Laboratory Studies

Urine testing

Cannabinoids can be detected in the urine for as many as 21 days after use in persons chronically using marijuana, because these lipid-soluble metabolites are slowly released from fat cells into the blood; however, 1-5 days is the normal urine-positive period.

The primary method for urinalysis detection is enzyme immunoassay or radioimmunoassay. This method is inexpensive, quick, and accurate. This is also useful for confirmation of abstinence.

Urine samples are difficult to obtain from people who are addicted, and providing a urine sample is easily evaded. Urine toxicology testing should be performed under supervised conditions to ensure reliability of results.

Gas chromatography in combination with mass spectrometry and/or thin-layer chromatography is used to confirm positive results, especially in legal proceedings.

With all types of tests mentioned, including thin-layer chromatography, false-negative results tend to be more common than false-positive results.

Blood testing

Blood samples may be used to measure quantitative levels of cannabinoids.^[31]Serial monitoring of tetrahydrocannabinol (THC)–COOH to creatinine ratios can distinguish between recent use and residual excretion. To assess the extent of cannabis use, determination of free and bound THC-COOH can be useful.

Blood analysis is the preferred method of detection for interpretation of acute effects. The cannabis influence factor is a tool used to interpret concentrations of THC and its metabolites in forensic cases. Absolute driving inability has been proposed in the case of cannabis influence factor of 10 or higher. The higher the cannabis influence factor, the more recent the cannabis abuse.

Blood samples must be taken within a prescribed 8-day period, and THC-COOH concentration greater than 75 ng/mL is associated with regular consumption of cannabis. THC-COOH concentration less than 5 ng/mL is associated with occasional consumption.

Hair analysis

Hair analysis is not a sensitive enough tool to detect cannabinoids.^[31]THC, and the main metabolite THC-COOH, do not incorporate to a great extent into hair. TCH-COOH is not highly bound to melanin. Hence, concentrations in hair are much lower when compared with other drugs of abuse. Because TCH is present in cannabis smoke, it can also be incorporated into hair simply by second-hand exposure.

Saliva testing

Saliva testing is a newer technology for detection. The presence of delta-9-THC in oral fluid is a better indication of recent use than the presence of 11-nor-delta-9-THC-9-COOH detected in urine. Therefore, the probability that a user is experiencing effects is higher. This may prove especially useful in the monitoring of driving while under the influence.

Imaging Studies

Although no confirmatory imaging study exists for marijuana use, pilot investigations involving neuroimaging of marijuana smokers performing various mental tasks have revealed many differences in comparative levels of activity in many regions of the brain with respect to controls.

Functional MRI and diffusion tensor imaging techniques demonstrate significant differences in the magnitude and pattern of signal intensity change within the anterior cingulate and the dorsolateral prefrontal cortex while performing standardized tasks in chronic marijuana smokers compared with healthy controls.

Neuroimaging studies, such as CT scanning, MRI, and positron emission tomography scanning, are extensively used to study the neurobiological effects of cannabis abuse but are not clinically useful in the definitive determination of recent abuse.

Treatment & Management

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Media Gallery

Cannabis sativa.
The major psychoactive component of marijuana is tetrahydrocannabinol (THC).

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Author

Lawrence Genen, MD, MBA Board Certified Psychiatrist; Diplomate, American Board of Psychiatry and Neurology; Founder, The Genen Group - A Multi-Specialty Psychiatry and Psychotherapy Practice

Disclosure: Nothing to disclose.

Coauthor(s)

John Franzen, MD Resident Physician, Department of Psychiatry, University of Nebraska-Creighton University

Disclosure: Nothing to disclose.

William F Haning, III, MD, FASAM, DFAPA Professor of Psychiatry, Director of Graduate Affairs, Office of the Dean, Program Director, Addiction Psychiatry/Medicine, Department of Psychiatry, University of Hawaii, John A Burns School of Medicine; Principal Investigator and Co-Director, Pacific Addiction Research Center

William F Haning, III, MD, FASAM, DFAPA is a member of the following medical societies: Alpha Omega Alpha, American Academy of Addiction Psychiatry, American Medical Association, American Psychiatric Association, American Society of Addiction Medicine, Association of Military Surgeons of the US, Hawaii Medical Association

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Chief Editor

David Bienenfeld, MD Professor, Departments of Psychiatry and Geriatric Medicine, Wright State University, Boonshoft School of Medicine

David Bienenfeld, MD is a member of the following medical societies: American Medical Association, American Psychiatric Association, Association for Academic Psychiatry

Disclosure: Nothing to disclose.

Additional Contributors

Barry I Liskow, MD Professor of Psychiatry, Vice Chairman, Psychiatry Department, Director, Psychiatric Outpatient Clinic, The University of Kansas Medical Center

Disclosure: Nothing to disclose.

Acknowledgements

The authors and editors of Medscape Reference gratefully acknowledge the contributions of previous authors Robert C Daly, MB, ChB, MPH, BCh; Can M Savasman, MD; Caroline Fisher, MD, PhD; and Lina Cassandra Vawter, MD to the development and writing of this article.