Forensic toxicology is carried out as part of a criminal investigation commonly involving police and other forensic services. Toxicological analyses are used to examine the possibility of drug use playing a part in what happened.
Samples for toxicological examination are taken in relation to a number of crimes, including homicide, assault and rape. Analyses are carried out to determine the possible use of drugs (legal or illicit) that may affect the mind, alter the mood or cause sleep.
Blood and urine samples are obtained from the living:
- from victims of assault or rape;
- from victims of suspected drug assisted sexual assaults, generally where there has been some memory loss of events;
- from the suspected perpetrator of a crime (these samples are not obtained often as frequently the perpetrator is found too long after an event for analysis of samples to be of any use);
- from drivers of motor vehicles who may have killed a passenger, drivers of other cars, pedestrians or cyclists.
Drug levels
The significance of drugs in samples taken from the living is more difficult to interpret than samples taken from the dead. While a person lives, drug levels drop, as the drug is metabolised and excreted. Drug levels don’t change to a significant extent in dead people. The longer the delay between the incident and the time of sample taking, the more difficult it is to interpret the significance of drug findings.
Drugs can be detected in urine for a longer time than in blood, and levels are generally higher in the urine than in blood. Some drugs may be present in the urine for several days after drug use. However, no interpretation as to the effect of a drug can be made from detection of a drug in the urine. It is only possible to say that the drug has been used and when it is likely to have been used.
Drugs are present in the blood for shorter periods than in urine and it is usually possible to estimate how recently the drug might have been used. The level of a drug in blood depends on how much was taken and how quickly it is excreted from the body. It is sometimes possible to calculate, very roughly, a possible level at the time of an incident. This may also reveal that a drug was taken after the event.
It is usually possible to find out about the types of effects that a drug might be expected to have on a person. However, it is not possible to say that a person will be affected by a drug in a particular way. It is not possible to relate a drug level to a particular effect or behaviour. Individuals are affected by drugs in different ways and may exhibit different behaviours in different circumstances.
Hair Analysis at ESR (PDF, 919KB)