The list is divided into core items and complementary items. The core items are deemed to be the most cost effective options for key health problems and are usable with little additional health care resources. The complementary items either require additional infrastructure such as specially trained health care providers or diagnostic equipment or have a lower cost-benefit ratio. About 25% of items are in the complementary list. Some medications are listed as both core and complementary. While most medications on the list are available as generic products, being under patent does not exclude inclusion.
The first list was published in 1977 and included 212 medications. The WHO updates the list every two years. The 14th list was published in 2005 and contained 306 medications. In 2015 the 19th edition of the list was published and contains around 410 medications. The 20th edition was published in 2017. The national lists contain between 334 and 580 medications.
A separate list for children up to 12 years of age, known as the WHO Model List of Essential Medicines for Children (EMLc), was created in 2007 and is in its 5th edition. It was created to make sure that the needs of children were systematically considered such as availability of proper formulations. Everything in the children's list is also included in the main list.