The Bottom Line
Retatrutide (commonly called “reta”) dosing follows a titration schedule starting at 2mg/week and escalating to a maximum of 12mg/week over 20+ weeks. The standard protocol increases every 4 weeks: 2mg, 4mg, 6mg, 8mg, 10mg, 12mg. Not everyone needs to reach 12mg - Phase 3 data shows significant weight loss at 8mg and 9mg as well. Many users split their weekly dose into 2-3 smaller injections to reduce nausea and smooth out blood levels. Use our free GLP-1 dose calculator to calculate exact units for any dose, and our split-dose calculator if you’re dividing your weekly dose across multiple injections.
Retatrutide Dosage at a Glance
Retatrutide is still in Phase 3 trials, so there is no FDA-approved dosage and no official schedule to follow. What exists is the dosage ladder the trials used, which is what people and their prescribers work from:
| Week | Dosage | What it is for |
|---|---|---|
| 1 to 4 | 2 mg once a week | Tolerance. Not a working dose yet |
| 5 to 8 | 4 mg once a week | First real appetite suppression |
| 9 to 12 | 6 mg once a week | Glucagon effects start showing up |
| 13 to 16 | 8 mg once a week | Where most people settle |
| 17+ | 10 to 12 mg once a week | The top of the trial range, not a target |
Everyone starts at 2 mg regardless of what they were on before, each step is held four weeks, and plenty of people stop climbing at 4 or 8 mg because that is the dosage that works for them with side effects they can live with. The highest dosage studied is 12 mg. Splitting a weekly dosage across two injections is common and does not change the weekly total.
What Dose Should You Start At?
Retatrutide (LY3437943) is a triple hormone receptor agonist that activates GLP-1, GIP, and glucagon receptors simultaneously. Due to the glucagon receptor component - which is not present in tirzepatide (“tirz”) or semaglutide - all dosing protocols start at the lowest tier regardless of prior GLP-1 experience.
The starting dose is 2mg/week for the first 4 weeks. This applies even if you are switching from tirzepatide at 15mg/week. The glucagon receptor activation introduces pharmacological effects your body has not been exposed to, and starting higher significantly increases the risk of severe nausea, vomiting, and GI distress.
There is no matching your old tirzepatide dose - the glucagon receptor means everyone starts retatrutide at 2mg regardless of prior GLP-1 experience.
Important
Retatrutide is in Phase 3 clinical trials and is not FDA-approved. The dosing information in this guide is based on published Phase 2 and Phase 3 clinical trial protocols and community experience. This is for educational purposes only. Work with a licensed healthcare provider for dosing decisions and monitoring.
What People Actually Start At
Every retatrutide dosing article online cites the same four numbers, because those are the only numbers that exist: the TRIUMPH trial arms of 1 mg, 4 mg, 8 mg and 12 mg. Retatrutide has no FDA label, so there is no approved schedule to quote.
Here is what people actually do. This is aggregated from anonymised dosing logs in the Regimen app, as of September 2026. It is a record of behaviour, not a recommendation.
| Starting dose | Share of users |
|---|---|
| 1 mg | 24.1% |
| 2 mg | 19.4% |
| 0.5 mg | 16.7% |
| 4 mg | 6.4% |
| 1.5 mg | 5.6% |
| 2.5 mg | 4.8% |
| 3 mg | 4.8% |
Two things stand out.
Most people start well below the lowest trial arm. The single most common starting dose is 1 mg, matching the trial’s lowest arm, but the next two most common are 2 mg and 0.5 mg, and roughly two thirds of people begin somewhere between 0.5 mg and 2 mg. Starting at 4 mg, the trial’s second arm, is uncommon.
And most people never get anywhere near the top of the trial range. The median highest dose anyone reaches is 2 mg. Even at the 90th percentile it is 6 mg — still below the 8 mg and 12 mg arms that produced the headline weight-loss figures. Just over half of people (55.5%) ever change their dose at all; the rest pick a number and stay there.
