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Drugs & Driving

We make 80% of all our journeys by car. Telling someone they cannot drive is serious. Not just the patient may be affected; others in the house may rely on the patient for their transport. Recent BMJ correspondence looked at the diseases which may impair fitness to drive. Another worry is prescribing drugs which impair fitness. One study of deaths in road traffic accidents found tricyclic antidepressants in body fluids of 0.2% of victims, compared with alcohol (35%) or other drugs likely to affect the CNS (7.4%) [1].

Morphine and driving

Reassuring results have come from a Finnish study of driving ability in cancer patients taking long-term morphine [2]. Although morphine given as a single dose to a healthy volunteer impairs reaction time, co-ordination, attention and memory, this is not true for patients on long-term stable doses.

The authors used a battery of tests designed for professional drivers (Austrian Road Safety Board - as used for Helsinki bus drivers) to compare the performance of 24 patients on continuous morphine (mean 210 mg oral morphine daily) with that of 25 pain-free patients who took no regular analgesics. The morphine patients had been on a stable dose (twice daily sustained release formulation) for at least two weeks.

There was no significant difference between the morphine patients and the controls on the driving simulator tests. Balancing ability with eyes closed was significantly worse with morphine, finger-tapping with preferred hand was better. The conclusion was that patients on long-term stable dosing with morphine should be at no greater risk to themselves or to other road-users.

Changing the dose

How long should drivers taking morphine stay off the road after changing dose? Perhaps the best information comes from a study [3] which suggested that an increase in the dose by 30% will impair cognitive function for one week after the increase. The study indicated that at least the first 3-5 days may be "impaired". It might be safe to use this time limit in the absence of more conclusive evidence.


  1. JT Everest, RJ Tunbridge, B Widdop. The incidence of drugs in road accident fatalities. Crowthorne: Transport Research Laboratory, 1989. (TRL research report 202)
  2. A Vainio, J Ollila, E Matikainen, P Rosenberg, E Kalso. Driving ability in cancer patients receiving long-term morphine analgesia. Lancet 1995 346: 667-70.
  3. E Bruera, K Macmillan, J Hanson, RN MacDonald. The cognitive effects of the administration of narcotic analgesics in patients with cancer pain. Pain 1989 39: 13-16.

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