This study examined the composition of over-the-counter (OTC) sleeping pills in Hong Kong and reviewed the current knowledge about the hypnotic efficacy and safety of their major herbal and dietary supplement constituents. We conducted a cross-sectional survey of OTC sleep aids at drug stores in a residential district of 0.3 million population and literature search using MEDLINE, EMBASE, PsycINFO, China Journal Net, China Biomedical Database and relevant English and Chinese literature. We identified 17 brands of OTC sleeping pill: eleven of them were composed of mixtures of Chinese and Western herbal agents and six brands contained 3 mg of melatonin. The Chinese herbal mixture suanzaorentang, comprising zizyphi spinosi semen, poria cocos, ligusticum wallichii, anemarrhenae rhizoma and glycyrrhizae radix in ratio of 7:5:2:1:1, was the most common OTC sleeping pill available in the survey. Our literature review showed that kava, valerian and melatonin were the better-researched herbs and dietary supplements, however, the data on hypnotic efficacy and safety was inadequate to support their clinical use. More rigorous investigations of the risk-benefit relationship of herbal agents and dietary supplements used for insomnia are needed.