Medicalization (or medicalisation) is the process by which human conditions and problems come to be defined and treated as medical conditions, and thus become the subject of medical study, diagnosis, prevention, or treatment. Medicalization can be driven by new evidence or hypotheses about conditions; by changing social attitudes or economic considerations; or by the development of new medications or treatments. Medicalization is studied from a sociologic perspective in terms of the role and power of professionals, patients, and corporations, and also for its implications for ordinary people whose self-identity and life decisions may depend on the prevailing concepts of health and illness. Once a condition is classified as medical, a medical model of disability tends to be used in place of a social model. Medicalization may also be termed "pathologization" or (pejoratively) "disease mongering". The concept of medicalization was devised by sociologists to explain how medical knowledge is applied to behaviors which are not self-evidently medical or biological. The term medicalization entered the sociology literature in the 1970s in the works of Irving Zola, Peter Conrad and Thomas Szasz, among others. These sociologists viewed medicalization as a form of social control in which medical authority expanded into domains of everyday existence, and they rejected medicalization in the name of liberation. This critique was embodied in works such as Conrads "The discovery of hyperkinesis: notes on medicalization of deviance", published in 1973 (hyperkinesis was the term then used to describe what we might now call ADHD). Nevertheless, opium was used to pacify children in ancient Egypt before 2000 BC.