Run your own numbers: Tirzepatide Split Dose Calculator
This page shows one fixed split (2.5, then 5, then 10 mg a week, as two injections on day 1 and day 4). Enter your own weekly dose, the days you would inject and your vial to see the dose and syringe units for each injection and the modelled peak and trough against once weekly.
Open the split dose calculator →Key Takeaways
- Compound: Tirzepatide (5.0-day half-life, GLP-1/GIP dual agonist)
- Protocol length: 16 weeks covering 3 dosing phases
- Steady state: Reached in approximately 4 weeks at each dose level
- Split dosing: In the model, two injections per week give a flatter curve than one, with a lower peak and a higher trough for the same weekly total
Tirzepatide Split Dosing: 2x Per Week Protocol
Quick Answer
Tirzepatide has a half-life of 5.0 days. This split-dosing protocol divides each weekly dose into two injections, on day 1 and day 4 of the week. The weekly total is the same, and in the model the level swings less than with once-weekly dosing: a lower peak and a higher trough. No trial has tested whether that changes side effects.
Data computed with the same model and parameters as the GLP3Planner calculators: each dose is absorbed over a day or two and then removed at the rate its published half-life sets. The PK methodology lists every parameter and its source.
Understanding Split-Dose Protocols
A split-dose (or microdosing) protocol divides your total weekly dose into two or more smaller injections spread throughout the week. The total amount of drug per week stays the same. What changes is the peak-to-trough ratio: the difference between the highest and lowest drug levels in your body between injections.
With once-weekly dosing, Tirzepatide levels rise for a day or so after each injection and then fall until the next dose 7 days later. That creates a "sawtooth" pattern. Splitting the dose into smaller, more frequent injections flattens that pattern in the model. No trial has tested whether a flatter curve changes side effects.
No clinical trials have specifically studied split-dosing for Tirzepatide. This approach is based on pharmacokinetic principles and community experience. The PK model below shows the calculated levels for this protocol so you can see the expected peak and trough at each phase. It is the same model the Tirzepatide split-dose calculator uses, including the day or two each dose takes to absorb; the calculator shows the peak and trough for your own weekly dose and injection days. For a deeper look at microdosing, see the Tirzepatide microdosing guide.
Dosing Protocol
| Phase | Weeks | Dose | Frequency | Peak (mg) | Trough (mg) | Syringe Units |
|---|---|---|---|---|---|---|
| 2.5mg/week split | 1-4 | 1.25mg | 2x/week | 2.38 | 1.51 | 12.5 units |
| 5mg/week split | 5-8 | 2.5mg | 2x/week | 4.8 | 3.11 | 25 units |
| 10mg/week split | 9-16 | 5.0mg | 2x/week | 9.71 | 6.4 | 50 units |
Peak and trough are the highest and lowest modelled amounts in the last week of each phase, from the same model and parameters as the calculators (5.0-day published half-life). See methodology.
What the Numbers Mean
The table above shows modeled drug levels at each phase of this protocol. Here is what each column tells you:
Peak (mg)
The highest modelled amount of Tirzepatide in your body in the last week of that phase, reached a day or two after an injection once the dose has been absorbed. In a phase with no injection it is the level at the start of the week.
Trough (mg)
The lowest modelled amount in the last week of that phase, reached just before an injection. This is the minimum drug level in the model between doses.
Steady State (~4 weeks)
The point where drug accumulation stabilizes. Before steady state, each dose adds more drug than your body eliminates, so levels keep climbing. Once reached, the amount in equals the amount out, and your peaks and troughs become consistent from week to week.
These are population-average estimates from the model's parameters, each listed with its source in the methodology. Individual levels vary based on body composition, metabolism, and injection site. For a personalized view, enter your actual doses into the Tirzepatide calculator.
Pharmacokinetic Summary
Half-Life
5.0 days
Time for 50% of the drug to be eliminated
Steady State
~4 weeks
Time to reach stable peak/trough levels at each dose
Final Peak Level
9.71 mg
Peak drug amount in the last phase (10mg/week split)
Model Your Own Schedule
Enter your actual doses and timing to see a personalized PK curve with your real data.
Open Tirzepatide CalculatorReconstitution Reference
Based on a 30mg vial with 3mL BAC water (10mg/mL):
| Dose | Syringe Units (U-100) | Volume (mL) |
|---|---|---|
| 1.25mg | 12.5 units | 0.125mL |
| 2.5mg | 25 units | 0.25mL |
| 5.0mg | 50 units | 0.5mL |
Units are the marks on a U-100 insulin syringe (1 unit = 0.01mL), not international units.
Need a different concentration? Use our reconstitution calculator. For step-by-step instructions, see the Tirzepatide reconstitution guide.
Practical Tips for This Protocol
Split Dosing Technique
Splitting doses requires drawing smaller volumes from a reconstituted vial. Accuracy matters more when the injection volume is small.
- Use higher-concentration vials: With split dosing, each individual injection is a smaller volume. A more concentrated reconstitution (less BAC water) makes it easier to draw the correct amount on an insulin syringe.
- Consistent spacing: For twice-weekly protocols, aim for roughly even spacing (e.g., Monday/Thursday or Tuesday/Friday). The exact days matter less than keeping the interval consistent.
- Comparing peak/trough: Splitting changes the shape of the modelled curve, not the weekly total; no trial has tested whether it changes side effects.
