Drug Detection Times

The detection of drugs and/or their metabolites in urine is influenced by the pharmacokinetic processes of absorption, distribution, metabolism and excretion. The relative importance of these processes varies from drug to drug, and determines whether the parent drug or metabolites will be detected. Dose size and route of administration are among the factors which determine the period after use during which the drugs or metabolites might be detected.

Examples of the variables that have to be considered are:

the rapid metabolism of cocaine, resulting in use almost exclusively identified by the metabolite benzoylecgonine
the deposition of THC (cannabis) into fatty tissues, released slowly over time.
the metabolism of heroin and codeine to morphine

The combined effects of distribution and metabolism means that most drugs clear rapidly from the bloodstream. Excretion of drugs in urine may continue at a detectable level for some time. The level is variable through the day, and from day to day - urine drug levels may not correlate with blood concentrations. Urine drug tests can provide evidence of recent use, but do not indicate dose size, pattern of use, or impairment.

Duration of positive results in urine after a typical dose taken by a drug abuser
SUBSTANCE	DETECTABLE FOR:
Amphetamine	1-2 days
Barbiturates	1-5 days (longer for Phenobarbitone)
Benzodiazepines	varies according to drug
Cannabis	2 - 21 days
Cocaine	2-3 days
Codeine	1-2 days
Dihydrocodeine	1-2 days
LSD	2-3 days
Methadone	1-2 days
Morphine	1-2 days
Propoxyphene	2-4 days
Alcohol	depends on amount consumed
These detection times are a guide only and will be affected by variables such as size of dose, frequency of use and individual metabolism

Knowledge of pharmacokinetics is exploited by people trying to defeat the drug testing process.