EVERY day at least 3,000 Hongkong people take a small yellow pill, hoping that within the next eight days, their memory will be improved, mental alertness sharpened and cerebral functions heightened. The pill, Craton, was introduced to Hongkong in November last year: in the past five weeks, more than 3,000 packets of 30 pills have been sold - at a cost of $140 a packet - to people who are hoping to slow the ageing process, prevent premature senility or become smarter. Thousands of others are consuming ginseng and taking an assortment of other supplements and vitamins for the same purpose. But whether or not you can enhance brain power and improve concentration by taking herbal extracts and vitamins is a bone of contention among medical practitioners, who say there is ''no proof'' these treatments work. Craton, a controversial German-made pill recognised by the German health authorities and registered in Europe, North America and the US as a drug, does not have to be registered in Hongkong because it falls under the category of Chinese herbs. The company behind the pill, Boehringer Mannheim China Ltd, says the sales speak for themselves. Managing director Mr Patrick Chiu, a registered pharmacist, said the pills were made from extracts of the gingko plant. The extracts contain flavone gycosides, which are said to remove free radicals in the body. Mr Chiu said Craton worked indirectly on the brain by increasing blood circulation. ''Studies have shown that in people over the age of 30, blood circulation to the brain gradually slows down,'' Mr Chiu said. ''Herbal medicines help to increase circulation and activate nerve cells in the brain.'' But, a leading neurologist said there was no solid evidence to support claims that gingko could improve a person's well-being, because no large-scale clinical studies had been done. He said thousands of patients would need to be studied to prove the claims. ''There is no drug that treats dementia, mental deficiencies or cerebral insufficiencies at the moment and preventative drugs are even more out of the question,'' he said. ''Some people may like to take vitamins because it gives them a placebo effect. Itprobably won't do any harm provided they don't take too much, but there is no evidence from a scientific point of view and I certainly won't recommend it for my own patients.'' The product has been sold in Europe for a number of years and, according to Mr Chiu, no side effects have been reported. But a spokesman for the Hongkong Medical Association, Dr Lee Kin-hung, said: ''Among the profession, we don't believe any foodstuff can enhance brain power. As far as we can see there is no proof that this works. ''Herbal medicine has not been scientifically tested enough, and although the number of side effects reported generally is small, this is not the sort of thing we would encourage people to take blindly. ''I wish there was something we could do to help people enhance brain power, but there isn't. Nothing can stop the degenerative process.'' But the resistance of medical practitioners to accept vitamins and other intellect-enhancing drugs has done little to stem the tide of similar products in Hongkong. A former computer executive, Mr Marshall Gabin, is hoping to introduce a US-made range called Life Services Supplements to Hongkong. Although doctors in the US frequently recommend such supplements, Mr Gabin said no studies had been done on the effects of the products. Anti-oxidants in the supplements are supposed to soak up free radicals in the body. Mr Gabin said Hongkong was an ''immature market'' given the lack of understanding of brain-enhancing pills. ''In Hongkong there seems to be a bias among the medical profession against supplements,'' he said. ''They think that if you eat a balanced Chinese diet that's all you need. ''It is going to take them a while to understand.'' Professor Kwan Chiu-yin, head of the department of physiology at the University of Hongkong, said ginseng was often used to help prevent memory loss. ''Certain substances are known to enhance will, determination and concentration, but it is not easy to scientifically measure the effects,'' he said. ''In China, people use qi gong to help release hormones through meditation which achieve the same effect. Enough improved circulation will give a better supply of oxygen through the body and this will help you feel better. ''A lot of herbal recipes in Chinese medicine work on the cardio-vascular system and improve the blood flow . . . and this in turn improves awareness and concentration. ''So if vitamins and other pills work, I think it is because of the indirect action on the brain. Whether there is any direct action remains to be seen.''