Cannabis drug testing

Last updated September 08, 2024

Cannabis drug testing describes various drug test methodologies for the use of cannabis in medicine, sport, and law. Cannabis use is highly detectable and can be detected by urinalysis, hair analysis, as well as saliva tests for days or weeks.

Unlike alcohol, for which impairment can be reasonably measured using a breathalyser (and confirmed with a blood alcohol content measurement), valid detection for cannabis is time-consuming, and tests cannot determine an approximate degree of impairment. The lack of suitable tests and agreed-upon intoxication levels is an issue in the legality of cannabis, especially regarding intoxicated driving.

The concentrations obtained from such analyses can often be helpful in distinguishing active use from passive exposure, elapsed time since use, and extent or duration of use.

The Duquenois-Levine test is commonly used as a screening test in the field, but it cannot definitively confirm the presence of cannabis, as a large range of substances have been shown to give false positives.

Biological timeline

Most cannabinoids are lipophilic (fat soluble) compounds that easily store in fat, thus yielding a long elimination half-life relative to other recreational drugs.^[1] Metabolites of cannabis are usually detectable in urine drug tests from 3 days up to 10 days according to Redwood Laboratories; heavy users can produce positive tests for 30 days or longer after ceasing cannabis use.^[2]^[3] The length of time may vary to some degree according to metabolism, quantity, and frequency of use.^[4]

Testing methods

Urine testing

Marijuana use can be detected up to 3–5 days after exposure for infrequent users, 1–15 days for heavy users, and 1–30 days for chronic users and/or users with high body fat.^[5]^[6]

Under the typical 50 ng/mL cutoff used for cannabis testing in the United States, an occasional or on-off user would be very unlikely to test positive beyond 3–4 days since the last use, and a chronic user would be likely to test positive much beyond 7 days all the way up to 90 days in a urine or hair sample. Cited Health line article medically reviewed by Eloise Theisen RN, MSN, AGPCNOP-BC dated April 23 2024. Using a more sensitive cutoff of 20 ng/mL (less common but still used by some labs), the most likely maximum times are 7 days and 21 days, respectively. In extraordinary circumstances of extended marijuana use, detection times of more than 30 days are possible in some individuals at the 20 ng/mL cutoff.^[7]

However, every individual is different, and detection times can vary due to metabolism or other factors. It also depends on whether tetrahydrocannabinol (THC) or its metabolites are being tested for, the latter having a much longer detection time than the former. THC, the main psychoactive component of cannabis, may only be detectable in saliva and oral fluid for 2–24 hours in most cases.^[8]^[9]

The main metabolite excreted in the urine is 11-Nor-9-carboxy-THC, also known as THC-COOH. Most cannabis drug tests yield a positive result when the concentration of THC-COOH in urine exceeds 50 ng/mL.^[10] Urine testing is an immunoassay based test on the principle of competitive binding. Drugs which may be present in the urine specimen compete against their respective drug conjugate for binding sites on their specific antibody. During testing, a urine specimen migrates upward by capillary action. A drug, if present in the urine specimen below its cut-off concentration, will not saturate the binding sites of its specific antibody. The antibody will then react with the drug-protein conjugate and a visible colored line will show up in the test line region of the specific drug strip.^{[ citation needed ]}

Cannabis use is included in the "10-panel urine screen", as well as the "SAMHSA-5", the five drugs tested for in standard NIDA approved drug tests.

False positives have been known to be triggered by consuming hemp-seed bars, low THC cannabis and CBD supplements, although the more detailed, more expensive gas chromatography-mass spectrometer (GCMS) test can tell the difference.^[11]

In 2011, researchers at John Jay College of Criminal Justice reported that dietary zinc supplements can mask the presence of THC and other drugs in urine. Similar claims have been made in web forums on that topic.^[12] However, a 2013 study conducted by researchers at the University of Utah School of Medicine refute the possibility of self-administered zinc producing false-negative urine drug tests.^[13]

Common known pharmaceutical drugs which cause false positives in instant THC dip tests include:

Proton pump inhibitors ^[14]

Duquenois–Levine reagent

The Duquenois–Levine test is a simple chemical color reaction test initially developed in the 1930s by Pierre Duquénois.

To administer the test, a user simply has to mix the chemicals with a particle of the suspected substance; if the chemicals turn purple, this indicates the possibility of marijuana. But the color variations can be subtle, and readings can vary by examiner.

It was adopted in the 1950s by the United Nations as the preferred test for cannabis. Such tests are often distributed in snap-to-open glass vials.

