The forensic toxicologist deals mainly with providing information to the legal system on the effects of drugs and poisons. They are often very senior toxicologists who have gained a lot of experience in other areas of toxicology first, such as analytical chemistry.
Having gathered and evaluated the available toxicological evidence, they may attend court as an expert witness to describe and explain the evidence relating to the case. These can range from simple ‘drink-driving’ cases to fatal accident, suicide and murder investigations, where deliberate or accidental poisoning is suspected.
Forensic toxicologists use modern analytical procedures to isolate, identify and quantify drugs, endogenous compounds and poisonous substances in forensic samples. Often, only very small quantities of sample can be retrieved from the crime scene or the mortuary, and the sample matrix can vary widely, to include body fluids, plant materials and drug paraphernalia. They must assess the significance of these analytical data so as to identify relationships between exposure levels and clinical response. It is necessary to understand how the metabolism of a chemical can affect its concentration and pharmacological or toxic effects. It is also important to consider factors such as drug-drug interactions, tolerance, age related effects, post-mortem redistribution and differences between individuals. It can be necessary for forensic toxicologists to conclude a probable cause of death in post-mortem cases.