Dosing
How muchdo I take?
Subcutaneous: A small injection into the fatty layer just under the skin the same way insulin is given.
Bioavailability High most of the dose reaches your bloodstream, just more gradually than an IV.
Starting 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].
Standard Dose
4-8 mg
Maintenance after titration
Mid-range maintenance doses; 8 mg produced ~22% mean weight loss at 48 weeks in the phase 2 trial [1][3].
Advanced Dose
12 mg
Maintenance (highest studied)
Highest studied dose; produced ~24% mean weight reduction at 48 weeks [1][2]. Still investigational (not FDA-approved).
Timing
Best time to take
Pick any consistent day each weekwhat 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.
If stacking
Do not combine with other GLP-1 agonists like semaglutide or tirzepatideretatrutide already hits all three receptors. Metformin is safe and often beneficial to continue.
Adjusting Your Dose
Increase if
+You've been on current dose for 4+ weeks with good tolerance
+Weight loss has plateaued and you're below target
+GI side effects have resolved or become minimal
+Your healthcare provider recommends escalation
Decrease if
-Nausea or vomiting is persistent and interfering with daily life
-You're losing weight too rapidly (more than 3 lbs/week consistently)
-GI side effects don't improve after 2-3 weeks on current dose
-You experience hypoglycemia symptoms
Signs of right dose
✓Steady weight loss of 1-2 lbs per week
✓Reduced appetite without severe nausea
✓Improved energy levels
✓Blood sugar levels stabilizing (if diabetic)
Dosing Calculator
Calculate Your Exact Dose
Step 1: Peptide Weight
Find the weight printed on your peptide vial label
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The peptide weight is printed on the label
The weight is on the label
Select Weight
Look for a number followed by 'mg' on the vial label (e.g., 5mg, 10mg)
Administration
How do Iuse it?
Reconstitution
What you need
•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
Example
Most clinical trials used pre-filled delivery systems. If using research vials, typical concentration allows direct withdrawal of the prescribed dose. Example: 5mg/mL concentrationfor a 4mg dose, draw 0.8mL.
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).
Injection
Route
Subcutaneous injection (just under the skin)the same easy technique used for insulin
Best sites
•Abdomen (at least 2 inches away from belly button)
•Front of thighs (middle area)
•Back of upper arms (have someone help if needed)
Technique
1.Wash hands thoroughly with soap and water
2.Clean the injection site with an alcohol swab and let it dry completely
3.Pinch a fold of skin at the injection site
4.Insert the needle at a 45-90 degree angle (90 degrees if you have adequate subcutaneous tissue)
5.Inject the medication slowly over 5-10 seconds
6.Remove the needle and apply gentle pressuredon't rub
Storage
Before reconstitution
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 reconstitution
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.
Signs of degradation
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
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.
Safety
Is itsafe?
Safety Profile
Retatrutide has shown a generally favorable safety profile in Phase 1 and Phase 2 clinical trials involving over 600 participants. Most side effects are gastrointestinal and tend to improve over time. The medication appears well-tolerated when doses are increased gradually. No major safety signals have emerged, but larger Phase 3 trials are still ongoing.
Current safety data comes from Phase 1 and Phase 2 trials conducted by Eli Lilly. Multiple Phase 3 trials are currently underway to establish long-term safety in larger populations. As a research compound not yet FDA approved, the full safety profile is still being established.
Common Side Effects
Experienced by some users
Nausea
The most frequently reported side effect, especially during dose escalation. Your gut has lots of GLP-1 receptors, and they need time to adjust.
Management: Start with lower doses and increase gradually. Eat smaller meals, avoid fatty foods, and stay hydrated. Usually improves significantly after the first few weeks.
Diarrhea
Common in the first weeks of treatment as your digestive system adapts to the medication's effects on gut motility.
Management: Stay well hydrated. Avoid greasy, spicy, or high-fiber foods initially. Usually resolves within 2-4 weeks as your body adjusts.
Constipation
Some users experience the oppositeslowed digestion can lead to constipation, especially at higher doses.
Management: Increase water intake significantly. Add fiber gradually. Gentle physical activity helps. Over-the-counter remedies are safe if needed.
Decreased appetite
This is actually the intended effect! But it can feel strange at first when you realize you're simply not hungry.
Management: This is generally positive but ensure you're still eating nutritious foods. Don't skip meals entirelyaim for smaller, protein-rich meals.
Less Common
•Increased heart rate
•Injection site reactions
These typically resolve with continued use or dose adjustment.
Stop and Seek Help If
×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.
Interactions
With other peptides
!Do NOT combine. Both target the GLP-1 receptorusing them together provides no additional benefit and increases side effects.
!Do NOT combine. Retatrutide already hits both GIP and GLP-1 receptors that tirzepatide targets, plus glucagon.
✓Limited interaction data. Theoretically safe as they work through different mechanisms, but use caution.
✓No direct interaction known. Some users stack for body composition, but data is limited.
With medications
!Insulin - High interaction risk. Retatrutide dramatically lowers blood sugarinsulin doses typically need significant reduction (20-50%) to prevent hypoglycemia.
!Sulfonylureas (glipizide, glyburide) - Increased hypoglycemia risk. These drugs also stimulate insulin release. Dose reduction usually needed.
✓Metformin - Safe and often beneficial combination. Metformin works through different mechanisms and complements retatrutide well.
✓SGLT2 inhibitors (empagliflozin, dapagliflozin) - Generally safe combination used in clinical trials. Both promote weight loss through different mechanisms.
✓Oral contraceptives - Slowed GI transit may affect absorption. Consider using backup contraception or switch to non-oral methods.
✓Levothyroxine - Take thyroid medication at least 30-60 minutes before retatrutide or 4 hours after. GI slowing may affect absorption.
With supplements
✓Vitamin B12 - GLP-1 agonists may reduce B12 absorption over time. Consider supplementation, especially long-term.
✓Protein supplements - Safe and often helpful to maintain adequate protein intake while eating less overall.
✓Fiber supplements - Safe but start slowly. Can help with constipation but may worsen early GI symptoms if added too quickly.
✓Multivitamins - Safe and recommended. When eating less food, ensuring micronutrient adequacy is important.
Want the Full Picture?
View the complete Retatrutide research profile including mechanism of action, clinical studies, effectiveness timeline, and FAQ.