Drug driving and medicine: advice for healthcare professionals

Information to help healthcare professionals understand changes to drug driving laws and what this means for patients.

Drug limits

The drug driving offence, enforced from 21 October 2019, covers 17 controlled drugs.

The drugs fall broadly into two groups.

Zero tolerance group

This group consists of commonly abused drugs for which very low limits have been set. It includes certain medicines that will be taken by only a small proportion of drivers.

Given the low limits set, a patient prescribed one of these medicines who chooses to drive could test above the specified limit but would still be entitled to raise the statutory 'medical defence'.

Drug Threshold limit in microgrammes per litre of blood (µg/L) 
benzoylecgonine 50μg/L
cocaine 10μg/L
delta-9-tetrahydrocannibinol (cannabis) 2μg/L
ketamine 20μg/L
lysergic acid diethylamide (LSD) 1μg/L
methylamphetamine 10μg/L
methylenedioxymethamphetamine (MDMA) 10μg/L
6-monoacetylmorphine (heroin) 5μg/L

Road Safety Group

This group consists of mainly licensed medicines that have a significant liability to be abused, and for which the specified limits have been set at a higher level than the first group, at the point where significant impairment to driving becomes evident.

The higher limits are generally above the normal therapeutic range so most patients are unlikely to be driving with a concentration of a specified drug in their body above the specified limit.

However, those on particularly high doses, for example, could test above the specified limit and where that happens they would  be entitled to raise the statutory medical defence.

Drug Threshold limit in microgrammes per litre of blood (µg/L) 
clonazepam 50μg/L
diazepam 550μg/L
flunitrazepam (no longer licensed in the UK) 300μg/L
lorazepam 100μg/L
oxazepam 300μg/L
temazepam 1,000μg/L
methadone 500μg/L
morphine 80μg/L

A separate approach for amphetamine

amphetamine                                   250μg/L

Amphetamine is also included as a specified controlled drug for the purpose of the new offence.  An approach balancing risk has been adopted in recognition of the fact amphetamines are illegal but can also have a medicinal use.

The statutory 'medical defence' can be raised by patients taking medicines in accordance with instructions from either of the above groups.

Information on whether any particular medicine is affected by the new legislation can be found in the summary of product characteristics for that medicine.

See: The Drug Driving (Specified Limits) (Scotland) Regulations 2019












Email: ceu@gov.scot

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