Researchers are developing vaccines which might one day help nicotine and cocaine addicts quit their habits, the British Association science festival heard yesterday.

Addicts might find it easier to cope with their withdrawal if they found that their drug no longer delivered a rush of euphoria, immunologist Campbell Bunce told the gathering in Salford.

Vaccines trigger the immune system to produce antibodies or natural agents that block invasive infection. Dr Bunce, of Xenova Research at Cambridge, said he and colleagues had managed to produce a "fairly strong antibody response to both nicotine and cocaine".

The more antibodies in circulation within the body, the more effective the strategy. Preliminary trials had offered encouragement and new trials on vaccines for both drugs were due to begin shortly.

"With the cocaine vaccine we are, hopefully, going to try to establish how effective that vaccine is at helping people give up cocaine. With the nicotine vaccine trial we want to look at the optimum dose, the best dosing regimen to improve the production of antibodies."

Through associated diseases such as heart disease and cancer, nicotine addiction killed 4 million adults in 2000. But tobacco directly affects heart rate and reduces skin temperature. Researchers will vaccinate their human guinea pigs and then offer them a cigarette, then measure heartbeat and skin temperature to see whether the antibodies have blocked the drug's journey to the brain.

"We are making progress and certainly how successful or how efficacious we are going to be is a little way down the line," Dr Bunce said.

"Certainly we are not the only company interested in generating these vaccines, which gives an idea of how seriously people are taking this concept."

The researchers do not expect the vaccines to help addicts overcome the raw cravings for nicotine, or help with the anxiety or depression that accompany withdrawal. The antibody response is more likely to help prevent relapse in those who have decided to give up.

No non-user has been vaccinated in the trials of cocaine vaccine. The cocaine addicts in the trial were otherwise healthy individuals who were increasing their risk of seizures, heart attack, hallucinations and paranoia. Volunteers came from counselling services.

Most of the people treated with a nicotine vaccine were smokers, but the first safety trials included a group of nonsmokers. In future, he said, parents might wish their adolescent children to be protected against a drug-taking habit.

"That is something that has ethical implications - but it is something to consider," he said.

Tests have yet to measure the impact of the nicotine vaccine on the "rush" from a cigarette.

But cocaine addicts reported that the immunisation delivered a reduced sense of euphoria. "These antibodies did seem to have an impact on the overall sensation they were feeling," he said.