Why simulate before you escalate
Retatrutide has a 161-hour terminal half-life and a four-day Tmax. That means today's injection won't reach peak concentration for four days, won't reach steady state for several weeks, and will still be measurable a month after you stop. Reactive dose changes — "I'll just bump it up this week" — produce overshoots that show up as nausea two weeks later. The simulator lets you preview the consequence before you take the shot.
Three simulation modes
1. Escalation preview
Pick a future date and a target dose. The simulator extends your real PK curve forward at the new dose and shows the projected steady-state level. Compare it side-by-side with your current dose to see exactly how much higher (or lower) the new protocol will push your concentration.
2. Skip-week recovery
Travel, illness, or vial gaps happen. The simulator models a forced skip and shows when you'd return to your previous level if you (a) resumed at full dose, (b) stepped down for one week to soften the re-up, or (c) extended the gap further. The visual makes the right choice obvious.
3. Split-dose comparison
Some users prefer a half-dose every 3.5 days instead of a full dose weekly to flatten side-effect peaks. The simulator overlays both schedules so you can see how much smoother the resulting curve actually is — and whether the steady-state plateau changes (it shouldn't, given the long half-life).
Half-life 161 hours · Volume of distribution 47 L · Tmax 4 days · Linear two-compartment model. Source: Coskun T et al., 2022. The simulator's accuracy was validated against published PK at ±10% across the 1.5–12 mg dose range.
What the chart shows
- Solid line — modeled retatrutide concentration from your real dose history.
- Dashed line — modeled concentration from the hypothetical protocol you've entered.
- Shaded band — the 95% prediction interval from inter-individual variability in the published PK study.
- Markers — every dose, real or simulated, with its mg amount.
Limitations to keep in mind
The simulator models pharmacokinetics — drug concentration over time. It does not model pharmacodynamics — how that concentration translates to appetite suppression, weight loss, or side effects. Two users at the same level can have very different responses. The chart is a useful planning tool, not a clinical prediction.
The simulator also assumes you'll follow the protocol you enter. Real-life adherence is messier. The "skip a week" scenario is often closer to reality than the "perfectly weekly" scenario, especially in months 2–3.
Frequently asked questions
Is the simulator different from the dose calculator?
Yes. The calculator at /calculator answers "what's my level today and what's a typical next dose?" — a single recommendation. The simulator answers "what would happen if I changed my schedule starting next week?" — a forward projection across many days.
How accurate is ±10%?
The simulator was validated against the published Coskun 2022 PK study at ±10% across the 1.5–12 mg dose range. Inter-individual variability in real users is wider — clearance varies by body composition and renal function. Treat the chart as a precision tool for ordering protocols, not for predicting your absolute level to two decimal places.
Can I save a simulation?
Yes. Each simulated protocol can be named and saved as a draft. You can revisit it later and compare it to how reality unfolded if you adopted it.
Does it work on retatrutide-specific dose strategies like reverse titration?
Yes — any schedule expressible as date + mg pairs works. Reverse titration (start higher, taper down to find your minimum effective dose) is a common simulator use case.