MARIJUANA contains many substances, collectively identified as "cannabinoids."   Of these, the most important one is delta-9-tetrahydrocannabinol (THC).  This is the major psychoactive compound, and the compound which is of most forensic and pharmacologic interest.  THC is metabolized first to Hydroxy-THC (THC-OH),  which is active, then to the inactive 11-nor-delta-9-THC Carboxylic acid (THC-A or THC-COOH).

Marijuana use has traditionally been monitored by the detection of THC-A.  However, the presence of THC-A in the urine only indicates marijuana use, not intoxication.  Because THC is stored in body fat, long term use of marijuana results in the storage of THC in the body.  As THC leaches out of the body fat, it is metabolized by the liver into THC-OH, then into THC-A.  Long term use of marijuana can result in the finding of THC-A for several months after the last use of marijuana (1).

Many attempts have been made to determine the time of last use of marijuana by the measurement of THC, THC-OH, and THC-A in urine samples (2).  However, these have been limited by the analytical technology used (GC/MS).  In particular, measurements of THC and THC-OH require much greater sensitivity than do those for THC-A, because THC-A is commonly present in much greater concentrations.  The most common way to measure cannabinoids is with gas chromatography - mass spectrometry (GC/MS).  However, GC/MS, as it is most commonly implemented, does not provide sufficiently accurate or precise data for the calculations which are attempted in the referenced publications.  Pharmacokinetic calculations are dependent upon the accuracy and precision of the measurements (3).

We have found that the three important cannabinoids can be measured with excellent precision, accuracy, and specificity by the use (4) of Tandem High Pressure Liquid Chromatography - Mass Spectrometry (HPLC/MS/MS). The limits of quantitation for all three substances are 400pg/mL. We also are able to measure THC and THC-A in hair and other non-traditional matrices.

Because THC and THC-OH are essentially absent from the urine 4-6 hours after the last use of marijuana, a finding that those two compounds are absent from a urine sample will show that there was no recent effective use of marijuana. 

Attempts to correlate THC concentration with effects have been made for many years, but are fraught with problems (5).

Unfortunately, many laboratories fail to follow the SOFT Guidelines (Society of Forensic Toxicologists) in an attempt to measure extremely low concentrations of cannabinoids of interest (1-10ng/mL.)  We follow the SOFT Guidelines.  RML is CLIA certified and licensed by the Colorado Department of Public Health and Environment to perform analyses of blood and urine for the presence and quantitation of drugs.

We also offer the analysis of various cannabinoid substances, such as JWH-018.  A recent review (6) has been published that brings together much of the information available regarding "cannabis alternatives." 


For additional information on cannabinoids or other substances of forensic interest, contact either Dr. Patricia Sulik or Dr. Robert Lantz.

1.    Ellis, GM, et al, Clinical Pharmacology Therapeutics,  38, 572-578 (1985).

2.    Heustis, MA and Cone, EJ,  J. Analytical Toxicology,  22, 445-454 (1998).

3.    Berg, MJ, and Lantz, RK,  Therapeutic Drug Monitoring 5, 379-387 (1983).

4.    Lantz, RK and Sulik, PL, "LCMS-The Real World" invited presentation at the SOFT Annual Meeting, Raleigh, NC, OCTOBER 2007.

5.    Grotenhermen, F, et al, "Developing limits for driving under cannabis," Addiction 102, 1910-1917

6.    Rosenbaum, C. et al, "...A Review of Herbal Marijuana Alternatives..." J. Medical Toxicology 8, 15-32 (2012). 

FT. COLLINS, CO   80525

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LAST UPDATED:     16 APRIL 2012