Which of the following is TRUE about an 'essential drug'?

Essential drugs are defined by the World Health Organization as those that satisfy the health care needs of the majority of the population and that therefore should be available at all times in adequate amounts and in the appropriate dosage and forms. The criteria of essential drugs includes established efficacy and safety, coverage of the majority of the diseases prevalent in the population, adequate quality, and stability. The selection of essential drugs also considers the the total cost of the treatment, changes in public health priority, and levels of health priorities. Ref: Policy Tools for Allocative Efficiency of Health Services: Xingzhu Liu By X Liu, 2003, Page 70; Essentials of Pharmacology by KD Tripathi, 6th edition, Page 5.