Experts are developing drugs that copy the active ingredients in tobacco that stimulate the brain without causing heart disease, cancer, stroke or addiction.

The move follows the discovery that nicotine can boost the intelligence and recall ability of animals in laboratory experiments.

The researchers, who present their latest findings at a brain conference today, hope that the new drugs, which will be available in five years, could have fewer side effects than existing medicines for dementia.

But they stress the new treatment would not be a cure for Alzheimer’s disease. At best it will only give patients a few extra months of independent life.

Tobacco has long been known to have a stimulating effect on the brain. Victorian doctors recommended smoking as a means of sharpening the wits and boosting concentration.

However, the deadly side effects of cancer, stroke and heart disease, mean its benefits have been neglected by medical research.

Professor Ian Stoleman, from the Institute of Psychiatry, King’s College, London, has shown that nicotine can improve the performance of rats in an intelligence and memory test.

“The substances that we call drugs have, in the majority of cases, do have a mixture of beneficial and harmful effects and nicotine  no exception to this,” he said.

“When we started this work 10 years ago we didn’t think that we would find beneficial effects on cognitive performance on normal subjects.

“But we were able to find an effect in the sense of the acute administration of nicotine producing small improvements in performance of tasks in normal rats.”

His team trained rats to respond to a brief flash of light by standing in an area of a cage. If they moved to the right spot, they were rewarded with a food pellet.

After they mastered the task, the rats responded correctly around 80 per cent of the time. But after being injected with nicotine, the success rate went up 5 per cent.

The difference was much starker when the rats were distracted with loud noises. Then they got the task right 50 per cent of the time without nicotine – but 80 per cent of the time with it.

Prof Stolerman’s team have studied how nicotine alters the brain’s circuitry to boost memory and concentration – and identified some of key brain receptors and chemical messengers – such as dopamine and glutamate – that are involved.

They also found differences in the chain of events that leads to boosted brain power – and the chain of events that leads to addiction.

“We believe that by building on these differences it may be possible for medicinal chemists to devise compounds that produce some of the beneficial effects of nicotine,” he said.

The findings are being presented today at the Forum of European Neuroscience in Geneva.

Drugs companies have been working for 10 to 15 years to develop compounds based on nicotine that produce only beneficial effects. The new discoveries could lead to a new drug – based on nicotine – within “a few years”.