The world's first triple-action weight loss peptide that simultaneously activates three hormone receptors—GIP, GLP-1, and glucagon—delivering unprecedented weight loss results of up to 24% body weight in clinical trials [1][2].
Written by Michael Carroll — Owner, Director of Research · Reviewed by the Peptide Initiative Research Team · Editorial standards
Subcutaneous
Route
3 recommended
Sites
Once weekly
Frequency
Preparation
Pre-filled pen or vial of retatrutide (as supplied)
Insulin syringes (29-31 gauge) if using vials
Alcohol swabs for injection site cleaning
Sharps disposal container
Pro tip
Prepare all supplies on a clean surface before you begin. Having everything ready makes the process smoother and more sterile.
Mixing
Example calculation
Most clinical trials used pre-filled delivery systems. If using research vials, typical concentration allows direct withdrawal of the prescribed dose. Example: 5mg/mL concentration—for a 4mg dose, draw 0.8mL.
Dose calculation
For research purposes with a 5mg/mL solution: 1mg dose = 0.2mL (20 units on insulin syringe), 4mg dose = 0.8mL (80 units), 8mg dose = 1.6mL (may require two injections), 12mg dose = 2.4mL (multiple injection sites needed).
Location
Site 01
Abdomen
Pinch the skin 2 inches from navel. Avoid the area directly around the belly button. Rotate between left and right sides.
Site 02
Outer Thigh
Middle third of the outer thigh. Keep at least 4 inches above the knee and below the hip. Alternate legs each injection.
Site 03
Upper Arm
Back or outer area of the upper arm. This site may require assistance from another person for proper technique.
Rotate between 3 sites to prevent tissue buildup and ensure consistent absorption.
Pro tip
Rotate your injection sites with each dose to prevent lipohypertrophy (buildup of fatty tissue). Keep a simple log of where you last injected.
Step by step
Wash hands thoroughly with soap and water
Clean the injection site with an alcohol swab and let it dry completely
Pinch a fold of skin at the injection site
Insert the needle at a 45-90 degree angle (90 degrees if you have adequate subcutaneous tissue)
Inject the medication slowly over 5-10 seconds
Remove the needle and apply gentle pressure—don't rub
Pro tip
This peptide uses subcutaneous injection (just under the skin)—the same easy technique used for insulin. Inject at a 45-90 degree angle into pinched skin. Aspirate before injecting to ensure you haven't hit a blood vessel.
Timing
Optimal timing
Best time
Pick any consistent day each week—what matters most is doing it the same day each week. Many people choose weekend mornings so any initial nausea happens when they can rest.
With food?
Inject regardless of food timing. However, eating slowly and avoiding large, fatty meals helps minimize nausea. Many users find eating smaller, more frequent meals works better on this medication.
Stacking notes
Do not combine with other GLP-1 agonists like semaglutide or tirzepatide—retatrutide already hits all three receptors [2]. Metformin is safe and often beneficial to continue [6].
Sample daily schedule
Same day each week (e.g., Saturday morning)
As prescribed: 1-12 mg based on titration phase injection
Site: Rotate between abdomen, thigh, and arm weekly
Once-weekly dosing. Pick a day you'll remember consistently. If you miss a dose, take it within 4 days of the missed dose. If more than 4 days have passed, skip that week and resume on your normal schedule.
Dosing tiers
Dose
2 mg
Frequency
Once weekly
Duration
Weeks 1-4 (then escalate 2 mg every 4 weeks)
Phase 2 obesity trial initiated higher-dose arms at 2 mg weekly with stepwise 2 mg increases every 4 weeks to limit GI effects [1].
Dose
4-8 mg
Frequency
Once weekly
Duration
Maintenance after titration
Mid-range maintenance doses; 8 mg produced ~22% mean weight loss at 48 weeks in the phase 2 trial [1][3].
Dose
12 mg
Frequency
Once weekly
Duration
Maintenance (highest studied)
Highest studied dose; produced ~24% mean weight reduction at 48 weeks [1]. Still investigational (not FDA-approved).
Preservation
Before mixing
Keep retatrutide refrigerated at 36-46°F (2-8°C). Protect from light by keeping in original packaging. Never freeze the medication. Can tolerate brief periods at room temperature (up to 86°F/30°C) for transport.
After mixing
Once prepared for use, store refrigerated at 36-46°F (2-8°C). Do not freeze reconstituted solution. Keep away from direct light. Use within 28 days of first use.
Shelf life after mixing
28 days
Signs of degradation
Discard the vial immediately if you notice any of these:
Cloudy or discolored solution (should be clear and colorless)
Visible particles or clumps floating in the solution
Solution has been frozen
Past expiration date or more than 28 days since opening
Important
When to stop
Severe or persistent abdominal pain (possible pancreatitis)—seek emergency care
Signs of allergic reaction: rash, swelling, difficulty breathing
Persistent severe nausea or vomiting that doesn't improve with dose reduction
Symptoms of gallbladder problems (right upper abdominal pain)
Symptoms of severe hypoglycemia that recur despite medication adjustments
Any concerning mental health changes
Retatrutide is an investigational medication currently in clinical trials. It is not FDA approved. Any use should be under the supervision of a qualified healthcare provider. Never start, stop, or change your dose without medical guidance.
