‘Drugs as medicines’ highlights the principles behind the many success stories of using drugs to treat illness. Drugs can be used to cure or ameliorate the symptoms of many illnesses. These range from infectious diseases, such as bacterial and viral infections; innate conditions, such as mental illness or autoimmune disorders, or those caused by lifestyle, such as coronary heart disease. Despite the successes, problems still remain. Many bacteria and viruses are rapidly evolving resistance to drug strategies. Also, those in the developing world, who are most at risk from infection, often benefit least from drugs, due to prohibitive costs and reduced investment in treatment.