Reading a PK Curve

Every chart on this site plots the same thing: estimated blood concentration on the vertical axis against time on the horizontal axis. Here’s how to read one like a pharmacologist.

The shape

After a single dose, a concentration curve rises to a peak (Tmax) and then falls as the body clears the drug. The fall is described by the half-life — the time for concentration to drop by 50%.

Peaks and troughs

With repeated dosing, each new dose lands on top of residual drug. The result is a sawtooth of peaks (right after a dose) and troughs (right before the next dose). Over time, both peaks and troughs climb until they plateau at steady state.

What steady state means

At steady state, the amount of drug cleared per dose interval equals the amount administered. Trough concentration — not peak — is usually what predicts efficacy for hormones like testosterone and peptides like GLP-1s.

What the curve can’t tell you

Our model is a simplified one-compartment approximation. It can’t capture:

• Tissue-specific distribution
• Protein-binding saturation
• Active metabolites
• Individual genetic variation

Read the curve for relative patterns — accumulation, timing, peak-to-trough swings — not as a prediction of your exact blood level. See our methodology page for the full limitations.