That gap matters when you read trial results. The 24% weight loss reported at 12 mg describes a dose most people in the real world never take.
Standard Titration Schedule (Clinical Trial Protocol)
This schedule is based on the dosing arms used in retatrutide Phase 2 and Phase 3 clinical trials. Each tier lasts a minimum of 4 weeks. See the week-by-week titration schedule in our dedicated retatrutide titration guide.
| Phase | Weeks | Dose | Purpose |
|---|---|---|---|
| Tolerance | Weeks 1-4 | 2 mg/week | Assess GI tolerance to triple-receptor activation |
| Early therapeutic | Weeks 5-8 | 4 mg/week | First meaningful appetite suppression begins |
| Intermediate | Weeks 9-12 | 6 mg/week | Glucagon effects become more noticeable - increased energy expenditure |
| Higher therapeutic | Weeks 13-16 | 8 mg/week | Significant weight loss acceleration |
| Near-maximum | Weeks 17-20 | 10 mg/week | Approaching maximum studied dose |
| Maximum | Week 21+ | 12 mg/week | Highest dose studied in Phase 2/3 trials |
Pro Tip
Not everyone needs to reach 12mg. The TRIUMPH-1 phase 3 trial (NEJM, 2024) showed the 9mg group achieved 25.9% average weight loss, only 2.4 percentage points less than the 12mg group. If you’re achieving good weight loss at 6-8mg with manageable side effects, there may be no reason to push higher. The principle is the same as with semaglutide and tirzepatide: increase only if weight loss has meaningfully stalled AND you’re tolerating the current dose well.
Community Titration Approaches
The clinical trial protocol increases dose every 4 weeks. In practice, many providers and experienced users take a different approach:
Slower Titration (5-6 Weeks Per Tier)
Staying longer at each dose - particularly at 4mg and 6mg - reduces the intensity of GI side effects. The body adapts to each dose level more completely before adding more receptor stimulation. There is no clinical penalty for titrating slowly. Your body reaches the same steady-state levels - just with fewer days of intense nausea.
The 6mg to 8mg Wall
Community reports consistently flag the jump from 6mg to 8mg as the hardest transition. This is where glucagon receptor effects intensify most noticeably - nausea, reduced appetite (sometimes to the point of difficulty eating enough), and increased body heat. Strategies for this transition:
- Split the 8mg dose into two 4mg injections (see split dosing section below)
- Stay at 6mg for 6-8 weeks instead of 4
- Increase to 7mg first (possible with compounded vials) before jumping to 8mg
Lower Maintenance Doses
Some users find their optimal dose is 6mg or 8mg and stay there long-term rather than pushing to 12mg. If you’re losing 1-2 lbs/week consistently at 8mg, increasing to 12mg adds more side effects without proportionally more weight loss. Find your effective dose and stay there.
Community Insight
A common pattern in community discussions: users who rushed to 12mg often end up reducing back to 8mg because the side effects aren’t worth the marginal extra weight loss. Users who titrated slowly and found their “sweet spot” at 6-8mg tend to stay on protocol longer with better adherence. Slower is usually better with reta.
Split Dosing and Microdosing Protocols
Split dosing means taking retatrutide twice a week instead of once, by dividing the same weekly dose in half. Instead of 8mg in one shot, you inject 4mg on Monday and 4mg on Thursday. Taking it more than once a week does not mean taking more of it: the weekly total is identical, just spread out. This approach is increasingly popular with retatrutide because the glucagon receptor activation produces a sharper nausea spike at peak blood levels than tirzepatide.
