GLP-1 Half-Life & Dose Level Calculator
Visualize how Retatrutide, Tirzepatide, or Semaglutide accumulates in your system over time. See exactly when you'll reach steady state and how dose titration affects total drug levels.
Based on published pharmacokinetic data. Individual results vary. For research purposes only.
Why Drug Accumulation Matters
GLP-1 agonists like Retatrutide, Tirzepatide, and Semaglutide are dosed weekly — but their half-lives range from 5 to 7 days. This means each new dose is injected while there's still significant residual drug from previous doses.
The result: drug levels accumulate week over week until reaching a “steady state” — where the amount eliminated between doses equals the amount injected. This typically takes 4–5 weeks at each dose level.
Half-Life Data by Drug
| Drug | Half-Life | Steady State | Dosing |
|---|---|---|---|
| Retatrutide | ~144h (6 days) | ~4–5 weeks | Once weekly |
| Tirzepatide (Mounjaro/Zepbound) | ~120h (5 days) | ~3–4 weeks | Once weekly |
| Semaglutide (Ozempic/Wegovy) | ~168h (7 days) | ~4–5 weeks | Once weekly |
What This Means for Titration
If you inject 2mg of Retatrutide on week 1 and don't feel much, you might be tempted to jump to 4mg the next week. But there's still approximately 1.2–1.5mg from your first dose still circulating. So your effective dose is closer to 5–5.5mg — not 4mg. This is why slow titration (increasing every 4 weeks) is essential. The calculator helps you visualize exactly what's happening.