Retatrutide Guide Last updated: May 23, 2026 Reading time: 10 min Reviewed for accuracy by the Bio Apex protocols team

Retatrutide dosage calculator & titration guide

Q: What is the standard Retatrutide dose?

Retatrutide is dosed by titration. The standard schedule starts at 2 mg once weekly for weeks 1-4, then increases by 2 mg every 4 weeks: 4 mg (weeks 5-8), 6 mg (weeks 9-12), 8 mg (weeks 13-16), then maintenance at 8-12 mg once weekly. Maximum studied dose is 12 mg per week.

Q: How do I reconstitute Retatrutide?

Wipe both vial stoppers with alcohol, draw the calculated volume of bacteriostatic water with a 3 mL mixing syringe, slowly inject the water down the inside wall of the Retatrutide vial (not onto the powder), swirl gently for 20-30 seconds until fully dissolved, inspect that the solution is clear and colorless, then label with the date and refrigerate at 2-8 degrees Celsius. The most common ratio is 2 mL of bacteriostatic water per 10 mg vial.

Q: How much bacteriostatic water do I add to a Retatrutide vial?

For a 10 mg vial, 2 mL of bacteriostatic water gives 5 mg/mL concentration - a 2 mg dose draws 40 units on a 1 mL insulin syringe. For higher doses (8-12 mg per week), use a more concentrated mix: 10 mg in 1 mL water (10 mg/mL) keeps a 10 mg dose within a single 1 mL syringe. For a 20 mg vial, 2 mL or 4 mL of water are common.

Q: What is the maximum Retatrutide dose?

The maximum studied dose in Phase 2 clinical research was 12 mg once weekly. Doses above this have not been tested. Maintenance doses of 8 mg or 10 mg are commonly used by people who don't tolerate the 12 mg dose due to GI side effects.

Q: How is Retatrutide different from Tirzepatide?

Retatrutide is a triple receptor agonist activating GLP-1, GIP, and glucagon receptors. Tirzepatide is a dual agonist activating only GLP-1 and GIP. The glucagon receptor activation in Retatrutide adds direct energy expenditure increase. In Phase 2 trials Retatrutide produced approximately 24% body weight reduction at 48 weeks at 12 mg, compared to approximately 21% for Tirzepatide.

TL;DR

Retatrutide is a once-weekly triple agonist (GLP-1, GIP, glucagon) dosed by titration: start at 2 mg/week and increase by 2 mg every 4 weeks up to a maintenance dose of 8–12 mg/week. For a 10 mg vial reconstituted with 2 mL of bacteriostatic water (5 mg/mL), a 2 mg dose draws 40 units on a 1 mL insulin syringe.

Quick math: mg ÷ mL = concentration. Weekly mg ÷ concentration = mL per injection. mL × 100 = insulin units.

Retatrutide · Triple agonist

Retatrutide Dosage Calculator

Pre-configured for Retatrutide. Weekly dosing with built-in titration schedule.

Titration schedule

Tap the week of your protocol

Reconstitution

Retatrutide in vial

Bacteriostatic water added

Weekly dose

Desired dose (per week)

Split into Syringe size

Results

Heads up:

Concentration 5 mg/mL 5,000 mcg/mL

Draw per injection 40 units 0.4 mL · 2 mg

Weekly total 2 mg / week 1 injection · 2 mg

Vial lasts 5 weeks 5 injections · 10 mg total

Note: Retatrutide is a once-weekly subcutaneous peptide. Stable at 2–8°C for ~30 days reconstituted. Most protocols titrate slowly to minimize GI side effects.

Retatrutide quick reference

Mechanism Triple agonistGLP-1, GIP, glucagon

Typical dose range 2–12 mgper week, titrated up

Frequency Once weeklysame day each week

Titration +2 mg / 4 wksslow ramp reduces GI sides

Half-life ~6 dayssteady state ~4 weeks

Injection site Subcutaneousabdomen, thigh, upper arm

Stability after mixing ~30 daysrefrigerated, 2–8°C

Common vial sizes 5 / 10 / 15 / 20 mg30 mg multi-dose available

What is Retatrutide?

