"Illegal drugs are widely used among the arrestee population. Two thirds of all arrestees tested positive for at least one substance in their system at the time of arrest and 15 percent or more in all sites test positive for more than one substance. The most common substances in all but three sites are marijuana, cocaine, opiates and methamphetamine."
Source
Office of National Drug Control Policy. ADAM II Annual Report (Arrestee Drug Abuse Monitoring Program). Washington DC: Office of the President. p. 37.
http://www.ibhinc.org/pdfs/AD…