Why Split Dosing Works
- Lower peak blood levels = less nausea in the 24-48 hours after injection
- Higher trough levels = more consistent appetite suppression throughout the week
- Retatrutide’s half-life is ~6 days (144 hours), which means once-weekly dosing produces significant peaks and troughs
Common Split-Dose Protocols
| Protocol | Schedule | Example (8mg/week total) | Best For |
|---|---|---|---|
| Twice a week | Mon + Thu | 4mg + 4mg | Most popular; good balance of convenience and smoothing |
| Three times a week | Mon + Wed + Fri | 2.7mg + 2.7mg + 2.7mg | Maximum stability; lowest peaks |
| Every other day | EOD | ~2.3mg per injection | Balance of smoothing and simplicity |
How to Calculate Split Doses
- Determine your total weekly dose (e.g., 8mg)
- Divide by number of injections (8mg / 2 = 4mg per injection)
- Use the GLP-1 dose calculator to convert mg to units for your specific vial concentration
- Or use the split-dose calculator which does all of this automatically
Pro Tip
If you’re currently doing once-weekly and experiencing bad nausea days, try switching to twice-weekly at the same total dose before increasing your dose. Many users find that twice-weekly at 8mg total is more tolerable than once-weekly at 6mg - they get a higher dose with fewer side effects by smoothing the peaks.
Community Insight
The microdosing approach is especially popular among users who train regularly. By keeping blood levels more stable, they avoid the “crash day” (usually 24-36 hours post-injection) where nausea and fatigue make training difficult. With split dosing, most users report being able to train every day without a predictable bad day each week.
How to Calculate Your Dose
The formula for all reconstituted peptides:
The retatrutide reconstitution guide works this through for each vial size, and the syringe units to mL to mg guide covers the conversion itself.
Worked example:
12mg retatrutide vial + 2mL BAC water = 6.0 mg/mL
Target: 4mg/week
Units = (4 / 6.0) x 100 = 66.7 - draw 67 units
Or skip the math: GLP-1 Dose Calculator
For split dosing, just divide: 4mg split into two injections = 2mg each = 33 units per injection. Or run any vial size through our retatrutide reconstitution calculator for exact units with a draw-to-here syringe diagram.
Dose Charts by Vial Size
5mg Vial + 1mL BAC Water (5.0 mg/mL)
| Weekly Dose | Units to Draw | Weeks Per Vial |
|---|---|---|
| 2 mg | 40 units | 2.5 weeks |
| 4 mg | 80 units | 1.25 weeks |
Best for: First 4-8 weeks of titration (2-4mg doses)
12mg Vial + 2mL BAC Water (6.0 mg/mL)
| Weekly Dose | Units to Draw | Weeks Per Vial |
|---|---|---|
| 2 mg | 33 units | 6 weeks |
| 4 mg | 67 units | 3 weeks |
| 6 mg | 100 units | 2 weeks |
Best for: Titration through 2-6mg range
30mg Vial + 2mL BAC Water (15.0 mg/mL)
| Weekly Dose | Units to Draw | Weeks Per Vial |
|---|---|---|
| 4 mg | 27 units | 7.5 weeks |
| 6 mg | 40 units | 5 weeks |
| 8 mg | 53 units | 3.75 weeks |
| 10 mg | 67 units | 3 weeks |
| 12 mg | 80 units | 2.5 weeks |
Best for: Maintenance dosing at 6mg+ (finishes within 28-day stability window)
Important
Reconstituted retatrutide is stable for approximately 28 days refrigerated. Match your vial size to your current dose so you finish the vial within 4 weeks. A 30mg vial at 2mg/week would last 15 weeks on paper - but the peptide degrades well before that. Use a 5mg or 12mg vial during early titration, then switch to 30mg once you’re at 6mg+ weekly.
For detailed reconstitution instructions, see our complete Retatrutide Reconstitution Calculator Guide.
Half-Life and Injection Timing
Retatrutide has a half-life of approximately 6 days (144 hours). Key implications:
- Steady state is reached within 4-5 weeks at any given dose
- Once-weekly dosing is supported by the half-life, but produces noticeable peaks and troughs
- Best injection day/time: Most users inject in the evening so that peak nausea (usually 12-36 hours post-injection) occurs during sleep and the following day, with recovery by the second evening
- Consistency matters: Inject on the same day(s) each week at approximately the same time, moving to a fresh spot each time. Our retatrutide injection sites guide covers the four sites and a rotation you can stick to
Use our half-life visualizer to see how retatrutide blood levels change throughout the week at different dose frequencies.
