Essential drugs are those 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 the appropriate dosage forms, and at a price that individuals and the community can afford. This concept is intended to be flexible and adaptable to many different situations; exactly which drugs are regarded as essential remains a national responsibility.

Model lists have proved to be invaluable in improving the quality of health care and reducing costs (3, 4). Better quality of care is achieved when the list of essential drugs is linked to evidence-based treatment guidelines (5), especially when the supply system guarantees the availability of the selected drugs. Treatment guidelines can also focus training and serve as a standard for supervision and medical audit; prescribers become more familiar with the drugs and can better recognize adverse drug reactions. Lower costs are achieved through selecting cost-effective treatment. A limited range of drugs in the supply system may lead to economies of scale and competition between manufacturers, further reducing the costs.

Market approval of a pharmaceutical product is usually granted on the basis of efficacy, safety and quality and rarely on the basis of a comparison with other products already on the market, or cost. However, in some developing and most developed countries the majority of drug costs are covered by public funds or through health insurance schemes. Most public drug procurement and insurance schemes have mechanisms to limit procurement or reimbursement of drug costs. An evaluation process is therefore necessary, based on a comparison between various drug products and on cost/benefit considerations. The advantage of a new treatment over the existing one is then compared to its extra cost. Such information has proved very helpful in taking informed decisions about the selection of essential drugs. The model list is intended to help with this evaluation.