In your editorial on the medical use of cannabis (14 November, p 3) you wrote "Doctors in Britain have been allowed to prescribe heroin for people in chronic pain, yet there is no evidence that this heroin ends up on the black market."

"Have been" may be the nub of the statement. Back in the 1960s, I was able to prescribe Guinness for my elderly chronic bronchitics in Britain, but at about that time heroin was withdrawn from the pharmacopoeia for the very reasons you say there is no evidence for. There was also concern for the safety of the staff on wards where the drug was kept because intruders were apt to be violent in seeking out heroin.

The medical profession generally resented this change as heroin is a far more effective analgesic than morphine and doesn't produce intolerable nausea.

David Bolton Otago University Medical School Dunedin, New Zealand

- --- Checked-by: Rich O'Grady

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