When to Increase Your Dose
The long version of this decision, including the signals that say hold and how to come back down, is on when to titrate up on retatrutide. The short version:
Increase your dose only when ALL of these are true:
- You’ve been at the current dose for at least 4 weeks (preferably 5-6)
- Weight loss has stalled for 2+ weeks (less than 0.5 lbs/week)
- You’re tolerating the current dose well (nausea is minimal or gone)
- You’re eating adequate protein (1.2-1.6g/kg/day) and not over-restricting calories
- You’re not experiencing significant side effects that would worsen with a higher dose
When NOT to Increase Your Dose
Do NOT increase if:
- You’re still losing weight consistently at the current dose (even if it’s “only” 1 lb/week - that’s 52 lbs/year)
- You’re experiencing persistent nausea, vomiting, or GI issues
- Your resting heart rate has increased more than 15 bpm from baseline
- You haven’t been at the current dose for at least 4 full weeks
- You’re not eating enough (undereating + dose increase = muscle loss and metabolic adaptation)
Pro Tip
Track your weight in a 7-day moving average, not daily weigh-ins. Daily weight fluctuates 2-5 lbs based on water, sodium, and food volume. A stall is only real if the 7-day average has been flat for 2+ consecutive weeks. The Regimen app shows your moving average automatically.
Tracking Your Dosing Protocol
What to track at each dose tier:
- Dose amount and timing (especially if split dosing)
- Weight (daily or every other day for accurate moving averages)
- Side effects with severity ratings (nausea, appetite, energy, GI)
- Resting heart rate (check weekly - retatrutide can increase it 5-12 bpm)
- Protein intake (aim for 1.2-1.6g/kg - track in any food app and log in Regimen)
- Body measurements and progress photos (weight alone doesn’t capture body composition changes)
The Regimen app tracks retatrutide alongside all your other compounds with pharmacokinetic blood level modeling, so you can see exactly where your levels are throughout the week - especially useful if you’re split dosing.
What’s the best app for tracking retatrutide?
Regimen is a purpose-built tracker for retatrutide that logs each injection with dose, site rotation, and time. The free tier covers one compound, plus a 14-day trial: PK curves (half-life visualization), injection site rotation, dose reminders, and Apple Health / Health Connect correlation so you can see how retatrutide is affecting your sleep, body composition, or weight over time.
Can I track retatrutide in Apple Health?
Apple Health doesn’t have native retatrutide tracking, but apps like Regimen sync dose logs to Apple Health and pull metrics (weight, body fat, sleep) back so you can correlate medication with outcomes.
How do I track retatrutide side effects?
A tracker app with structured check-in metrics (energy, sleep, appetite, GI symptoms) is more reliable than a notes app. Regimen tracks 20+ check-in metrics that link directly to your dose log, so patterns become visible after 3 to 4 weeks.
Frequently Asked Questions
What is the standard retatrutide starting dose?
The standard starting dose is 2mg once weekly, held for a minimum of 4 weeks. This applies to everyone - including people switching from tirzepatide or semaglutide. The 2mg phase assesses tolerance to the triple-receptor mechanism, particularly the glucagon receptor which is new for anyone coming from a GLP-1 or dual-agonist compound.
Can I start retatrutide at a higher dose if I was on tirzepatide?
No. Even if you tolerated 15mg of tirzepatide, you should start retatrutide at 2mg. The glucagon receptor activation introduces pharmacological effects your body hasn’t been exposed to. Starting at a higher dose significantly increases nausea, vomiting, and GI distress risk.
Can I take retatrutide twice a week?