- Track your schedule: Use the Tirzepatide calculator to model your exact split protocol and compare it visually to once-weekly dosing.
Common Side Effects
In the SURMOUNT-1 trial, the most common side effects of tirzepatide were gastrointestinal: nausea (24-33%), diarrhea (18-23%), and constipation (17-23%) depending on dose. Most events were mild to moderate and occurred during titration.[3]
Nausea
Most common during the first few days after an injection or dose increase. Smaller meals, bland foods, and staying hydrated can help. Some people find evening injections reduce daytime nausea.
Digestive Changes
Diarrhea or constipation may occur as the drug slows gastric emptying. Adequate fiber, water, and gentle activity help regulate digestion. These effects typically improve within the first 2-3 weeks at each dose.
Reduced Appetite
This is an expected effect, not a side effect. Make sure you are still eating enough protein and nutrients even when appetite is suppressed. Skipping meals entirely can lead to fatigue and muscle loss.
For a comprehensive list including less common effects, see the full Tirzepatide side effects guide.
See Your Own Levels
Enter your actual doses and schedule to get a personalized PK curve.
How This Data Was Computed
Levels come from the same pharmacokinetic model as the GLP3Planner calculators, with the same parameters: each dose is absorbed from under the skin over a day or two, only the bioavailable share reaches the body, and the body removes it at the rate the 5.0-day published half-life sets. Doses are added together (superposition) in 1-hour steps to show how weekly doses accumulate. The figures are modelled amounts in milligrams, not blood test results. Read the full methodology, including data sources and model limitations.
Frequently Asked Questions
How long does Tirzepatide stay in your system?
Tirzepatide has a half-life of about 5 days. After your last dose the level keeps rising for a day or so while that dose is absorbed, then falls with the 5-day half-life. In the model, after weekly doses the level is below 3% of that peak (about 97% gone) by day 27 after the last dose. By half-life arithmetic, five half-lives (25 days) would leave 3.125%; absorption adds about a day in the model. Some drug remains after that. Use the Tirzepatide washout calculator to see the modelled dates for your own dose and last injection.
What is steady state for Tirzepatide?
Steady state is when drug accumulation stabilizes, meaning the amount entering your system each dose roughly equals the amount eliminated between doses. For Tirzepatide, this takes approximately 4 weeks of consistent dosing at the same level. Once at steady state, your peak and trough levels become predictable from week to week.
Is split dosing as effective as once-weekly injection?
The total weekly dose determines average blood levels and overall exposure, which should be similar regardless of how the dose is divided. However, no clinical trials have compared split-dosing to once-weekly for Tirzepatide specifically. The approach is based on pharmacokinetic modeling and community experience.
How accurate is the pharmacokinetic data on this page?
The data uses population-average parameters: the half-life, time to peak and bioavailability listed with their sources in the methodology. Individual drug levels vary based on body composition, metabolism, kidney and liver function, and injection site. The model is most useful for understanding accumulation patterns, steady state timing, and comparing dosing approaches rather than predicting exact personal blood levels. See the full methodology for details.
What is the peak-to-trough ratio and why does it matter?
The peak-to-trough ratio measures how much drug levels fluctuate between injections. For once-weekly Tirzepatide at steady state, the model's ratio is about 2.2:1: the peak is about 2.2 times the trough. Higher ratios mean bigger swings between injections. Split dosing reduces this ratio in the model by producing smaller, more frequent peaks.
Can I use this data to plan my own dosing schedule?
This data is for informational and educational purposes. It shows modeled drug levels for a specific protocol, which can help you understand what to expect and have informed conversations with your doctor. For a schedule tailored to your exact doses, use the interactive Tirzepatide calculator.
References
- Jastreboff AM, Kaplan LM, Frias JP, et al. Triple-hormone-receptor agonist retatrutide for obesity: a Phase 2 trial. N Engl J Med. 2023;389(6):514-526. PubMed
- Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity. N Engl J Med. 2021;384(11):989-1002. PubMed
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity. N Engl J Med. 2022;387(4):327-340. PubMed
- Novo Nordisk. Ozempic (semaglutide) prescribing information. U.S. Food and Drug Administration. FDA Label
- Eli Lilly and Company. Mounjaro (tirzepatide) prescribing information. U.S. Food and Drug Administration. FDA Label
- Urva S, Coskun T, Loh MT, et al. LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes: a phase 1b trial. Lancet. 2022;400(10366):1869-1881. PubMed
- StatPearls. Pharmacokinetics, Steady State. National Center for Biotechnology Information. NCBI Bookshelf
- Coskun T, Urva S, Roell WC, et al. LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: from discovery to clinical proof of concept. Cell Metab. 2022;34(9):1234-1247.e9. PubMed
- Novo Nordisk. Wegovy (semaglutide) prescribing information, sections 2.2 and 2.4. DailyMed. DailyMed
- Eli Lilly and Company. Zepbound (tirzepatide) prescribing information, sections 2.1 and 2.3. DailyMed. DailyMed
Medical Disclaimer
This page is for informational and educational purposes only. It does not constitute medical advice, diagnosis, or recommendations. The pharmacokinetic data shown is modeled from population-average clinical trial parameters and does not predict individual drug levels. Always consult your doctor before starting, adjusting, or stopping any medication.
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