Poor quality medicines have been described as a global pandemic that threatens the lives of millions of people. The problem is much more severe in poor-resource countries where pharmaceutical legislation and regulation are limited. Poor quality medicines are divided into three categories: substandard, degraded and falsified and the countermeasures vary according to each category. The use of poor quality medicine leads from minimal to severe complications (including death) for the individuals but also harms the community. Furthermore, they lead to a loss of confidence of the patients in essential medicines, in manufacturers and in health system and they increase the work burden for health workers, customs and police. To detect them, different techniques have been developed, each with advantages and limits. This article describes these aspects of poor quality medicines and also presents the factors that contribute to the existence and spread of poor quality medicines. A section of the article is devoted to the issue of poor quality medicine in Laos.