Abstract
Laboratory evidence of the presence and concentration of a drug in a person who has come to harm is often helpful in forensic pharmacology, and may be crucial. However, its value depends on two critical interpretations by the expert. First, the expert must make a careful analysis of the relationship between the results as measured in the sample and the drug in the patient at the time that harm occurred. That is especially difficult with post-mortem samples. Secondly, the expert must syntheses the laboratory information with the available clinical history and clinical or pathological findings. Even in the most favourable circumstances, when the sample is correctly obtained, identified, and analyzed, it can be hard to say that beyond reasonable doubt a given concentration had a given effect.