GPs in East Sussex handed over responsibility to specialist nurses for the government drive to encourage more people to kick the smoking habit. But they have been told that only family doctors should prescribe the drug locally, because they alone have full medical histories of patients, a move potentially damaging to attempts to create more all-in anti-smoking clinics.

It is understood that some doctors might now refuse to issue prescriptions for Zyban. They believe the specialist nurses had operated a successful service, partly because they had been able to devote time to patients. In addition, some GPs argue that the extra referral back to them implies safety question marks over the drug. They also fear they will be put under pressure by patients who think they are entitled to the drug.

The decision to ban nurses prescribing Zyban, by managers of the Sussex Downs and Weald primary care trust, runs counter to the government's guidance. This favours one-stop shops, where advice, counselling and prescription of both nicotine replacement therapies, such as inhalers, patches, gums and lozenges, and Zyban, are available from one centre.

But few such arrangements, known as patient group directions, for Zyban are in place. The trust said it would be monitoring whether patients complained at the new arrangements, which had been changed "in view of concerns raised about Zyban". The drug would not be prescribed by smoking cessation services "until those issues of concern were resolved".

The Department of Health, which has no idea exactly how many patient group directions there are, is seeking to stay out of the row, saying it is up to local managers to decide, provided patients have access to a range of treatments. A spokeswoman added it would be misleading to claim that a local decision on Zyban undermined the success of smoking cessation clinics or the principle of the one-stop shop.

Zyban was licensed in Britain in 2000 and its use as an effective treatment was endorsed right across the NHS in March this year. Prescribers are warned that people under 18, pregnant women, breastfeeding mothers and people who might be at risk of seizures should not take it.

Medicine watchdogs have been told of 7,866 reports of suspected "adverse reactions", 63 of which have had a fatal outcome. The Department of Health says this should be seen in the context of widespread use, 540,000 individuals up to March 2002.

"In the majority of these cases, the individual's underlying condition may provide an alternative explanation."

Disorders of the heart, brain and blood vessels, including strokes, were the reported cause of death in 70% of them. "A Europe-wide review of the safety of Zyban concluded in July that the balance of risks and benefits for Zyban as an aid to smoking cessation remains favourable."