Adverse drug reactions: scope and limitations of causality assessment and the use of algorithms.

Deciding whether a drug caused a particular unwanted event in a given patient, or at least what degree of probability attaches to the association, is a medically important issue. The elements in the case history which are most likely to determine the conclusion are well known and they are often employed instinctively by the experienced physician. It can be helpful to draw up a checklist of the factors to be borne in mind, and some workers have gone so far as to develop algorithms and apply mathematical principles to the issue Algorithms can be helpful in the individual patient but they are probably more trouble than they are worth if used routinely.