Chemistry Meets Justice
Forensic toxicology bridges analytical chemistry and the legal system. When a person dies under suspicious circumstances, or when impairment is suspected in a crime or accident, toxicologists analyze blood, urine, vitreous humor, and tissue samples to identify and quantify drugs, poisons, and metabolites. The results can determine cause of death, establish impairment, or reveal poisoning — often providing the decisive evidence in court.
Pharmacokinetic Modeling
The concentration of a drug in the body follows predictable mathematical patterns. After absorption, the blood concentration rises to a peak (Cmax), then declines exponentially as the body eliminates the drug. The elimination half-life — the time for concentration to halve — is characteristic of each substance: alcohol has t½ ≈ 0.5h, cocaine t½ ≈ 1h, morphine t½ ≈ 3h, diazepam t½ ≈ 40h. This simulation models the concentration-time curve using one-compartment pharmacokinetics.
Interpretation Challenges
Converting a blood concentration to a forensic conclusion is not straightforward. Tolerance means that a level lethal to a naive user may be unremarkable in a chronic user. Postmortem redistribution can raise or lower concentrations after death. Drug interactions can amplify effects synergistically. Forensic toxicologists must consider the full clinical picture, not just numbers, when forming opinions for court.
Detection Windows
Different drugs remain detectable for different periods. Alcohol clears within hours; cocaine metabolites persist for 2–3 days in urine; cannabis metabolites may be detectable for weeks in heavy users. Hair analysis can detect drug use months after exposure. The choice of specimen and analytical method determines what the toxicologist can and cannot find, making sampling strategy a critical decision in forensic investigations.