Tougher controls are needed on the popular hormone melatonin, sold in health shops as a food supplement, according to an expert.
University of Hong Kong professor Pang Shiu-fun, who has studied melatonin for 30 years, said a lack of controls meant people took risks when dosing themselves with the readily available pills.
Melatonin, introduced to Hong Kong in the past three years, is used by health workers, pilots and other shift workers to regulate sleep patterns.
But Government Chief Pharmacist Anthony Chan Wing-kin said although vitamins and hormones had to be registered, melatonin was exempt from the checks on manufacturing, analysis and labelling requirements.
'Melatonin is a unique hormone. It has not been proven to be medicinally effective,' Mr Chan said.
'It only came to Hong Kong two or three years ago and, at that time, we considered whether it should be controlled as a drug like other hormones.' A study of scientific literature had found no dangerous side effects and analysis of some brands of melatonin had raised no concern, Mr Chan said.
But Professor Pang said worrying side effects were coming to light and called for checks on the quality and labelling of melatonin sold here.