Counterfeit, falsified and substandard medicines pose a serious threat to human health, particularly in poorer countries with weak regulatory mechanisms. But the relationship between combating counterfeit medicines, addressing safety, quality and efficacy issues and enforcing privately owned intellectual property rights has become controversial. There are concerns that a wider definition of "counterfeit" threatens the trade in generic medicines of assured quality on which many developing countries depend; and about the legitimacy of the International Medical Products Anti-Counterfeiting Taskforce (IMPACT), the detention of generic drugs in transit in the European Union, and the negotiation of the Anti-Counterfeiting Trade Agreement (ACTA). "Counterfeit" has a specific meaning in intellectual property, related to willful trademark violations. But in relation to medicines it is now sometimes used in a much broader sense to do with misrepresentation of identity or source, or even medicines that are simply "substandard". Some countries use the term "falsified" to describe medicines that misrepresent their identity or source, but do not necessarily violate intellectual property rights. "Substandard" medicines are those that do not meet quality standards specified for them, but may also be defined specifically to cover products from authorized manufacturers which fail to meet quality standards set for them. Failure to reach agreement on the definitions of counterfeit, falsified and substandard medicines hampers the constructive policy debate and collaboration at the international level that are necessary to take effective action against the producers and distributors of these medicines.