Retatrutide Starting Dose: The First-Timer Protocol
The standard retatrutide starting dose is 2mg subcutaneously, once weekly, held for 4 weeks before titration. Some users start lower at 1mg. Here is what week 1 actually looks like, how to set up your first injection, and when to move up.
The Standard Starting Dose
2mg weekly. That is the number to remember. It comes directly from the TRIUMPH Phase 3 program, where Eli Lilly used 2mg as the lowest escalation tier across all dose cohorts. Even the 12mg maintenance arm starts at 2mg and titrates up. There is no published TRIUMPH cohort that started at 4mg or higher.
Sensitive users — those who had to abandon semaglutide or tirzepatide because of nausea — often start at 1mg weekly for the first two weeks, then bridge to 2mg. This is a research-peptide community pattern, not a Lilly protocol, but it has been the most-discussed tolerability hack on the retatrutide Reddit threads since mid-2024.
Why Not Start Higher?
Retatrutide activates three receptors simultaneously: GLP-1 (appetite suppression), GIP (insulin response), and glucagon (energy expenditure). The glucagon arm is the wild card. It increases resting heart rate, can raise fasting glucose temporarily, and adds a layer of fatigue that semaglutide and tirzepatide users have not experienced before. Starting at 4mg or higher loads all three pathways at once with no tolerance built — about 30% of users in early Phase 2 studies dropped out for tolerability when started above 4mg.
For background on why this matters, see our retatrutide mechanism of action guide.
Reconstitution Math for a 2mg Dose
Most research-grade retatrutide ships as a 10mg lyophilized vial. To get 2mg per injection:
- Add 2mL bacteriostatic water to the 10mg vial
- Concentration: 5mg per mL (or 50 units of drug per 100 units of solution on a U-100 syringe)
- 2mg dose = 0.4mL = 40 units on a U-100 insulin syringe
- 1mg dose = 0.2mL = 20 units
If your vial is 15mg, add 3mL for the same 5mg/mL concentration. If it is 5mg, add 1mL. Keep the math at 5mg/mL — it produces clean integer unit counts that are hard to misread.
Use our peptide reconstitution calculator if your vial size is non-standard. For step-by-step injection technique, see how to inject peptides.
Week 1 Timeline
Day 1 (injection day): Inject morning, after a light meal. Drink water through the day. Expect mild nausea 6-12 hours post-injection.
Day 2-3: Peak nausea. Most users describe it as "motion sickness lite" rather than acute. Small meals every 3-4 hours keep it manageable. Skip greasy or heavy protein meals.
Day 4-5: Nausea fades. Fatigue often replaces it. Appetite suppression starts becoming noticeable — users report feeling full after half-portions.
Day 6-7: Most side effects resolved. Some users feel completely normal by day 7, others have residual mild fatigue. This is when to plan your next injection.
When to Escalate
After four 2mg doses, if you have had:
- No vomiting in the past two weeks
- Nausea rated 3/10 or lower
- Normal energy levels by day 4 post-injection
- Bowel function near baseline
Then move to 4mg weekly. If any of these are still problems, hold 2mg for another 2-4 weeks before attempting the increase. The retatrutide dosing schedule covers the full titration ladder from 2mg through 12mg maintenance.
If You Are Switching From Tirzepatide or Semaglutide
Stop your current GLP-1 for 7 days, then inject 2mg retatrutide. Do not start retatrutide at a higher dose just because you tolerated tirzepatide 10mg or semaglutide 2.4mg. The glucagon receptor activation is novel and your tolerance to GIP/GLP-1 dual agonism does not transfer.
For users on tirzepatide 10mg+, some clinicians shorten the washout to 5 days. The argument: tirzepatide half-life is ~5 days, so 5 days is one half-life. Anecdotally this works but produces stronger overlap nausea in the first 48 hours.
Detailed switching protocols in our how to get retatrutide guide.
Common Starting Dose Mistakes
1. Starting at 4mg because Reddit said so. Some users post about starting at 4mg without issues. Survivorship bias — the users who tolerated it post, the ones who quit do not. Stick with 2mg.
2. Skipping weeks 2-4. One injection at 2mg, then jumping to 4mg the next week. The starting dose only works if you complete the four-week tolerance build. Single doses do not develop tolerance.
3. Drinking heavily during week 1. Alcohol amplifies retatrutide nausea and the glucagon effects on hepatic glucose. See our retatrutide and alcohol guide for the actual interaction.
