What are the effects of drugs on driving?

Many drugs have an effect on driving. Some, such as alcohol and cannabis, can slow reaction times, reduce the ability to concentrate and distort the judgement of time and distance. Others, such as cocaine, may lead to people taking more risks. Prescription drugs too can affect our ability to drive.

The law

In 2012, the government announced a new offence in regard to driving with a specific controlled drug in the body above that drug’s accepted limit. In 2015 this law was updated to include a further 17 drugs (see the table below). It is now against the law to drive if:

  1. You have legal (including prescription) drugs in your body that have impaired your driving.
  2. You have ‘over the specified limits’ of illegal drugs in your blood, even if these do not appear to have affected your driving.

According to the UK Department for Transport guidelines on drugs and driving you should ask your doctor whether you can drive if you’ve been prescribed any of the following:

  • amphetamine, eg dexamphetamine or selegiline
  • clonazepam
  • diazepam
  • flunitrazepam
  • lorazepam
  • methadone
  • morphine or opiate and opioid-based drugs, eg codeine, tramadol or fentanyl
  • oxazepam
  • temazepam

You can drive after taking these drugs if:

  • you’ve been prescribed them and followed advice on how to take them by a healthcare professional
  • they aren’t causing you to be unfit to drive even if you’re above the specified limits.

Maximum blood levels of illegal and legal drugs from the Department of Transport


The blood levels given for illegal drugs are very low but were set at a level to rule out accidental exposure. Similar to drink driving, the police have a roadside test that makes it easier to detect those who are driving under the influence of illegal drugs. The Release website has a table with information about how long the drugs might remain in your system.


The penalties for drug driving are the same as for drink driving. If you are convicted you could face:

  • A minimum 12-month driving ban
  • A criminal record
  • An unlimited fine
  • Up to 6 months in prison
  • An endorsement on your driving license for 11 years

Updated January 2017


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