In a development unlikely to reduce cigarette consumption but almost certain to produce other benefits — at least for male patients — a “computer glitch” led to smokers being mistakenly prescribed Viagra instead of the anti-smoking drug Zyban.

The problem is thought to have become apparent several weeks ago. About 900 family doctors at 300 surgeries have been sent an e-mail from NHS Greater Glasgow giving warning about a malfunction by its “e-Formulary” IT system, which automatically lists the most popular drugs when doctors fill out prescriptions. When GPs tried to select Zyban, a drug that suppresses the part of the brain that experiences nicotine cravings, the computer instead selected sildenafil, the generic name for Viagra, which is used to treat impotence.

In a statement yesterday, Greater Glasgow NHS said that patient care had not been impaired by the blunder because prescriptions were “subject to stringent double-checking by both prescribing doctors and pharmacy staff”.

A spokeswoman for the health authority said that no patients had complained of having been given Viagra in error. Although all surgeries in the area had been warned as a precaution, only two had reported the problem.

Family doctors, however, said taht it was unlikely that all prescription mistakes would have been noticed. One Glasgow doctor said: “In some cases, it’s possible that GPs will have spotted the problem after printing out a prescription. But some will not, and unsuspecting patients will have gone to the chemist's and unknowingly ordered Viagra.

"There is a chance the pharmacist would spot this, especially if it was a woman who handed in the prescription. But there would be no reason to double-check when a man handed it in."

Another GP said: "These are interesting drugs to get confused. Zyban was developed as an antidepressant and has a curious side-effect in that it reduces many patients’ urge to smoke. Viagra gives the urge to do something quite different."

Apart from tiredness there are thought to be few side-effects of Viagra, a blue diamond-shaped pill that looks very different from Zyban, which is small and white.

Greater Glasgow NHS maintained a straight face about the mistake. It said: “A computer glitch was discovered by two Glasgow GP practices that use the Glasgow e-Formulary following a recent update of the online General Practice Administration System for Scotland (GPASS). As a precaution, an advisory e-mail and memo was immediately issued to all the Glasgow practices which use GPASS and have installed the e-Formulary, to alert staff to the potential problem.”

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