Substance Half-Life Calculator

How long does a substance stay detectable?

The calculator uses pharmacokinetic half-life (t½): after 5 half-lives, the plasma concentration drops to roughly 3% of the initial dose — a common threshold to consider the substance practically eliminated. Detection in lab tests, however, depends on the matrix: urine often holds metabolites longer than blood. Typical detection windows: cannabis (THC) 3–30 days in urine (occasional vs chronic), ~90 days in hair; cocaine 2–4 days urine, ~90 days hair; anabolic steroids weeks to months (especially nandrolone, stanozolol); caffeine half-life ≈ 5 h; alcohol on the breath 12–24 h.

Applications

Reference for sports doping screening (the World Anti-Doping Agency, WADA, maintains the official Prohibited List; Brazilian athletes are monitored by the ABCD), workplace drug tests, clinical decisions about drug interactions and washout periods. The values are estimates: weight, hydration, metabolism, frequency of use, body fat and genetics change the actual window significantly.

FAQ

Why are urine and hair windows so different? Hair incorporates substances into the keratin matrix as it grows, preserving a history. Urine reflects recent excretion of metabolites.

Can I speed up elimination? Half-life is governed by liver and kidney function. Hydration and exercise have a marginal effect; there is no reliable "detox" shortcut.

Are these numbers legal proof? No — official anti-doping or forensic testing uses validated laboratory protocols. This tool is for educational reference only.