert the needle and slowly inject BAC water down the side of the vial — not directly onto the peptide cake.
5. Gently swirl until fully dissolved. Do not shake — shaking denatures peptide bonds.
6. Inspect: the solution should be clear and colorless. Discard if cloudy or particulate.
7. Label the vial with date of reconstitution and store refrigerated at 2–8°C.

Retatrutide vs. Semaglutide and Tirzepatide

Retatrutide differs from semaglutide and tirzepatide in its receptor targeting. Semaglutide is a GLP-1 receptor agonist; tirzepatide adds GIP receptor agonism (dual agonist); retatrutide adds glucagon receptor activation on top (triple agonist). The glucagon component may drive additional energy expenditure compared to the dual agonist class. For dose calculation purposes, all three are handled identically — the same vial concentration formula and unit math applies to each. See the semaglutide dosage calculator and tirzepatide dosage calculator for peptide-specific defaults.

Retatrutide Benefits and Clinical Research

Retatrutide's defining advantage over earlier GLP-1 peptides is its triple receptor mechanism. GLP-1 agonism reduces appetite via hypothalamic receptors and slows gastric emptying; GIP receptor activation enhances glucose-dependent insulin secretion and may reduce GI side effects; glucagon receptor activation directly increases energy expenditure and promotes lipolysis. This convergence of three mechanisms produces additive effects greater than any single or dual agonist.

In the Eli Lilly Phase 2 trial (NEJM 2023), retatrutide at 12 mg/week produced approximately 24% body weight reduction at 48 weeks — the largest weight loss reported for any peptide class in clinical research to date. Tirzepatide (dual agonist) produced ~20–22% at comparable timepoints, and semaglutide (single GLP-1) ~15% at 68 weeks. All doses above 4 mg showed statistically significant weight reduction vs. placebo.

• Weight loss: ~24% body weight reduction at 48 weeks (12 mg/week dose)
• Glycemic control: significant HbA1c reductions even in non-diabetic subjects
• Visceral fat: disproportionate reduction in abdominal adiposity compared to subcutaneous fat
• Energy expenditure: glucagon component increases metabolic rate via enhanced lipolysis

Phase 3 trials are ongoing. Retatrutide is not yet FDA-approved and is currently available only in research contexts.

Retatrutide Side Effects and Safety

Retatrutide's side effect profile is consistent with the GLP-1 class, though the additional glucagon agonism may contribute to a slightly higher incidence of nausea compared to dual agonists at comparable weight-loss doses. Most GI side effects are dose-dependent and transient, peaking during the titration phase and subsiding once the body adapts.

• Nausea — most common (~40–60% during titration); improves significantly after stabilizing at a dose for 4+ weeks
• Vomiting and diarrhea — common at dose-up steps; slowing titration or pausing escalation reduces severity
• Constipation — GLP-1 slows GI motility; adequate fiber and water intake helps
• Decreased appetite — expected pharmacological effect; monitor for inadequate protein intake
• Injection site reactions — mild erythema or bruising; rotate injection sites
• Heart rate increase — mild elevation (~2–4 bpm) reported in trials; generally not clinically significant
• Gallbladder issues — rapid weight loss increases gallstone risk; report right upper quadrant pain promptly

Retatrutide is contraindicated in individuals with a personal or family history of medullary thyroid carcinoma (MTC) or multiple endocrine neoplasia syndrome type 2 (MEN2). A boxed warning for thyroid C-cell tumors applies to the GLP-1 class based on rodent data; clinical significance in humans has not been established. Always consult a licensed healthcare provider before use.

Safe Handling, Storage, and Disposal

Reconstituted retatrutide should be refrigerated at 2–8°C and used within 28 days. Never freeze reconstituted peptide — freeze-thaw cycles degrade potency. Use a fresh needle for each injection. Wipe the rubber stopper with an alcohol swab before each draw. Dispose of needles and syringes in a puncture-resistant sharps container — never in regular trash or recycling.

Unreconstituted lyophilized powder should be stored frozen at −20°C for long-term storage. If you receive retatrutide without cold packs and it has reached room temperature for an extended period, potency may have been compromised.