Blood Level Calculator

Each intake decays independently and the curve is their sum. For one substance:

amount(t) = Σ  F·D_i · ka/(ka − ke) · ( e^(−ke·(t−t_i)) − e^(−ka·(t−t_i)) )
            i

  F   bioavailability for the route taken — how much reaches the bloodstream
  ka  absorption rate, solved from that route's published Tmax
  ke  elimination rate = ln2 / half-life
  t_i time of intake i; terms with t < t_i contribute nothing

A one-compartment model with first-order absorption and elimination. The dose has to be absorbed before it can act, so the curve starts at zero, climbs to a peak at roughly the substance’s Tmax, and only then decays — an intravenous dose is the exception, and skips straight to the peak because it is already in the blood.

The Type and Time After Meal columns both feed into this. Route changes how much is absorbed and how fast — swallowed nicotine largely does not survive first-pass metabolism, while inhaled nicotine peaks within minutes. Food delays gastric emptying, so an intake logged within two hours of a meal absorbs more slowly: ibuprofen’s peak arrives about twice as late and noticeably lower, though the total exposure is unchanged. For a few substances food genuinely reduces the total too, which is why omeprazole is taken before breakfast.

Ethanol gets its own equation. It has no half-life: alcohol dehydrogenase saturates far below the concentration of a single drink, so it is cleared at a near-constant rate of roughly 8.5 g/h for a 70 kg adult. It is modelled as Michaelis-Menten (Vmax 8.5 g/h, Km ≈ 80 mg/L) and integrated numerically, because non-linear elimination means separate drinks do not simply add up. Everything else here is adult population averages and individuals vary widely — caffeine alone ranges from about 2 to 10 hours depending on CYP1A2 activity, smoking, pregnancy and oral contraceptives. Educational tool, not medical or dosing advice.