WHO's Essential Medicines

Every two years since 1977, the World Health Organization (WHO) publishes a list of medicines which are deemed essential and in order to attain the organization's goal of ensuring universal access to healthcare and medicines.
The list provides a minimum number of medicines for a basic health-care system. It is based on a medicine's efficacy, safe and cost-effectiveness for priority diseases of a given area or population.

 Source: WHO Model Lists of Essential Medicines