Clean technique checklist
Wash hands thoroughly with soap and water before handling supplies
Swab vial tops and injection site with alcohol and let dry
Never touch the needle tip or allow it to contact non-sterile surfaces
Use a new syringe and needle for each injection
Dispose of used sharps in a proper sharps container
Store reconstituted peptides according to the storage instructions above
Published research
Jastreboff AM, Kaplan LM, Frías JP et al. · 2023
In 338 adults with obesity, retatrutide produced dose-dependent weight loss up to 24.2% at 48 weeks with the 12mg dose—the highest ever recorded for any anti-obesity medication in a Phase 2 trial. Even the lowest dose (1mg) outperformed placebo.
Kaur M, Misra S · 2024
This comprehensive review confirmed retatrutide's unique triple-receptor mechanism offers advantages over single or dual agonists. The glucagon receptor activation may contribute additional energy expenditure and fat burning not seen with GLP-1-only drugs.
Tewari J, Qidwai KA, Tewari A et al. · 2025
Pooled analysis of all available trials confirmed retatrutide shows a clear dose-response relationship for weight loss. The safety profile was comparable to placebo for serious adverse events, with GI symptoms being the main tolerability concern.
Coskun T, Wu Q, Schloot NC et al. · 2025
Detailed body composition analysis showed retatrutide users lost primarily fat mass while preserving lean muscle mass better than typically seen with dieting alone—crucial for long-term metabolic health.
Goldney J, Hamza M, Surti F · 2025
This review placed retatrutide in context of the obesity medication landscape, noting its triple mechanism represents a new frontier in metabolic pharmacotherapy with potential to address multiple aspects of metabolic disease simultaneously.
Rosenstock J, Frias J, Jastreboff AM et al. · 2023
In 281 adults with type 2 diabetes treated with diet and exercise alone or a stable dose of metformin, retatrutide reduced HbA1c by up to 2.02% at 24 weeks and body weight by up to 16.94% at 36 weeks. Mild-to-moderate GI adverse events occurred in 35% of retatrutide-treated participants, with no reports of severe hypoglycemia.
Sanyal AJ, Kaplan LM, Frias JP et al. · 2024
In a 98-participant substudy of adults with MASLD and at least 10% liver fat, retatrutide reduced liver fat by 81.4% (8 mg) and 82.4% (12 mg) relative to baseline at 24 weeks versus a 0.3% increase with placebo. Most participants on the two highest doses reached normal liver fat (under 5%) by 24 weeks.
Sodhi M, Rezaeianzadeh R, Kezouh A et al. · 2023
In a cohort study of patients using GLP-1 receptor agonists (liraglutide or semaglutide) for weight loss, GLP-1 agonist use was associated with increased risk of pancreatitis (adjusted hazard ratio 9.1), bowel obstruction (4.2), and gastroparesis (3.7) compared with bupropion-naltrexone users.
Liddle RA, Goldstein RB, Saxton J · 1989
Among 51 obese subjects on an 8-week very-low-calorie diet, 25.5% developed gallstones on ultrasound versus none in the non-dieting comparison group, and three required gallbladder removal—establishing rapid weight loss as a risk factor for gallstone formation.
Jastreboff AM, Aronne LJ, Ahmad NN et al. · 2022
In the SURMOUNT-1 trial of 2,539 adults with obesity, tirzepatide 15 mg produced a mean weight reduction of 20.9% at 72 weeks versus 3.1% with placebo, and 57% of participants on the highest dose lost at least 20% of body weight.
Giblin K, Kaplan LM, Somers VK et al. · 2025
Describes the TRIUMPH program: four Phase 3, multicenter, randomized, double-blind registrational trials of once-weekly retatrutide enrolling more than 5,800 participants with obesity and related conditions, confirming retatrutide is in active Phase 3 development.
Wilding JPH, Batterham RL, Davies M et al. · 2022
One year after stopping semaglutide 2.4 mg and lifestyle intervention, participants had regained two-thirds of the weight they lost during treatment (11.6 of 17.3 percentage points), and cardiometabolic improvements reverted toward baseline.
Bjerre Knudsen L, Madsen LW, Andersen S et al. · 2010
GLP-1 receptor agonists caused calcitonin release, C-cell proliferation, and C-cell tumors in rodents, but thyroid C-cells in humans and monkeys have low GLP-1 receptor expression, monkeys showed no calcitonin response to prolonged treatment, and calcitonin levels in patients on liraglutide for 2 years remained at the lower end of the normal range.
Wilding JPH, Batterham RL, Calanna S et al. · 2021
In the STEP 1 trial of 1,961 adults with overweight or obesity, once-weekly semaglutide 2.4 mg produced a mean weight loss of 14.9% at 68 weeks versus 2.4% with placebo.
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