Almost 800 adverse reactions to the anti-smoking drug Zyban have been reported since February 1 when the drug became available under the Pharmaceutical Benefits Scheme.

The reactions, including rash, anxiety, hives, hyperactivity, nausea and insomnia, were reported in the current issue of the Medical Journal of Australia by Elizabeth Benson, director of immunopathology at Sydney's Westmead Hospital.

Between February and mid-May the Australian Adverse Drug Reactions Advisory Committee had received 780 reports of adverse reactions to Zyban.

Dr Benson said some people's reactions were so severe they needed a period in hospital. But overall reactions were typical of those expected from the drug, of which the active ingredient is bupropion, she said.

Dr Benson said although the number of adverse reactions was high, it was proportional to the number of Australians using the drug and similar to that seen in other countries.

Last month The Age reported that health authorities were investigating the deaths of nine Australians to find out if Zyban contributed. The investigation is continuing. By the end of March more than 213,000 Australian smokers had tried Zyban, which helps to reduce nicotine cravings. "There's been a huge take up of this drug, we've never seen it happen before," Dr Benson said. "The drug allocation for use in Australia in the first year was used in two days."

Because so many Australians were trying Zyban, relatively rare adverse effects such as rash, joint pain and fever typical of a hypersensitivity reaction were occurring commonly, Dr Benson said.

In one case, a 35-year-old patient taking Zyban visited his GP up to three times complaining of discomfort in his throat and a hives-like rash. The man was eventually taken to a hospital emergency department where he was admitted and treated with antihistamines.

"The doctor had not worked out that the complaints were due to Zyban," Dr Benson said. The man's case showed that all doctors prescribing bupropion should discuss the risk of a hypersensitivity reaction with their patients, she said.

The adverse effects with Zyban showed the importance of monitoring the effects of new drugs, especially those used by a large number of people in a short time frame, Dr Benson said.