Marijuana is the most widely used illicit drug in the United States. Delta-9-tetrahydrocannabinol (THC) is the primary psychoactive substance, although the marijuana plant contains many related cannabinoid compounds. Marijuana is generally known by the botanical name Cannabis Sativa and consists of the flowering tops and leaves of the plant. It is distinguished from Cannabis Americana (hemp) by the psychoactive effects of delta-9-THC depending on cultivation techniques, gender of the plant and other factors. The potency of confiscated marijuana has been increasing in recent years and its use spreading throughout the population. As the use of marijuana has increased, concerns over the health of the users and effects on society have grown. Recent methods of urinary detection have indicated that between 10% and 20% of the population test positive. Of particular concern is the use of marijuana by persons in the military, in classified or security positions, and those operating machinery or driving automobiles.

Pharmacological Effects
Smoked doses of 20 mg (two potent cigarettes) of delta-9-THC will produce increases of 20 to 50 beats per minute in heart rate, impairment of short term memory and concentration, possibly mood changes such as euphoria, altered perception of time, hunger, and other effects. At higher doses, marijuana interferes with motor coordination and complex task functioning. Activities requiring a high degree of alertness such as operating machinery, driving or working in dangerous environments are contraindicated. Pharmacological effects from inhaled drugs begins almost immediately. Delta-9-THC plasma levels peak 10 to 20 minutes post inhalation and begin to decline. Effects last for two to three hours.

Studies indicate that marijuana and alcohol potentate one another more than either drug alone. Thus, smaller amounts of ethanol and marijuana may increase toxic effects. Peak levels of marijuana metabolites in the urine occur about five hours post dose and thus are not useful in predicting the degree of intoxication. Urinary presence only indicates recent exposure. Note marijuana metabolite testing is available only in urine, not hair.

Laboratory Methods
Immunoassays are used to initially screen specimens for cannabinoids (THC). Confirmation of positives is by GC/MS.

Cutoff and Detection Post Dose
The initial screening cutoff level is 50 ng/ml. The GC/MS cutoff level is 15 ng/ml. The elimination half-life of marijuana ranges from 14-38 hours. At the initial cutoff of 50 ng/ml, the daily user will remain positive for perhaps 7 to 30 days after cessation. At the confirmation level of 15 ng/ml, the frequent user will be positive for perhaps as long as 15 weeks. Marijuana metabolites' storage and slow release from lipid tissues is the reason for this long detection period.

Passive Inhalation
Urine levels of 5 ng/ml have been reported from passive inhalation. One recent survey indicated that one subject in a passive inhalation experiment achieved a level of 23 ng/ml. This is unusual, but points out the usefulness of higher cutoff levels such as 50 ng/ml. The higher 50 ng/ml level eliminates the possibility of passive inhalation, is a level of very high reliability, and indicates more recent use.