What is Toxicology?

Toxicology is the analysis of blood and urine for the presence of alcohol, drugs and solvents.  A toxicologist will analyse samples to detect the presence of a substance, identify what it is and determine how much of the drug is present i.e. the purity. Toxicology analysis will detect a wide range of drugs present in a sample. This may be prescription or illicit drugs.

A toxicologist works closely with the investigating officers to determine the type of analysis required.

Toxicology analysis is split into two main areas namely postmortem and ante mortem.

Postmortem (sometimes referred to as morbid toxicology)

Toxicology is used in cases of sudden death and fatal accident enquiries.  If someone dies suddenly the pathologist will send samples to toxicology to assist him to establish cause of death or even the deceased's frame of mind. If someone is killed in a road accident it is routine to test for the existence of drugs and alcohol. In cases of murder where someone is attacked and subsequently dies, toxicology analysis can determine whether the attacker was under the influence when committing the offence and how this would affect their behaviour which may feature as part of their defence.

Ante mortem (referred to as criminal toxicology)

This is when biological samples are analysed in relation to murders, assaults, drug assisted sexual assaults and road traffic offences. Toxicology can also help determine if alcohol, drugs or solvents are contributing factors when someone commits an offence.   

Determining the Effects

The effects of drugs and alcohol depend on many different things. Every person is different and individuals all have different tolerances to drugs and alcohol depending on whether they are heavy drinkers, drug users or regularly taking a prescription drug.  The range of available drugs is huge. However the majority of prescription drugs have published data that reports the therapeutic and fatal ranges. 
Occasionally in road traffic offences the accused will leave the scene of the crime, go home and then consume more alcohol.  However a toxicologist is still able to determine what the alcohol level would have been at the time of the crash, taking into consideration things like the height and weight of the accused.

When it comes to deciding how much alcohol we can have and drive safely the best advice is not to take any alcohol at all because you don't know how it is going to affect you.


Gas or liquid gas chromatography with mass spectrometry is used to analyse samples.

Once the analysis is complete a toxicologist will prepare a report for the Crown.  The report will state the precise amount and the type of drug(s) found and a percentage to show purity.