Essential medicines, as defined by the World Health Organization are "those drugs that satisfy the health care needs of the majority of the population; they should therefore be available at all times in adequate amounts and in appropriate dosage forms, at a price the community can afford."

The WHO has published a model list of essential medicines. Each country is encouraged to prepare their own lists taking into consideration local priorities. At present over 150 countries have published an official essential medicines list. The WHO List contains a core list and a complementary list.

The core list presents a list of minimum medicine needs for a basic health care system, listing the most efficacious, safe and cost-effective medicines for priority conditions. Priority conditions are selected on the basis of current and estimated future public health relevance, and potential for safe and cost-effective treatment.

The complementary list presents essential medicines for priority diseases, for which specialized diagnostic or monitoring facilities are needed. In case of doubt medicines may also be listed as complementary on the basis of consistent higher costs or less attractive cost-effectiveness in a variety of settings.

The compilation of an essential medicines list enables health authorities, especially in developing countries, to optimize pharmaceutical resources.

The list is important because:

• it forms the basis of national drugs policy in many countries, both developed and developing (e.g. South Africa, Eritrea).
• governments refer to WHO recommendations when making decisions on health spending.