IT IS being billed as a magic potion that helps Chinese athletes smash world records and Hong Kong lovers improve their athletic performances. But Hong Kong experts say the worm-based drink which has made headlines around the world is neither a wonder drug nor an aphrodisiac - just a nourishing health tonic. Local Chinese medicine practitioners warn people using dongchong xiacao - or winter-worm summer grass - to enhance their performances will be disappointed. They say there is no direct link between the drink and the recent record-breaking spree by mainland female athletes. Coach Ma Junren amazed the world by claiming his record-breaking athletes, led by Wang Junxia, were helped by a special diet that included the worm drink. His runners broke three world records in five days at the Seventh National Games in Beijing. ''Perhaps the athlete would feel vigorous after taking the potion, but I don't think the worms would enhance their physical strength,'' said Yu Wui, chairman of the Association of Hong Kong and Kowloon Practitioners of Chinese Medicine. ''You cannot take a lot of these worms today and then run faster tomorrow,'' said Lin Shu-ling, the head of the Society of Practitioners of Chinese Herbal Medicine. The supervisor of the Kowloon Society of Practitioners of Chinese Medicine, Tsoi Sheung-Bun, said he did not think drinking the potion would directly help athletes build up muscle strength. Mr Tsoi said some people had misunderstood that dongchong xiacao could be used as an aphrodisiac. ''A lot of people think that anything good for the kidneys is an aphrodisiac, but it's not true,'' he said. The worms are also used to ease lung complaints and tuberculosis. They do not come cheap. Prices vary from between $700 to $4,000 a catty depending on the quality.