Postmarketing surveillance and adverse drug reactions: current perspectives and future needs.

Spontaneous reporting systems like MEDWATCH can be effective in revealing unusual or rare adverse events that occur with the use of medications, and such reports may often be sufficient to assign causality. However, spontaneous reports do not reliably detect adverse drug reactions (ADRs) that occur widely separated in time from the original use of the drug or that represent an increased risk of an adverse event that occurs commonly in populations not exposed to the drug. In these situations, spontaneous reports alone do not provide sufficient evidence to conclude that the adverse event was an ADR. Identification of ADRs associated with long-term administration of drugs for chronic diseases also remains problematic. Methods to evaluate ADRs using data from clinical trials, medical records, and computerized databases of medication users and nonusers must be developed to complement spontaneous reporting systems. Without these methods, potentially important ADRs will remain undetected, and spurious associations between adverse outcomes and medications or devices will remain unchallenged.