Right Driver

Drug driving limits

Even though there are eight drugs listed under illicit drugs, traces of these drugs can be present if a person has been taking certain types of legally prescribed drugs. The limits are low enough to allow for these trace levels, but not to allow people to drive under the influence of drugs.

It is safe to assume that there is no way of calculating what kind of consumption of illicit drugs will put you over the limit, and therefore you should not consume any illicit drugs before driving – they all have a negative effect on your driving ability. The government has said that the levels are so low that even small doses will likely test positive.

For prescription drugs, doctors will advise how long you should wait after taking them until you can drive again, or the limits are set at levels that would accommodate normal usage of the drug.

Illicit drugs

These drugs are essentially zero tolerance.

  1. benzoylecgonine, 50 µg/L
  2. cocaine, 10 µg/L
  3. delta–9–tetrahydrocannabinol (cannabis and cannabinol), 2 µg/L
  4. ketamine, 20 µg/L
  5. lysergic acid diethylamide (LSD), 1 µg/L
  6. methylamphetamine, 10 µg/L
  7. methylenedioxymethaphetamine (MDMA – ecstasy), 10 µg/L
  8. 6-monoacetylmorphine (6-MAM – heroin and diamorphine), 5 µg/L

Prescription drugs

These drugs have the potential to be abused, but under normal prescription levels will not exceed these limits.

  1. clonazepam, 50 µg/L
  2. diazepam, 550 µg/L
  3. flunitrazepam, 300 µg/L
  4. lorazepam, 100 µg/L
  5. methadone, 500 µg/L
  6. morphine, 80 µg/L
  7. oxazepam, 300 µg/L
  8. temazepam, 1000 µg/L

Amphetamines have not been given a threshold yet because the government decided that proposed limits needed to be reconsidered so that those taking medication for attention deficit hyperactivity disorder are not affected.

The government has asked pharmacies to help customers understand the new rules. There are posters and leaflets available.

Screening process and statutory medical defence

Since 1988 it has been illegal to drive while impaired by drugs – this was outlined in section 4 of the Road Traffic Act 1988. Section 5A was amended in April 2013 to add a new offence of driving whilst impaired through drugs above specific limits, which removes the ambiguity of the previous law.

Roadside saliva tests will be used to quickly identify if a person has been using one of the drugs listed above, or one that will metabolise into one of the drugs. If the saliva test is positive, the person will then be requested to provide a blood sample for evidential purposes, and this will be used if a prosecution is sought.

If a person is using medication that has been prescribed then they can raise the statutory ‘medical defence’ at any stage. There are some cases where a high dosage will be prescribed that will put a person over the limit, but this is likely to be a small number. The medical defence can be raised if the drug was lawfully prescribed, supplied or purchased over-the-counter, for medical or dental purposes; and the drug was taken in accordance with advice given by the person who prescribed or supplied the drug, and in accordance with any accompanying written instructions (so far as the latter are consistent with any advice of the prescriber).


Darren has owned several companies in the automotive, advertising and education industries. He has run driving theory educational websites since 2010.

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