The manner in which prescription drugs are marketed today can be readily understood if you read the 1928 book "Propaganda," by Edward Bernays, the father of PR.
Bernays knew that public relations business was less about selling things than about creating the conditions for things to sell themselves.
Pharmaceutical marketers, following in his footsteps, sell drugs by selling diseases -- a system known as "disease branding." Illnesses such as panic disorder, restless legs syndrome, bipolar disorder, and ADHD were once considered rare until a marketing campaign transformed the brand in order to sell more drugs.
According to CNN:
"If all drugs were harmless, disease branding would be relatively harmless, too. But no drug is completely benign ... Detrol can make elderly people delirious and may cause memory problems. Paxil is associated with sexual dysfunction and dependence ... Side effects like these are a part of every drug. But they are never part of the brand."