On Essentiality and the World Health Organization's Model List of Essential Medicines.

BACKGROUND: In 1977 the World Health Organization created its first Model List of Essential Medicines-a list designed to aid countries in determining which medicines to prioritize on their National Essential Medicines Lists. In classifying drugs as "essential," the World Health Organization has historically stressed drugs' ability to meet priority health needs of populations and cost.

OBJECTIVES: In this paper we trace the fluctuations in the application of cost and priority status of disease as criteria for essential medicines throughout the reports published by the WHO Expert Committee on Selection and Use of Essential Medicines since 1977.

METHODS: We analyzed essential medicines lists published on the World Health Organization website since 1977 for trends in criteria concerning cost and priority status of disease. Where, available, analyzed the World Health Organization Expert Committee analysis rationalizing why certain medicines were or were not added and were or were not removed.

RESULTS: The application of the criteria of cost and priority status of essential medicines has fluctuated dramatically over the years.

CONCLUSIONS: The definition of essential medicines has shifted and now necessitates a new consensus on normative definitions and criteria. A more standardized and transparent set of procedures for choosing essential medicines is required.