Postmarketing surveillance (PMS) (also post market surveillance) is the practice of monitoring the safety of a pharmaceutical drug or medical device after it has been released on the market and is an important part of the science of pharmacovigilance. Since drugs are approved on the basis of clinical trials, which involve relatively small numbers of people who have been selected for this purpose - meaning that they normally do not have other medical conditions which may exist in the general population - postmarketing surveillance can further refine, or confirm or deny, the safety of a drug after it is used in the general population by large numbers of people who have a wide variety of medical conditions.
Postmarketing surveillance uses a number of approaches to monitor the safety of licensed drugs, including spontaneous reporting databases, prescription event monitoring, electronic health records, patient registries and record linkage between health databases. These data are reviewed to highlight potential safety concerns in a process known as data mining.
Canada: Health Canada is the regulatory body which approves drugs, and it has a division called "Marketed Health Products Directorate" (MHPD) which coordinates Canadian postmarketing surveillance. 
United Kingdom: The Medicines and Healthcare products Regulatory Agency (MHRA) and the Commission on Human Medicines (CHM) jointly operate the Yellow Card Scheme, which was one of the first examples of a Pharmacovigilance scheme, aimed at mitigating Adverse Drug Reactions (ADRs)
United States: Postmarketing surveillance is overseen by the Food and Drug Administration (FDA), which operates a system called MedWatch, to which doctors or the general public can voluntarily report adverse reactions to drugs.
- McNeil JJ, Piccenna L, Ronaldson K, et al. (2010). "The Value of Patient-Centred Registries in Phase IV Drug Surveillance". Pharm Med 24 (5): 281–288. doi:10.1007/bf03256826.
- "Post-marketing Pharmacosurveillance in Canada". Health Canada. 2005. Retrieved 2010-07-27.
- "Post-marketing Surveillance". U.S. FDA/CDER. 2004.
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