Forensic toxicology answers a deceptively simple question — what was in this person's body, and how much? — in cases from impaired driving to unexplained death. The honest answer always depends on two things: which sample was tested, and when it was taken relative to exposure.
What toxicology looks for
A toxicology examination can detect and measure:
- alcohol (ethanol),
- drugs — illicit, prescription and over-the-counter,
- poisons and toxic substances.
The sample decides the window
Different samples "remember" for different lengths of time:
- Blood reflects what is active in the body now and best relates a level to impairment or effect.
- Urine shows what has passed through, extending the detection window to days for many substances — but it shows exposure, not current impairment.
- Hair can reveal use over weeks to months, because drugs are laid down in the growing shaft — useful for a history of use, useless for "at the time".
Screen, then confirm
Laboratories work in two stages. A fast, sensitive screening test (often an immunoassay) flags what might be present. Anything of significance is then confirmed with a definitive method — gas or liquid chromatography–mass spectrometry (GC-MS / LC-MS) — which identifies and quantifies the substance precisely. A screen alone is never treated as proof.
Interpretation is the hard part
A number on a report is only the start. Interpreting it requires care:
- tolerance means the same level affects a habitual user and a first-timer very differently,
- drugs break down into metabolites that tell their own story about timing,
- and after death, post-mortem redistribution can shift concentrations, so results must be read in context.
Good toxicology, in other words, pairs sensitive chemistry with cautious interpretation.