Retatrutide (LY-3437943) is a synthetic peptide developed as a triple receptor agonist — it simultaneously activates GLP-1, GIP, and glucagon receptors. This three-receptor activation differentiates it from the two-receptor mechanism of Tirzepatide (GLP-1 + GIP) and the single-receptor mechanism of Semaglutide (GLP-1 only).

In Phase 2 clinical research it produced the largest weight reductions of any incretin-class peptide reported to date — around 24% mean body weight reduction at 48 weeks at the 12 mg/week dose, with no observed plateau through the trial duration.

What is the standard Retatrutide dose?

Retatrutide is titrated — meaning the dose is increased gradually over several months rather than starting at the target dose. The standard titration schedule starts at 2 mg/week and increases by 2 mg every 4 weeks until reaching a maintenance dose between 8 and 12 mg/week.

Week 1–4 2 mg once weekly

Week 5–8 4 mg once weekly

Week 9–12 6 mg once weekly

Week 13–16 8 mg once weekly

Maintenance 10 mg once weekly

Maximum 12 mg once weekly

Why titrate? The triple receptor activation produces strong GI side effects (nausea, vomiting, diarrhea) when started high. A 4-week step-up at each dose level gives the body time to adapt and dramatically reduces dropout rates in clinical research.

How do I reconstitute Retatrutide?

Retatrutide ships as a lyophilized (freeze-dried) white powder. You mix it with bacteriostatic water (0.9% benzyl alcohol) before use. Because Retatrutide doses are in milligrams (not micrograms like most research peptides), draw volumes are larger — typically 0.2–1.2 mL per injection.

Sanitize both vial stoppers with alcohol
Use a fresh 70% isopropyl prep pad on the rubber septum of both the Retatrutide vial and the bacteriostatic water vial. Air-dry 10 seconds.
Draw your bacteriostatic water
Use a 3 mL syringe with a drawing needle to pull the calculated volume. 2 mL per 10 mg vial is the most popular ratio (5 mg/mL concentration).
Inject down the inside wall of the vial
Angle the needle so water trickles down the glass — not directly onto the powder. Direct stream causes foaming.
Swirl gently — never shake
Roll the vial between your palms for 20–30 seconds until fully dissolved. Shaking creates foam that degrades the peptide.
Inspect the solution
It should be completely clear and colorless. Any cloudiness, particles, or yellow tint means the peptide is degraded or contaminated — discard.
Label and refrigerate immediately
Write the reconstitution date and concentration on the vial. Store at 2–8°C (36–46°F). Use within 30 days.

How much bacteriostatic water do I add to a Retatrutide vial?

Because Retatrutide doses span a wide range (2 to 12 mg) and draw volumes are already larger than typical peptides, picking the right reconstitution ratio matters:

Vial	BAC water	Concentration	2 mg dose =	8 mg dose =	12 mg dose =
10 mg	1 mL	10 mg/mL	20 units	80 units	too large
10 mg	2 mL	5 mg/mL	40 units	too large	too large
15 mg	3 mL	5 mg/mL	40 units	too large	too large
20 mg	2 mL	10 mg/mL	20 units	80 units	too large
20 mg	4 mL	5 mg/mL	40 units	too large	too large
30 mg	3 mL	10 mg/mL	20 units	80 units	too large

Sweet spot: The 10 mg / 2 mL mix (5 mg/mL) is the most popular for early titration (2–4 mg/week). At higher maintenance doses (8–12 mg/week), a more concentrated 10 mg/mL mix keeps draws within a single insulin syringe.

Why some doses are "too large": A standard 1 mL insulin syringe holds 100 units (1 mL). A 12 mg dose at 5 mg/mL = 2.4 mL — more than 2× the syringe capacity. Options: increase concentration (less water), split the dose into 2 injections per week, or use a tuberculin syringe.

How do I split a Retatrutide dose if it exceeds my syringe?

High maintenance doses (10–12 mg/week) can exceed a single 1 mL syringe at common concentrations. Two practical workarounds:

More concentrated mix. A 10 mg vial in 1 mL water gives 10 mg/mL — a 10 mg dose draws 100 units (1 mL syringe full). 12 mg still won't fit, but 10 mg and below will.
Split into 2 injections per week. Inject half the weekly dose on day 1, the other half on day 4 (e.g., Sunday + Wednesday). The calculator's "split into 2 injections" option handles this automatically.