4. Injecting in the same spot. Rotate between abdomen, thigh, and upper arm. Same-site injections build local fat atrophy and reduce absorption over time.
5. Using expired or improperly stored bac water. Bac water past 28 days post-puncture loses preservative effectiveness. New 30mL vial for every reconstitution batch.
Cost of the Starting Dose Period
At 2mg weekly for four weeks, you use 8mg total. A 10mg vial covers the entire starting period with 2mg left over for week 5. Research-grade retatrutide pricing runs $180-$280 per 10mg vial as of June 2026, so the starting month costs roughly $200-$300. Compare to full retatrutide cost breakdowns for ongoing dose tiers.
A Note on FDA Status
Retatrutide is not FDA approved as of June 2026. Eli Lilly has not yet filed an NDA, and projected commercial launch is 2027-2028. All access today is through research peptide vendors or off-label clinical trial enrollment. See retatrutide FDA approval status for the current regulatory timeline.
Frequently Asked Questions About Retatrutide
Most users start at 2mg weekly subcutaneous, mirroring the lowest TRIUMPH Phase 3 starting cohort. Some research-peptide users begin even lower at 1mg weekly to test tolerance, but Eli Lilly's trial protocols use 2mg as the floor for the first four weeks before titrating. The exception is sensitive users who experienced severe nausea on prior GLP-1 medications — they often start at 1mg weekly for two weeks, then move to 2mg.
Four weeks is the standard. TRIUMPH-1 used a 2mg starting dose for weeks 1-4, then escalated to 4mg for weeks 5-8. Holding for four weeks lets GI side effects plateau before adding more agonist activity. If nausea, fatigue, or constipation are still significant at the end of week 4, hold the starting dose for another 2-4 weeks before escalating.
No, even if you are currently on tirzepatide. Retatrutide adds glucagon receptor activation that tirzepatide lacks, and the glucagon pathway produces side effects (nausea, fatigue, increased heart rate) that titration does not predict from your tirzepatide tolerance. Cross-titrate by stopping tirzepatide for one week, then starting retatrutide at 2mg. Some clinicians shorten the gap to 5 days for users on tirzepatide 10mg or higher.
Morning is the most common choice because it lets you observe side effects during waking hours. If nausea hits, you are awake to treat it (small meals, ginger, ondansetron if prescribed). Evening dosing is fine for users who tolerate GLP-1s well or want to sleep through early symptoms, but is risky for first-timers who do not know their reaction profile yet.
Add 2mL bacteriostatic water to a 10mg vial. That produces 5mg per mL. A 2mg dose is 0.4mL — 40 units on a U-100 insulin syringe. Use the same syringe size (typically 0.5mL U-100) you would for semaglutide or tirzepatide. Our retatrutide dosage calculator handles other vial concentrations.
The most common week-1 side effects are mild nausea (40-60% of users), fatigue (30-40%), constipation or diarrhea (20-30%), and injection site soreness (10-20%). Nausea typically peaks 24-48 hours post-injection and fades by day 4-5. Fatigue can persist the full week at the starting dose but usually improves by week 3. Heart rate may increase 5-10 bpm — this is the glucagon pathway, not a problem, but worth tracking.
After. Inject on an empty stomach or several hours after a small meal. Heavy meals immediately before injecting often trigger worse nausea because the drug peaks in plasma at 6-12 hours and finds an already-distended stomach. Many users report best tolerance with a light breakfast 2-3 hours before injection, then a small dinner.
Some users split 2mg into two 1mg doses spaced 3-4 days apart to reduce peak nausea. The half-life of retatrutide is ~6 days, so splitting smooths the plasma curve. This is off-protocol — TRIUMPH used once-weekly — but it is a common research-peptide community practice for nausea-sensitive users. There is no published efficacy data on split dosing, only anecdotal tolerability reports.
Drop to 1mg weekly for 2-4 weeks, then attempt 2mg again. If 1mg is still intolerable, retatrutide may not be the right molecule for you — the triple agonism is uniquely strong and a small percentage of users cannot tolerate it at any dose. Consider tirzepatide or semaglutide as alternatives.
Negligible. At 2mg weekly for four weeks, most users lose 2-5 pounds — mostly water from reduced food intake, not fat. Real fat loss kicks in at 4mg and accelerates at 8mg. The starting dose exists to build tolerance, not to drive weight loss. Setting that expectation prevents the disappointment cycle that pushes users to escalate too fast.