Some have serious side-effects and their use in healthy young people has not been investigated.
Suppliers of the so-called 'smart' drugs appear to be using a loophole in the Medicines Act which allows medicines to be imported for 'personal use'.
The Department of Health said last night it was 'very concerned' at the growing trade in these drugs, some of which were developed to treat age-related illnesses such as Alzheimer's and Parkinson's diseases.
'Their supply may be a contravention of the law and we are certainly taking urgent legal advice on the matter,' said a department spokeswoman. An advertisement for smart drugs placed by the Health Development Company in Cheltenham in last week's Time Out, the listings magazine, was 'almost certainly' outside the law and the department would be taking immediate action.
Medical experts also expressed concern about smart drugs. Dr Robert Howard, a lecturer in old age psychiatry at the Institute of Psychiatry, London, said: 'Some of the medicines are extremely toxic and should only be used under strict medical supervision.'
Roger Odd, of the Royal Pharmaceutical Society, said people who bought the drugs 'were playing with fire'.
But importers say the drugs can be legally obtained under Section 13 of the 1968 Medicine Act which allows their importation for personal use.
Stephen Cole, of HDC, said the drugs provided the ultimate high intelligence. 'We have 82 case studies involving thousands of people, including some children, which show no side-effects as such,' he said.
'This is remarkable when you consider if you gave eggs or cheese to that many people some would have a bad reaction.'
HDC customers are sent order forms, which go to Europe, where orders are made up.
HDC's range includes Hydergine, which is used to treat mental impairment in the elderly. Its side-effects can include blurred vision, nausea and vomiting. It is thought to improve memory and intelligence by mimicking chemicals that occur naturally in the brain. HDC charges pounds 15.84 for 30 tablets. Dr Howard said there was no evidence to show it could help young, fit people.
Vasopressin, another HDC drug, is used by doctors to replace a naturally occurring hormone that controls water loss by the kidneys. As a nasal spray it costs pounds 18.92 and is promoted as a physical and mental stimulant. The company cannot explain how it works, and it could cause health problems, doctors said.
Deprenyl tablets - promoted as 'life extension' pills by HDC at pounds 44.20 for 30 - are used in Parkinson's disease. Side-effects include low blood pressure, confusion or psychosis. Evidence that the drug can prolong life comes from studies in laboratory rats. Erythropoietin (EPO), a hormone that stimulates red blood cell production, is offered by HDC as 'sports nutrition'. It has been linked with sudden death in young professional cyclists.
Mike Dobson, HDC's pharmaceutical consultant, said he was sure the drugs were safe. 'I'm very worried that we are going to be branded as some kind of perverts who are supplying dangerous drugs, and this is not the case.'
Dr John Henry, of the National Poisons Information Service, a consultant physician who is quoted in HDC's information pack, said: 'I take great exception to being quoted in their letter. I've never talked directly to HDC, but I spoke to someone from a listings magazine about the drugs they advertised. I did tell her the drugs she listed were harmless, but I also said they wouldn't boost anybody's intelligence.'