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Cannabis (pot - weed)
Detection of Cannabinoids in Urine
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.
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