Step 1 – addition of Duquenois reagent to dried petroleum ether extract
Step 2 – addition of hydrochloric acid
Step 3 – addition of chloroform

Azo dyes (Fast Blue B/BB)

The United Nations Office on Drugs and Crime (UNODC) found the azo dyes Fast Blue B (3,3'-dimethoxybiphenyl-4,4'-bisdiazonium chloride^[15]) and Fast Blue BB (4-benzoylamino-2,5-diethoxybenzenediazonium chloride^[16]) superior to Duquenois–Levine, and are currently the most recommended reagents used for cannabinoid testing. The dyes, as water-soluble salts, are typically applied during thin layer chromatography. They are extremely sensitive to a variety of cannabinoids, and very specific in reaction. Fast Blue BB is slightly slower than Fast Blue B, but the resulting colors are more vivid and intense. Due to concerns about Fast Blue B being carcinogenic Fast Blue BB is often used instead,^[17] although it too is a suspected carcinogen.^[18]^[19] Other Azo dyes which are suitable for cannabinoid detection, albeit inferior to Fast Blue B/BB, include Corinth V, Blue LGC, Garnet GC (GR), Red AV, Garnet GBO, Bordeaux GP, and Red P.^[19]

Beam's CBD Test

In 1911, Dr. W. Beam discovered that the tissue of hemp, which is typically low in THC but high in CBD, gives a purple color when treated with bases.^[20] The test is relatively simple and inexpensive, and typically involves placing the test sample in a solution of 5% potassium hydroxide and 95% ethanol.^[21] After approximately ten minutes, samples with CBD exhibit a violet/purple/pink color. The test is specific to CBD and does not react to THC.

Hair testing

Cannabis use is detectable with hair tests and is generally included in the standard hair test. Hair tests generally take the most recent 1.5 inches of growth and use those for testing. That provides a detection period of approximately 90 days.^[5] If an individual's hair is shorter than 1.5 inches, this detection period will be shorter. The detection window for body hair cannabis testing will be longer, because body hair grows slower than head hair and distorts the detection timeframe. Hair drug testing measures the marijuana parent metabolite embedded inside the hairshaft and eliminates external contamination as a source of a positive result. The detection window of hair drug testing for cannabis can be as low as 1 pg/mg.^[22]

Saliva testing

Cannabis is detectable by saliva testing. Just like blood testing, saliva testing detects the presence of parent drugs and not their inactive metabolites. This results in a shorter window of detection for cannabis by saliva testing.^[23] Delta 9 THC is the parent compound. If a saliva sample is tested in a lab, the detection level can be as low as 0.5 ng/mL (up to 72 hours after intake).^[24] Per National Institute on Drug Abuse saliva drug testing provides a reasonable alternative to other drug testing methods.^[25]

Blood testing

Cannabis is detectable in the blood for approximately 12–24 hours, with heavy/frequent use detectable in the blood for up to 7 days (depending on a person's blood renewal system).^{[ citation needed ]} Because they are invasive and difficult to administer, blood tests are used less frequently.^{[ citation needed ]} They are typically used in investigations of accidents, injuries and DUIs.^{[ citation needed ]}

Urine contains predominantly THC-COOH, while hair, oral fluid, and sweat contain primarily THC. Blood may contain both substances, with the relative amounts dependent on the recency and extent of usage.^[26]^[27]^[28]

Neurological testing

Although unlikely to be used in court, electroencephalography (EEG) results show somewhat more persistent alpha waves of slightly lower frequency than the norm.^[29] Cannabinoids produce a "marked depression of motor activity" via activation of neuronal cannabinoid receptors belonging to the CB1 subtype.^[30]

Related Research Articles

<span class="mw-page-title-main">Tetrahydrocannabinol</span> Psychoactive component of cannabis

Tetrahydrocannabinol (THC) is a cannabinoid found in cannabis. It is the principal psychoactive constituent of cannabis and one of at least 113 total cannabinoids identified on the plant. Although the chemical formula for THC (C₂₁H₃₀O₂) describes multiple isomers, the term THC usually refers to the delta-9-THC isomer with chemical name (−)-trans-Δ⁹-tetrahydrocannabinol. It is a colorless oil.

<span class="mw-page-title-main">Effects of cannabis</span>

The short-termeffects of cannabis are caused by many chemical compounds in the cannabis plant, including 113 different cannabinoids, such as tetrahydrocannabinol (THC), and 120 terpenes, which allow its drug to have various psychological and physiological effects on the human body. Different plants of the genus Cannabis contain different and often unpredictable concentrations of THC and other cannabinoids and hundreds of other molecules that have a pharmacological effect, so the final net effect cannot reliably be foreseen. Acute effects while under the influence can sometimes include euphoria or anxiety. Although some assert that cannabidiol (CBD), another cannabinoid found in cannabis in varying amounts, may alleviate the adverse effects of THC that some users experience, little is known about CBD's effects on humans. Cannabinoid receptor antagonists have previously been tested as antidotes for cannabis intoxication with success, reducing or eliminating the physiological and psychological effects of intoxication. Some of these products are currently in development as cannabis antidotes.

