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Image of a eyeball showing the effects of cannabis/cocaine/ecstasy. Drug Driving. Your eyes will give you away. THINK! Search for 'drug drive'

Can the police test for drugs?

Drug drivers may think that just because they pass a test for alcohol they will be off the hook. This is not the case because the police can also prosecute a driver who is unfit through drugs and there are various ways they can detect and prove the offence.

One specific test the police may use is the Field Impairment Assessment (see below). It can be administered by trained officers at the roadside and is based on an observation of impairment, rather than a biological test. Police use five field impairment tests which are simple to complete if the person is not affected by any substance – but difficult if they are.

Watch the Field Impairment Assessment here

View the related YouTube video

Transcript for the Field Impairment Assessment (.doc, 21KB)

Before doing the FIA test, one of the first things the police can check is the effect drugs have on eyes. They have a pupil measure at their disposal if needed.

Image of an eyeball showing the effects of cannabis.

The most obvious effect of cannabis is that it causes the blood vessels in the eyes (and elsewhere) to become larger. The police will also notice a bloodshot appearance.

Image of an eyeball showing the effects of ecstasy.

Taking ecstasy significantly enlarges the size of pupils (mydriasis).

Image of an eyeball showing the effects of cocaine.

The short-term physiological effects of cocaine include constricted blood vessels and enlarged pupils.

All of these signs are obvious for the police to spot, but they are not the only thing that will give the drug driver away.

The five tests are:

  1. The Pupil Measure Test. Examination of the driver's eye pupil size, condition and reaction to light.
    An image of a pupil measurement card held up to a man's face
  2. The Romberg Test. This test assesses the subject’s balance and judgement of time. The subject is asked to tilt their head back slightly, close their eyes and estimate the passage of thirty seconds.
    An image of a man with his head tilted backwards
  3. The Walk and Turn Test. The subject must walk heel to toe along a straight line, counting their steps out loud and looking at their feet while doing so.
    An image of a man walking heel to toe
  4. The One Leg Stand Test. The subject must stand on one leg while counting out loud.
    An image of a man standing on one foot while balancing on the other
  5. The Finger to Nose Test. With the head tilted slightly backwards and eyes closed, the subject must touch the tip of their nose with the tip of their finger with the hand indicated by the officer.
    An image of a man placing his finger on his nose with closed eyes

If the police believe the driver was driving whilst unfit through drugs, they will arrest them at the roadside and take them down to the police station where they will be examined by a doctor, who can take a blood test.

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