Some people split the weekly dose into two injections rather than one. It does not mean taking more: 8mg a week becomes 4mg on Monday and 4mg on Thursday, and the weekly total is unchanged. The reason is the peak. Retatrutide’s level tops out around 36 hours after a shot, which is when nausea is usually worst, and at steady state splitting the dose lowers that peak by roughly 15 to 20% while raising the level you sit at between shots. That is a real but modest smoothing, not a different drug. Pairs a few days apart, like Monday and Thursday, split the week evenly. No trial has tested split retatrutide dosing, so talk to your prescriber before changing your schedule.
Is split dosing better than once weekly?
For tolerability, often yes. Splitting your dose into 2-3 injections per week produces lower peak blood levels and higher trough levels, which typically means less nausea and more consistent appetite suppression. The total weekly dose stays the same.
What’s the maximum dose of retatrutide?
The highest dose studied in clinical trials is 12mg/week. The 12mg dose produced about 28.3% average weight loss over 80 weeks in the Phase 3 TRIUMPH-1 trial - there’s limited clinical justification for going higher given the side effect increase.
How long does it take to see results on retatrutide?
Measurable weight loss typically begins within the first 4-8 weeks. Noticeable appetite suppression usually starts at the 4mg dose tier (weeks 5-8). Most users report visible body composition changes by weeks 12-16.
Should I take retatrutide with food?
There’s no strict requirement, but many users find that injecting in the evening after a meal reduces nausea compared to injecting on an empty stomach.
Is 1mg of retatrutide enough?
1mg was the lowest arm in the Phase 2 trial and it lost the least of the four doses. For most people 1mg is a tolerance step or a microdose, not a maintenance dose. It is a reasonable place to start if 2mg made you sick. Splitting 2mg a week into two 1mg shots is a different thing: that is still 2mg a week, just spread out. If you feel nothing at 1mg, that is expected: appetite suppression usually shows up at the 4mg tier.
Can I take 2.5mg of retatrutide?
Yes. There is nothing special about 2mg versus 2.5mg; 2mg is just the trial’s starting tier. People land on 2.5mg because at some concentrations it is an easy count: at 5 mg/mL, and only at 5 mg/mL, 2.5mg is 50 units. Check your own concentration before you draw, because the same 50 units at 10 mg/mL would be double the dose. Treat it like a starting dose: hold it for four weeks the way you would 2mg, then step to 4mg, rather than creeping up half a milligram at a time.
How many doses do you get out of a 10mg retatrutide vial?
Five doses at 2mg, two and a half at 4mg, ten at 1mg. Mixed with 2mL of bacteriostatic water a 10mg vial is 5 mg/mL, so 2mg is 40 units and 4mg is 80 units. Reconstituted retatrutide keeps about 28 days in the fridge, which is five weekly shots at most. That makes a 10mg vial the clean fit for 2mg a week: five shots, the last one landing on day 28. Once you are at 8mg a week a 10mg vial covers one shot and change, so move up to a 30mg vial.
How do I know which vial size to use?
Match vial size to your dose so you finish the vial within 28 days, which is five weekly shots at most. At 2mg a week a 10mg vial is the clean fit. At 4mg a week, 20mg. At 6mg or more a week, a 30mg vial and up.
Disclaimer: This article is for educational purposes only and is not medical advice. Retatrutide is not FDA-approved and is currently in Phase 3 clinical trials. The dosing protocols described here are based on published clinical trial data and community experience. Always work with a licensed healthcare provider for dosing decisions and monitoring. Individual responses vary significantly.
Sources
- Jastreboff AM, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial. New England Journal of Medicine, 2023.
- TRIUMPH-1 phase 3 trial of retatrutide in obesity. New England Journal of Medicine, 2024. Reported 25.9% mean weight loss at 9mg/week and 28.3% at 12mg/week.
Ready to track your GLP-1?
- Smart reminders so you never miss a dose
- Track weight, photos, and progress over time
- Medication level curves for every compound
