A new test known as the Drugalyser® is due to be introduced into police traffic proceedings in the coming year, to help police detect and tackle drug-driving offences at the roadside. With this in mind, Evans Halshaw provides this guide to how different drugs can affect your driving ability - and why you shouldn't get behind the wheel if you're under the influence.



This guide will take you through the causes and effects of drug-driving, from how you behave on the road to how your brain and neuron functions are affected. Switch drugs using the tab on the left, and use the tab on the right to switch between your car and your brain. Hover over the blue circles for an in-depth look at what each drug does to alter your perceptions and behaviour.

Drugalyser® is a registered trademark of Modern Health Systems (MHS) Ltd. This guide is produced by Evans Halshaw and has no connection with MHS Ltd or any other organisation.

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Cannabis can affect attention span and reaction times, as well as eye-tracking abilities, making drivers under the influence almost twice as likely to cause a road accident.


Interference with short-term memory; inhibited coordination and speech; altered "high" consciousness. In large doses can cause delusions and hallucinations.


Poor spatial awareness and coordination; slower reactions to sensory input; less accurate actions.


Impaired muscle movements; involuntary reactions; altered emotional reactions and anxieties. Long-term use can affect learning ability.


Part of the limbic system, responsible for transferring short-term memories into long-term memories and controlling spatial navigation.


Plays a role in motor control, managing coordination, precise actions and timing.

Basal Ganglia

A cluster of neurons responsible for a number of functions including movement, learning ability and emotional reaction.

Pre-frontal cortex

Thought to be where cognitive performance is controlled, including decision-making and social behaviour.

Temporal lobe

Involved in retaining visual memory, processing sensory information and understanding language and meaning.

Blood vessels

Supply brain with oxygen and nutrients via blood stream.

Cerebral Cortex

The outermost layer of the brain, connected to various important outer sections responsible for processing sensory information.

Locus Ceruleus

Part of a system which controls physical and chemical reactions to novelty and excitement, as well as panic and stress.

Raphe Nuclei

Cluster of cells and neurons responsible for the regulation of pain and the release of serotonin to the rest of the brain.


Cannabis increases the user's sensory awareness, which in some cases can cause over-reaction, anxiety and panic attacks. Users may also suffer blackout memory loss, and prolonged issues with short-term memory.


Cocaine's long-term effects on the brain are significant, causing rapid ageing and an inability to cope with basic processes efficiently. These effects can become permanent.


The main side-effects of LSD are distorted senses and hallucinations - users are likely to see warping and colour-changing, and many find they lose sense of the passage of time. Generally speaking LSD will heighten the mood the user is already in, and can often cause anxiety and panic attacks.

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