GLP-1 Plasma Level Plotter: Complete Guide
The Plasma Level Plotter simulates the rise, peak, and decay of GLP-1 plasma concentrations over weeks of dosing. Built on a one-compartment subcutaneous absorption model with published population pharmacokinetic parameters for semaglutide, tirzepatide, and retatrutide. This guide explains what the plotter shows, how the math works, and what the visual patterns mean for your dosing.
1) What the Plotter Shows
- Plasma concentration curve over the simulation window
- Injection markers with mg labels at each dose
- TODAY line showing where you are right now in the curve
- Steady-state region visible as the flatter plateau after several doses
- Multi-compound view when your log mixes sema/tirz/reta — each gets its own color
- Trend-aware coloring — line color reflects whether exposure is rising, stable, or declining
2) The Math (One-Compartment Model)
Each injection contributes a Bateman-impulse curve to the total plasma level. The formula:
Where ka is the absorption rate constant and ke is the elimination rate constant. Per-compound values used:
| Compound | Half-life (t½) | ke | ka |
|---|---|---|---|
| Semaglutide | ~7 days | ln(2)/7 | 0.80/day |
| Tirzepatide | ~5 days | ln(2)/5 | 1.20/day |
| Retatrutide | ~6 days | ln(2)/6 | 0.65/day |
Total plasma level at time t = sum of all dose contributions.
What the Patterns Mean
- Rising curve, no plateau yet → you're still accumulating. First 4–6 doses for semaglutide, 3–5 for tirzepatide. Side effects often peak during this phase.
- Curve flattens (plateau) → you've hit steady-state at this dose. New side effects rare from here unless you escalate.
- Saw-tooth pattern → normal weekly cycles. Peak 24–48h post-injection, trough just before next dose.
- Falling fast after a missed dose → trough drops below previous lows; appetite returns; nausea may recur on next injection.
- Mixed compound curves → see individual contributions in the multi-compound view.
Common Use Cases
- Predicting when peak plasma levels (and worst nausea) will hit
- Visualizing the effect of a missed dose
- Comparing weekly vs split-dose (microdose) protocols
- Planning when to escalate based on steady-state achievement
- Sharing your protocol curve with your prescriber via the share link
Plot your protocol
Add doses, see the curve. Free, no sign-up.
Limitations to Know
- Population-average PK params — your individual half-life may be ±30%
- One-compartment model is an approximation; real GLP-1 PK is two-compartment
- Doesn't account for body composition, metabolism, or injection site variance
- Y-axis is relative scale, not absolute ng/mL
- Use as a directional reference, not a clinical instrument
Frequently Asked Questions
What pharmacokinetic model does the GLP-1 plotter use?
The plotter uses a one-compartment subcutaneous absorption model with published population pharmacokinetic parameters. Each injection contributes a Bateman impulse curve, and the total plasma level at any time is the sum of all dose contributions. The math reflects standard pharmacology textbook formulas.
What half-life values does the GLP-1 plotter use for each compound?
Semaglutide uses a 7-day half-life with absorption rate 0.80/day, tirzepatide uses 5 days with absorption 1.20/day, and retatrutide uses 6 days with 0.65/day. These values come from published population PK studies and feed the Bateman equation that drives the simulated curve.
What does a saw-tooth pattern on the GLP-1 plotter mean?
Saw-tooth shape reflects normal weekly dosing cycles: peak concentration at 24-48 hours post-injection followed by gradual decline to a trough just before the next dose. This is the expected pattern at steady-state and indicates consistent dosing without unusual gaps or missed injections.
What are the limitations of the GLP-1 plasma level plotter?
Population-average PK parameters mean your individual half-life may vary by 30%. The one-compartment model approximates real two-compartment GLP-1 kinetics. It does not account for body composition, metabolism, or injection-site variance, and the y-axis is relative scale, not absolute ng/mL.
How long does it take to reach steady-state on a GLP-1?
About 4-6 doses for semaglutide and 3-5 for tirzepatide based on the half-life math. The curve rises during these initial doses and then flattens into a plateau. Side effects often peak during this accumulation phase and become rare after steady-state unless you escalate to a higher dose.