The popularity of Chinese herbal medicines (CHMs) demands a critical analysis of safety issues. The aim of this systematic review is to summarize data regarding adulterations of CHMs with conventional drugs. Literature searches were carried out in six databases. Articles containing original data on adulterations were considered without language restrictions. Eighteen case reports, two case series and four analytical investigations were identified. The list of adulterants contains drugs associated with serious adverse effects like corticosteroids. In several instances, patients were seriously harmed. One report from Taiwan suggests that 24% of all samples were contaminated with at least one conventional pharmacological compound. It is concluded that adulteration of CHMs with synthetic drugs is a potentially serious problem which needs to be addressed by adequate regulatory measures.