Synthesis · Absorption · Clearance · Accumulation · assembled from label pharmacokinetics and standard compartmental theory, not a reading of one paper
This is a synthesis, not a close reading: it assembles the published pharmacokinetics of tirzepatide into a working model you can move. A half-life near five days and a dosing interval of seven means each injection lands on top of what is left of the previous ones. Levels climb for weeks after nothing about the prescription has changed, and the standard escalation ladder restarts that climb every time the dose goes up.
The curve below is modelled milligrams in the body, not a blood test. It is a quantity no laboratory reports and this page does not predict one. What it is good for is shape: how long the climb lasts, how deep a missed injection cuts, and how much of the sawtooth is real.
This page describes mechanism. It is not medical advice, it is not a dosing tool, and reading it creates no clinical relationship. Dosing, escalation, missed doses, and every safety question belong with your own prescriber, who knows things about you that a population average cannot.
one-compartment model, first-order absorption and elimination
k_e = ln2 / t_half
t_max(k_a) = ln(k_a / k_e) / (k_a - k_e) solved numerically for k_a
A(t) = sum over injections i already given of
F * D_i * k_a/(k_a - k_e) * ( exp(-k_e*u) - exp(-k_a*u) ), u = t - t_i
A_ss = F * D / (k_e * interval) average at steady state
t_ss ~ 4 to 5 half-lives
| Quantity | Value here | Tier | Where it comes from |
|---|---|---|---|
| Absolute bioavailability, F | 0.80 | Measured | Mounjaro prescribing information, section 12.3. Reported as a mean of 80% after subcutaneous administration. |
| Elimination half-life | ~5 days | Measured | Section 12.3, and confirmed independently by the population model in Schneck 2024 across 19 pooled studies. |
| Half-life slider range | 4 to 7 days | Chosen | Not a published confidence interval. A plausible spread, put on a control so the reader can see how little the shape depends on it. |
| Time to peak, t-max | 8 to 72 h | Measured | Section 12.3 gives this as the observed range. The default of 34 h sits near the middle of it. |
| Absorption constant, k-a | derived | Chosen | Not published anywhere. Solved from your t-max and k-e, which is why t-max is the control and k-a is only the readout. |
| Apparent clearance | 0.061 L/h | Measured | Section 12.3. Used here only as a cross-check: 0.061 divided by the 10.3 L apparent volume gives a half-life of 4.9 days, which agrees with the stated 5. |
| Apparent volume | 10.3 L | Measured | Section 12.3, mean apparent steady-state volume in type 2 diabetes. Not used to draw the curve. |
| Escalation ladder | +2.5 mg / 4 wk | Measured | Section 2.1: start at 2.5 mg weekly, increase to 5 mg after 4 weeks, then in 2.5 mg increments after at least 4 weeks on the current dose, to a maximum of 15 mg. |
| Number of compartments | 1 | Simplified | The published population model is two-compartment (Schneck 2024). One compartment reproduces accumulation and the weekly sawtooth but flattens the early distribution phase after each injection. |
| Between-person variability | none | Simplified | Every curve here is one population-average person. Body weight is the largest covariate in the published model and is not represented at all. |
Each injection contributes a rise over roughly one to two days followed by a slow decline, and the curve is the sum of every injection so far. Because seven days is only about 1.4 half-lives, most of a dose is still present when the next one arrives. Levels therefore climb until what goes in each week equals what is cleared each week, which takes four to five half-lives: roughly 20 to 25 days at a five-day half-life. The label states the same thing from the measurement side, that steady-state concentrations were reached after four weeks of once-weekly dosing.
Settling does not mean flat. At 5 mg weekly with a five-day half-life the model puts the steady-state average near 4.1 mg, with the weekly peak around 5.5 mg and the trough just under 2.6 mg: a swing of more than two to one across a single week. That ratio is set almost entirely by the interval divided by the half-life, which is why the interval slider moves the sawtooth far more than the half-life slider does.
The escalation ladder is the part people underestimate. Every step up restarts a shorter version of the same climb, so someone titrating from 2.5 to 15 mg is not at their final exposure until roughly a month after the final increase, which can be five or six months after the first injection. Turn the ladder off and set the target directly to see the difference between the two stories.
Skipping one injection carves a dip that refills over about two weeks rather than resetting anything, which is the single most useful intuition the model offers. It is also where the model is weakest: it says nothing about tolerability, which is what actually governs escalation and what actually happens when someone restarts after a gap. A pharmacokinetic curve is not a clinical plan.
Three further limits worth holding onto. The vertical axis is amount in the body, not plasma concentration, so it cannot be compared against any assay result. The single compartment smooths a distribution phase that the published two-compartment model resolves, which mostly affects the first day or two after each injection. And there is no variability: real exposure at a fixed dose spans a wide range across people, with body weight the dominant driver, so the height of this curve is the least trustworthy thing on the screen. The shape is what survives.
Scope: this page models the shape of tirzepatide accumulation under repeated subcutaneous dosing. The pharmacokinetic constants are label figures and are attributable to the sources above. Everything the curve displays is a computed consequence of those constants under a deliberately simplified one-compartment model applied to a single population-average person, not a measurement, not a prediction for any individual, and not comparable to a laboratory result. Nothing here is medical advice.