Researchers who compared self-reports of tobacco and other drug use with urine and hair samples found that most users accurately reported their own consumption.

The Substance Abuse and Mental Health Services Administration (SAMHSA) report, "Comparing Drug Testing and Self Report of Drug Use Among Youths and Young Adults in the General Population," found that self-reports and urine tests for past-30-days smoking were in agreement 84.6 percent of the time. For marijuana, the agreement rate was 89.8 percent.

Urine tests and self-reports of cocaine use in the past seven days were in agreement 98.5 percent of the time.

"This validity study concluded that biological drug tests can be used as objective markers of drug use to verify self reports among youth and young adults," the researchers noted.