Saliva is a refined version of plasma, that has the capability to contain trace amounts of drugs and their ensuing metabolites for a period of 24-36 hours. This forms the basis of saliva drug test. It is also known as oral fluid drug test.
Here are the detection time for some drug test items:
Alcohol - from time of intake to 12 hours.
PCP - from a few minutes after ingestion to the next three days.
Methamphetamine and ecstasy - half an hour from ingestion up to 3 days.
Amphetamines - a few minutes to 3 days of consumption.
Barbiturates - less than an hour after ingestion up to 3 days.
Opiates - from an hour after intake to 3 days.
Cocaine - a few minutes after ingestion up to one day.
Cannabis - a few minutes after ingestion up to one day.