Medical cannabis, medicinal cannabis or medical marijuana (MMJ), refers to cannabis products and cannabinoid molecules that are prescribed by physicians for their patients. The use of cannabis as medicine has a long history, but has not been as rigorously tested as other medicinal plants due to legal and governmental restrictions, resulting in limited clinical research to define the safety and efficacy of using cannabis to treat diseases.

Cannabinoids are several structural classes of compounds found in the cannabis plant primarily and most animal organisms or as synthetic compounds. The most notable cannabinoid is the phytocannabinoid tetrahydrocannabinol (THC) (delta-9-THC), the primary psychoactive compound in cannabis. Cannabidiol (CBD) is also a major constituent of temperate cannabis plants and a minor constituent in tropical varieties. At least 113 distinct phytocannabinoids have been isolated from cannabis, although only four have been demonstrated to have a biogenetic origin. It was reported in 2020 that phytocannabinoids can be found in other plants such as rhododendron, licorice and liverwort, and earlier in Echinacea.

A drug test is a technical analysis of a biological specimen, for example urine, hair, blood, breath, sweat, or oral fluid/saliva—to determine the presence or absence of specified parent drugs or their metabolites. Major applications of drug testing include detection of the presence of performance enhancing steroids in sport, employers and parole/probation officers screening for drugs prohibited by law and police officers testing for the presence and concentration of alcohol (ethanol) in the blood commonly referred to as BAC. BAC tests are typically administered via a breathalyzer while urinalysis is used for the vast majority of drug testing in sports and the workplace. Numerous other methods with varying degrees of accuracy, sensitivity, and detection periods exist.

Forensic toxicology is a multidisciplinary field that combines the principles of toxicology with expertise in disciplines such as analytical chemistry, pharmacology and clinical chemistry to aid medical or legal investigation of death, poisoning, and drug use. The paramount focus for forensic toxicology is not the legal implications of the toxicological investigation or the methodologies employed, but rather the acquisition and accurate interpretation of results. Toxicological analyses can encompass a wide array of samples. In the course of an investigation, a forensic toxicologist must consider the context of an investigation, in particular any physical symptoms recorded, and any evidence collected at a crime scene that may narrow the search, such as pill bottles, powders, trace residue, and any available chemicals. Armed with this contextual information and samples to examine, the forensic toxicologist is tasked with identifying the specific toxic substances present, quantifying their concentrations, and assessing their likely impact on the individual involved.

<span class="mw-page-title-main">Cannabidiol</span> Phytocannabinoid discovered in 1940

Cannabidiol (CBD) is a phytocannabinoid, one of 113 identified cannabinoids in cannabis plants, along with tetrahydrocannabinol (THC), and accounts for up to 40% of the plant's extract. It was discovered in 1940 and as of 2022, clinical research on CBD included studies related to the treatment of anxiety, addiction, psychosis, movement disorders, and pain, but there is insufficient high-quality evidence that CBD is effective for these conditions. CBD is sold as a herbal dietary supplement and promoted with yet unproven claims of particular therapeutic effects.

Cannabis, also known as marijuana or weed, among other names, is a non-chemically uniform drug from the cannabis plant. Native to Central or South Asia, the cannabis plant has been used as a drug for both recreational and entheogenic purposes and in various traditional medicines for centuries. Tetrahydrocannabinol (THC) is the main psychoactive component of cannabis, which is one of the 483 known compounds in the plant, including at least 65 other cannabinoids, such as cannabidiol (CBD). Cannabis can be used by smoking, vaporizing, within food, or as an extract.

<span class="mw-page-title-main">THC-O-acetate</span> Acetate ester of tetrahydrocannabinol (THC)

THC-O-acetate is the acetate ester of THC. The term THC-O-acetate and its variations are commonly used for two types of the substance, dependent on which cannabinoid it is synthesized from. The difference between Δ⁸-THC and Δ⁹-THC is bond placement on the cyclohexene ring.

<span class="mw-page-title-main">11-Hydroxy-THC</span> Active metabolite of Δ9-THC

11-Hydroxy-Δ⁹-tetrahydrocannabinol, usually referred to as 11-hydroxy-THC is the main active metabolite of tetrahydrocannabinol (THC), which is formed in the body after Δ⁹-THC is consumed.

<span class="mw-page-title-main">JWH-018</span> Chemical compound

JWH-018 (1-pentyl-3-(1-naphthoyl)indole, NA-PIMO or AM-678) is an analgesic chemical from the naphthoylindole family that acts as a full agonist at both the CB₁ and CB₂ cannabinoid receptors, with some selectivity for CB₂. It produces effects in animals similar to those of tetrahydrocannabinol (THC), a cannabinoid naturally present in cannabis, leading to its use in synthetic cannabis products that in some countries are sold legally as "incense blends".

