Changes in the World Health Organisation essential drug list.

The World Health Organisation Model List of Essential Drugs is an attempt to provide guidelines for selection of essential pharmaceuticals. Analysis of the six lists produced between 1977 and 1990 shows an increase in the number of items from 205 to 268. 120 drugs have been added and 57 deleted; however, only 16 of the additional drugs can be considered new clinical entities or to have new indications. The original purpose of the essential drug list was to itemise the minimum number of essential drugs. Many additions were due to a change in perception about the usefulness of a particular drug, not scientific advances. Nevertheless, the list remains a useful guide for countries selecting their own national lists.