Marijuana Drug Information

Classification

Metabolism

When marijuana is smoked, THC is rapidly absorbed through the lungs and enters the bloodstream in minutes. Following oral ingestion, THC does not reach the bloodstream for approximately 1-1.5 hours. Once in the blood, THC is bound to blood proteins and carried throughout the body where it is either absorbed into body tissues (including the brain, heart, and fat) or transformed by the liver into11-hydroxy-THC and carboxy-THC. These primary metabolites are subsequently conjugated to glucuronic acid to make them water soluble. These water soluble metabolites, are readily excreted into the urine, with the inactive metabolite carboxy-THC-glucuronide being the predominant metabolite detected. Initially, THC is quickly absorbed into the body tissues and then is slowly released back into the blood stream where it is carried to the liver and metabolized. Because THC tends to be stored in fatty tissues, it accumulates faster than it can be eliminated in chronic repetitive smokers. This accumulation leads to extended retention of THC which is then eliminated from the body at a relatively constant rate with an average elimination half-life being estimated at 18-30 hours. Urinary concentrations of THC are very difficult to interpret due to variables such as dosage of THC ingested, frequency of use, timing of urine collection relative to last exposure to marijuana, rate of release of stored cannabinoids in adipose tissue, and an individual's hydration state. Therefore, the detection of THC metabolites in the urine is only an indication of past marijuana use and is not related to the degree of intoxication or impairment.

Abuse

The psychological effects of THC include euphoria, relaxation, slowed psycho-motor response, an altered sense of time, short term memory impairment and impairment of multi- tasking performance.

THC Retention Time

• Infrequent (less than twice/week) Smoking: When screening assays of 50 ng/mL or greater are used, urine samples will generally be positive for 1-3 days.
• Regular (several times per week) Smoking: May result in urine specimens testing positive for 7-21 days.
• Chronic (daily) Smoking: An individual who smokes marijuana daily for prolonged periods of time can test positive for 30 days or longer.
• Oral Ingestion: Metabolic profiles in urine samples cannot generally differentiate between marijuana ingested orally versus marijuana ingested by smoking. As with smoking, the detection window will lengthen with amount of THC absorbed into the bloodstream and frequency of use. Since absorption of THC in the small intestine is poor, the amount of THC absorbed will be 4-7 times lower when the same dose is administered orally versus smoking.
• Passive Inhalation: In general, routine passive exposure to marijuana smoke will not result in a positive result for cannabinoids in excess of a 50 ng/mL screening cut-off.

Laboratory drug testing: Methods of Analysis

The most common screening methods used to detect cannabinoids in urine include enzyme immunoassay (EIA). Urine cannabinoid immunoassays are usually optimized for the detection of carboxy-THC, but also react with other cannabinoids present in the urine. Because of this cross-reactivity and differing performance characteristics of each test, the values from EIA cannot be reliably compared with confirmatory techniques such as GC-MS and LC-MS-MS. While immunoassay cross-reactivity to non-cannabinoid compounds is rare, positive EIA results should be confirmed by alternate specific analytical methods. The chromatographic methods; GC-MS and LC-MS/MS meet this requirement and provide the most reliable test results.