patient's subjective assessment of its effects. Causal relationship is said to exist when a drug is thought to have caused or contributed to the occurrence of an adverse drug reaction. Clinical trial (or study) refers to an organised program to determine the safety and/or efficacy of a drug (or drugs) in patients. The design of a clinical trial will depend on the drug and the phase of its development. Control group is a group (or cohort) of individual patients that is used as a standard of comparison within a clinical trial. The control group may be taking a placebo (where no active drug is given) or where a different active drug is given as a comparator. Dechallenge and rechallenge refer to a drug being stopped and restarted in a patient, respectively. A positive dechallenge has occurred, for example, when an adverse event abates or resolves completely following the drug's discontinuation. A positive rechallenge has occurred when the adverse event re-occurs after the drug is restarted. Dechallenge and rechallenge play an important role in determining whether a causal relationship between an event and a drug exists. Effectiveness is the extent to which a drug works under real world circumstances, i.e., clinical practice. Efficacy is the extent to which a drug works under ideal circumstances, i.e., in clinical trials. Event refers to an adverse event. Harm is the nature and extent of the actual damage that could be or has been caused. Implied causality refers to spontaneously reported AE cases where the causality is always presumed to be positive unless the reporter states otherwise. Individual Case Safety Report is an adverse event report for an individual patient. Life-threatening refers to an adverse event that places a patient at the immediate risk of death. Phase refers to the four phases of clinical research and development: I – small safety trials early on in a drug's development; II – medium-sized trials for both safety and efficacy; III – large trials, which includes key (or so-called "pivotal") trials; IV – large, post-marketing trials, typically for safety reasons. There are also intermediate phases designated by an "a" or "b", e.g. Phase IIb. Risk is the probability of harm being caused, usually expressed as a percent or ratio of the treated population. Risk factor is an attribute of a patient that may predispose, or increase the risk, of that patient developing an event that may or may