What are common Retatrutide side effects?

Retatrutide's side effect profile is similar to other incretin peptides but more pronounced due to the triple receptor activation. The vast majority are gastrointestinal and dose-dependent:

Side effect	Frequency in Phase 2	Typical management
Nausea	~40–60%	Slow titration, ginger, smaller meals
Vomiting	~25–35%	Hold dose, do not titrate up that month
Diarrhea	~20–30%	Hydration, BRAT diet, hold dose if severe
Constipation	~15–25%	Fiber, hydration, stool softener
Injection site reaction	~5–10%	Rotate injection sites weekly
Heart rate increase	~5–10 bpm	Monitor, usually transient

How long does reconstituted Retatrutide last?

Lyophilized (powder): 24 months at −20°C, 12 months refrigerated
Reconstituted (in BAC water): ~30 days refrigerated at 2–8°C
Frozen aliquots: 3–6 months at −20°C in single-use vials

Keep in the original vial or one with similar amber/opaque packaging. Don't leave the vial at room temperature for extended periods — pull from the fridge, draw your dose, return immediately.

What are the most common Retatrutide mistakes?

Titrating too fast. Jumping from 2 mg to 6 mg in week 5 dramatically increases nausea and vomiting risk. Stick to +2 mg every 4 weeks minimum.
Wrong syringe size. Using a 0.3 mL syringe for an 8 mg dose at 5 mg/mL (= 160 units, way over capacity). Use a 1 mL syringe for Retatrutide.
Forgetting to label. With multiple vial sizes and concentrations possible, a misread vial leads to a 2× dosing error.
Skipping the titration. Starting at 8 mg "to save time" produces nausea so severe most users discontinue within 2 weeks.
Mismatched dosing day. Inject the same day each week. The 6-day half-life builds steady-state levels — randomizing the day creates peaks and troughs.
Shaking the vial. Denatures the peptide. Always swirl.

Frequently asked questions about Retatrutide

What is the maximum Retatrutide dose?

The maximum dose studied in Phase 2 was 12 mg once weekly. Doses above this haven't been tested in published clinical research. Maintenance doses of 8 mg or 10 mg are commonly used by people who don't tolerate 12 mg.

How long does it take Retatrutide to work?

Appetite suppression is typically noticeable within 1–2 weeks. Measurable weight loss appears around weeks 4–6. Because Retatrutide is titrated up over 12–16 weeks, the most significant weight reduction usually starts after reaching the 6–8 mg/week dose level.

Can I skip the Retatrutide titration?

Strongly not recommended. The +2 mg per 4 weeks titration exists specifically because Phase 2 trial participants who titrated faster experienced severe nausea, vomiting, and dropout rates above 30%. The slow ramp gives the GI tract time to adapt to triple receptor activation.

How is Retatrutide different from Tirzepatide?

Retatrutide is a triple agonist (GLP-1 + GIP + glucagon). Tirzepatide is a dual agonist (GLP-1 + GIP only). The glucagon receptor activation in Retatrutide adds direct energy expenditure increase on top of the appetite suppression both share. In Phase 2 head-to-head equivalents, Retatrutide produced approximately 24% body weight reduction at 48 weeks vs ~21% for Tirzepatide.

Which day of the week should I inject Retatrutide?

Any day, but pick one and stick with it. The 6-day half-life means dosing on the same day each week produces stable, predictable blood levels. Many people pick Sunday so any peak side effects fall on a weekend. Once chosen, only shift the day if you're more than 48 hours late — otherwise inject as soon as you remember and continue the original schedule.

Can I take Retatrutide with other peptides?

Stacking with other peptides is generally avoided during Retatrutide titration because it makes side effect attribution difficult. Once on a stable maintenance dose, some users add BPC-157 for tissue healing or short cycles of growth-hormone-releasing peptides. Do not combine with other GLP-1, GIP, or glucagon agonists.

What happens if I miss a Retatrutide dose?

If the missed dose is within 48 hours of the scheduled day, inject as soon as you remember and continue your normal schedule. If more than 48 hours late, skip the missed dose and resume on the next scheduled day — never double up to "catch up." Doubling a Retatrutide dose causes severe GI side effects.