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What is Toxicology?

Toxicology is the analysis of blood, urine and other samples for the presence of alcohol, illicit drugs, medicines and other toxins. A toxicologist will analyse samples to confirm the presence of a toxin, identify what it is and determine how much is present i.e. the concentration. Toxicology analysis will detect a wide range of substances present in a sample.

A toxicologist works closely with police, pathologists and the Crown Office and Procurator Fiscals Service to determine the type of analysis required.

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

Postmortem Toxicology (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 them in establishing the cause of death or even the deceased's frame of mind. If a substance is detected, the pathologist will ascertain if this was a contributory factor in the death. If someone is killed in a road accident, it is routine to test for the existence of drugs and alcohol.

Ante mortem Toxicology (referred to as criminal toxicology)

This is when biological samples from a living person are analysed. For example, in relation to assaults, drug assisted sexual assaults and road traffic offences. Toxicology can also help determine if a person was under the influence of a substance such as alcohol or drugs at the time they committed an offence. It is possible that this could have affected their behaviour and may even feature as part of their defence.

Recent changes to road traffic offences means that there are now legal limits for certain drugs. In other words, if a driver is found to have one of the drugs covered by the legislation over the legal limit, they are guilty of an offence. Toxicology departments provide the analysis of blood samples taken from drivers and prepare reports detailing the drugs(s) found, their concentrations and if they are above or below the legal limit.

Determining the Effects

The effects of drugs and alcohol depend on many different things. Each individual will respond differently following the ingestion of a drug or alcohol. Additionally, people will have different tolerances to drugs and alcohol depending on whether they are heavy drinkers, drug users or regularly taking a prescription drug. The variety of drugs and medicines available is vast. However, the majority of substances have published data that reports the likely effects and therapeutic and fatal ranges of concentrations. This information can help a toxicologist interpret their findings for the purpose of the report.

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 likely alcohol level would have been at the time of the crash, taking into consideration factors such as the height and weight of the accused.

When it comes to deciding how much alcohol you can consume 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.


Some of the techniques used to analyse samples include gas chromatography with mass spectrometry (GCMS), liquid chromatography with mass spectrometry (LCMS) and liquid chromatography with tandem mass spectrometry (LCMS/MS). More recent advances also include accurate mass spectrometry.

Once the analysis is complete a toxicologist will prepare a report for the Crown Office and Procurator Fiscal Service. The report will state the drug(s) found, the concentration (if available) and the likely effects these drug(s) will have had both on their own and in combination with other drugs.