GlossaryPharmacokineticsCmax
Pharmacokinetics

Cmax

Also known as: peak concentration · maximum plasma concentration

Cmax is the highest concentration a drug reaches in your blood after a dose; Tmax is how long after the dose that peak occurs.

Cmax (maximum concentration) is the peak of the concentration-time curve, read directly from measured blood samples rather than estimated between them. It is paired with Tmax, the time after dosing when the peak occurs. In bioavailability studies, FDA guidance uses AUC to describe how much drug was absorbed and Cmax and Tmax to describe how fast. Because Cmax is a single observed point, it depends on when blood was drawn: if the first sample is taken too late, the real peak can be missed.

After a SubQ injection the peak arrives slowly, and how slowly varies a lot by compound. Liraglutide reaches its maximum 8 to 12 hours after a dose; tirzepatide's Tmax ranges from 8 to 72 hours. With repeated dosing, each new dose lands on what remains of the earlier ones, so the steady-state Cmax ends up higher than the first-dose Cmax.

Why it matters

Cmax and total exposure (AUC) can move independently. In the tirzepatide label, a first 5 mg dose of tirzepatide cut the Cmax of oral acetaminophen by 50% and pushed its peak 1 hour later, while total acetaminophen exposure (AUC over 24 hours) was not changed; by week 4 there was no meaningful effect on Cmax. Same total exposure, lower and later peak.

If an effect or side effect seems to track the hours after each injection, peak concentration is a more useful lens than total exposure. Keep in mind that any published Cmax belongs to its dose, route and population: liraglutide's label Cmax of 35 ng/mL is for a single 0.6 mg SubQ dose and does not describe other doses, steady state, or other compounds.

How to read it

  1. Note the dose, route, population and whether the Cmax is single-dose or steady-state.
  2. Check Tmax to see how long after dosing the peak occurs.
  3. Scale a Cmax to another dose only if the source states exposure is dose-proportional over that range.
  4. For repeated dosing, estimate how much higher levels climb with the accumulation ratio R.

Accumulation ratio R = 1 / (1 − 0.5^(τ / t½)), where τ is the dosing interval (simple one-compartment model)

Worked example

Liraglutide's label reports a single-dose Cmax of 35 ng/mL at 0.6 mg and dose-proportional Cmax from 0.6 to 1.8 mg, so a single 1.2 mg dose would be expected near 35 × 2 = 70 ng/mL. Accumulation for tirzepatide (t½ about 5 days, dosed every 7 days): 0.5^(7/5) = 0.379, so R = 1 / (1 − 0.379) = 1 / 0.621 ≈ 1.6. For liraglutide (t½ about 13 hours, dosed every 24 hours): 0.5^(24/13) = 0.278, so R = 1 / 0.722 ≈ 1.4. These are model estimates, not measured values.

Common mistakes

  • Comparing Cmax values from different doses, routes or species as if they were the same measurement.
  • Assuming the first-dose peak is what you will see later; with repeated dosing, levels accumulate until steady state.
  • Treating Cmax and AUC as interchangeable; slower absorption can lower the peak while total exposure stays the same.
  • Expecting a SubQ peak within minutes; for liraglutide and tirzepatide it takes hours to days.
  • Trusting a Cmax from sparse blood sampling; the real peak may fall between samples.

Sources

  1. GuidelineBioavailability Studies Submitted in NDAs or INDs — General Considerations: Guidance for Industry. U.S. Food and Drug Administration (CDER), 2022.
  2. Prescribing informationVICTOZA (liraglutide) injection, for subcutaneous use: Prescribing Information. Novo Nordisk (FDA-approved labeling), 2025.
  3. Prescribing informationMOUNJARO (tirzepatide) injection, for subcutaneous use: Prescribing Information. Eli Lilly and Company (FDA-approved labeling), 2026.

Page updated . How we grade evidence: methodology.

Related Terms

Cmin

Cmin is the lowest concentration of a drug in your blood during a dosing interval, usually reached just before the next dose (the trough).

AUC (Area Under Curve)

AUC (area under the curve) is your total exposure to a drug over time: the area under its blood concentration-time curve.

Half-Life

Half-life (t½) is the time it takes for the concentration of a drug in your blood plasma to fall by half.

Titration

Titration is starting a drug at a low dose and raising it in planned steps, so your body can adjust and side effects stay manageable.

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