OPEN MINDS, The Behavioral Health & Social Service Industry Analyst Industry Statistics In 2005, an estimated 19.7 million Americans over the age of 12, approximately 8.1% of this poulation, admitted to being current users of illicit drugs, meaning they had used an illicit drug during the month prior to be interviewed for the study. Of all the types of illicit drugs, marijuana tops the list with 14.6 million users (6% of the population), followed by misuse of psychotherapeutics with 6.4 million users (2.6%). Of . . .