Research library

Retatrutide

LY3437943 · Reta · Triple-G

Evidence B · Some human evidenceNot approved for human use

In one line. A strong weight loss result in human trials, but still an unapproved, investigational medicine.

What it is

Retatrutide is a man-made peptide that acts on three hormone targets at once: GLP-1, GIP and glucagon. It is injected under the skin once a week. It is still being tested and is not an approved medicine.

What is actually known

Phase 2 human trials showed large weight loss and less liver fat. The highest dose tested was 12 mg a week. Larger trials are running.

At a glance

RouteUnder the skin

How oftenOnce a week

Half-lifeabout 6 days

PeakNot established in humans

Mix withBacteriostatic water

After mixingRefrigerate 2-8 C, use within 28 days

Dose schedule

Clinical trial

Source: Jastreboff AM et al., N Engl J Med 2023 (phase 2), escalation used for the 12 mg group

Weeks	Dose	How often
1 to 4	2 mg	Once a week
5 to 8	4 mg	Once a week
9 to 12	8 mg	Once a week
13 onwards	12 mg	Once a week

The trial raised the dose every 4 weeks up to 12 mg. Lower groups stopped at 4 or 8 mg. No dose above 12 mg was tested in this trial.

Mixing and drawing up

Pick your vial size. Water is chosen so every step reads between 2 and 100 units on a U-100 insulin syringe. Every number below is calculated, not typed.

Vial5 mg

Add water1 mL

Strength5 mg/mL

1 unit50 mcg

Dose	Draw	Units	Doses in vial	Used within 28 days
2 mg	0.4 mL	40 U	2	2
4 mg	0.8 mL	80 U	1	1
8 mg				Not from this vial: more than the vial holds
12 mg				Not from this vial: more than the vial holds

Vial10 mg

Add water1 mL

Strength10 mg/mL

1 unit100 mcg

Dose	Draw	Units	Doses in vial	Used within 28 days
2 mg	0.2 mL	20 U	5	4 (1 left over: choose a smaller vial)
4 mg	0.4 mL	40 U	2	2
8 mg	0.8 mL	80 U	1	1
12 mg				Not from this vial: more than the vial holds

Vial15 mg

Add water1 mL

Strength15 mg/mL

1 unit150 mcg

Dose	Draw	Units	Doses in vial	Used within 28 days
2 mg	0.133 mL	13.3 U	7	4 (3 left over: choose a smaller vial)
4 mg	0.267 mL	26.7 U	3	3
8 mg	0.533 mL	53.3 U	1	1
12 mg	0.8 mL	80 U	1	1

Vial20 mg

Add water1 mL

Strength20 mg/mL

1 unit200 mcg

Dose	Draw	Units	Doses in vial	Used within 28 days
2 mg	0.1 mL	10 U	10	4 (6 left over: choose a smaller vial)
4 mg	0.2 mL	20 U	5	4 (1 left over: choose a smaller vial)
8 mg	0.4 mL	40 U	2	2
12 mg	0.6 mL	60 U	1	1

Vial30 mg

Add water1.5 mL

Strength20 mg/mL

1 unit200 mcg

Dose	Draw	Units	Doses in vial	Used within 28 days
2 mg	0.1 mL	10 U	15	4 (11 left over: choose a smaller vial)
4 mg	0.2 mL	20 U	7	4 (3 left over: choose a smaller vial)
8 mg	0.4 mL	40 U	3	3
12 mg	0.6 mL	60 U	2	2

Vial40 mg

Add water2 mL

Strength20 mg/mL

1 unit200 mcg

Dose	Draw	Units	Doses in vial	Used within 28 days
2 mg	0.1 mL	10 U	20	4 (16 left over: choose a smaller vial)
4 mg	0.2 mL	20 U	10	4 (6 left over: choose a smaller vial)
8 mg	0.4 mL	40 U	5	4 (1 left over: choose a smaller vial)
12 mg	0.6 mL	60 U	3	3

Vial50 mg

Add water2.5 mL

Strength20 mg/mL

1 unit200 mcg

Dose	Draw	Units	Doses in vial	Used within 28 days
2 mg	0.1 mL	10 U	25	4 (21 left over: choose a smaller vial)
4 mg	0.2 mL	20 U	12	4 (8 left over: choose a smaller vial)
8 mg	0.4 mL	40 U	6	4 (2 left over: choose a smaller vial)
12 mg	0.6 mL	60 U	4	4

Vial60 mg

Add water3 mL

Strength20 mg/mL

1 unit200 mcg

Dose	Draw	Units	Doses in vial	Used within 28 days
2 mg	0.1 mL	10 U	30	4 (26 left over: choose a smaller vial)
4 mg	0.2 mL	20 U	15	4 (11 left over: choose a smaller vial)
8 mg	0.4 mL	40 U	7	4 (3 left over: choose a smaller vial)
12 mg	0.6 mL	60 U	5	4 (1 left over: choose a smaller vial)

Certificates, tools and where to buy

Certificates on file for Retatrutide: the laboratory's original pages.

Work out the draw · Plan a schedule · Reading a syringe · Shop

Do not use if

Not approved: use only in a registered clinical trial or under a physician who knows it is investigational
Personal or family history of medullary thyroid carcinoma or MEN 2 (a warning for this medicine class)
Pregnancy or breastfeeding
History of pancreatitis

Watch for

Nausea, vomiting, diarrhoea and constipation, mostly after a dose increase
A faster resting heart rate, which rose with dose in the trials
Unusual skin sensitivity or tingling, reported more often than on placebo
Gallbladder problems and dehydration, as with other medicines in this class

Stop and get medical help if

Severe stomach pain that may go through to the back
Pain under the right ribs, fever, yellow eyes or skin
A racing or irregular heartbeat
Unable to keep fluids down

Interactions

Do not combine with tirzepatide, semaglutide or other GLP-1 medicines
Insulin or sulfonylureas: risk of low blood sugar

A good vial

White to off-white dry cake
Clear, colourless solution after gentle swirling

Do not use the vial if

Cloudy or particles after mixing
Yellow or brown colour
Collapsed or melted cake

Combinations

With	Status	Why, and on what basis
Tirzepatide	Avoid	Overlapping drug class; more side effects, no evidence of added benefit (class pharmacology)

Evidence

Investigational medicine with published phase 2 human trials in obesity and fatty liver disease. Phase 3 results are announced but not all published. Not approved anywhere.

DOI:10.1056/NEJMoa2301972 Jastreboff AM et al. N Engl J Med 2023: phase 2 obesity trial, 338 adults, 48 weeks. Mean weight change up to -24.2% at 12 mg vs -2.1% placebo.
DOI:10.1038/s41591-024-03018-2 Sanyal AJ et al. Nat Med 2024: liver fat fell about 82% at 8 to 12 mg at 24 weeks.
NCT05929066 TRIUMPH-1 phase 3 obesity trial (registry).

This page is research and education. It is not medical advice and not a personal dosing plan. Doses marked "Product label" come from the official prescribing information; doses marked "Market practice" show what is used in this market and are not a recommendation. Use prescription medicines only under the care of a licensed physician.