<span class="mw-page-title-main">11-Nor-9-carboxy-THC</span> Main secondary metabolite of THC

11-Nor-9-carboxy-Δ⁹-tetrahydrocannabinol, often referred to as 11-nor-9-carboxy-THC or THC-11-oic acid, is the main secondary metabolite of tetrahydrocannabinol (THC) which is formed in the body after cannabis is consumed.

<span class="mw-page-title-main">Synthetic cannabinoids</span> Designer drugs

Synthetic cannabinoids are a class of designer drug molecules that bind to the same receptors to which cannabinoids in cannabis plants attach. These novel psychoactive substances should not be confused with synthetic phytocannabinoids or synthetic endocannabinoids from which they are in many aspects distinct.

Dronabinol, sold under the brand names Marinol and Syndros, is the generic name for the molecule of delta-9-tetrahydrocannabinol (THC) in the pharmaceutical context. It has indications as an appetite stimulant, antiemetic, and sleep apnea reliever and is approved by the U.S. FDA as safe and effective for HIV/AIDS-induced anorexia and chemotherapy-induced nausea and vomiting.

Cannabinoid hyperemesis syndrome (CHS) is recurrent nausea, vomiting, and cramping abdominal pain that can occur due to prolonged, high-dose cannabis use. These symptoms may be relieved temporarily by taking a hot shower or bath. Complications are related to persistent vomiting and dehydration which may lead to kidney failure and electrolyte problems.

<span class="mw-page-title-main">Tetrahydrocannabinolic acid</span> THC precursor

Tetrahydrocannabinolic acid is a precursor of tetrahydrocannabinol (THC), an active component of cannabis.

Two main questions arise in the law surrounding driving after having ingested cannabis: (1) whether cannabis actually impairs driving ability, and (2) whether the common practice of testing for THC is a reliable means to measure impairment. On the first question, studies are mixed. Several recent, extensive studies–including one conducted by the National Highway Traffic Safety Administration and one conducted by the American Automobile Association (AAA)–show that drivers with detectable THC in their blood are no more likely to cause car crashes than drivers with no amount of THC in their blood. Others show that cannabis can impair certain abilities important to safe driving –but no studies have been able to show that this increases the actual risk of crashing, or that drivers with THC in their blood cause a disproportionate number of crashes. On the second question, the studies that have been conducted so far have consistently found that THC blood levels and degree of impairment are not closely related. No known relationship between blood levels of THC and increased relative crash risk, or THC blood levels and level of driving impairment, has been shown by single-crash or classic-control studies. Thus, even though it is possible that cannabis impairs driving ability to some extent, there are currently no reliable means to test or measure whether a driver was actually impaired.

Occupational health concerns over the use of cannabis among workers are becoming increasingly important as cannabis becomes legal in more areas of the US. Of note, employers have concerns of workers either coming to work acutely impaired or recent use of cannabis still being detected in the body. Employment issues such as ADA law as it relates to accommodations for cannabis, paying unemployment benefits or paying out workers compensation benefits and disability claims are all important issues. While federal law still prohibits use, employers in different states have taken different stances based on whether they are federal contractors, perform safety sensitive work or whether the cannabis use is acutely impairing the employee.

Δ-8-tetrahydrocannabinol is a psychoactive cannabinoid found in the Cannabis plant. It is an isomer of delta-9-tetrahydrocannabinol, the compound commonly known as THC, with which it co-occurs in hemp; natural quantities of ∆⁸-THC found in hemp are low. Psychoactive effects are similar to that of Δ⁹-THC, with central effects occurring by binding to cannabinoid receptors found in various regions of the brain.

<span class="mw-page-title-main">Cannabitriol</span> Group of isomers

Cannabitriol ((+)-CBT, (S,S)-9,10-Dihydroxy-Δ^6a(10a)-THC) is a phytocannabinoid first isolated in 1966, an oxidation product of tetrahydrocannabinol which has been identified both as a trace component of cannabis and as a metabolite in cannabis users. Its pharmacology has been little studied, though it has been found to act as an antiestrogen and aromatase inhibitor.

References

↑ Gunasekaran, N; Long, LE; Dawson, BL; Hansen, GH; Richardson, DP; Li, KM; Arnold, JC; McGregor, IS (November 2009). "Reintoxication: the release of fat-stored Δ9-tetrahydrocannabinol (THC) into blood is enhanced by food deprivation or ACTH exposure". British Journal of Pharmacology. 158 (5): 1330–1337. doi:10.1111/j.1476-5381.2009.00399.x. ISSN 0007-1188. PMC 2782342 . PMID 19681888.
↑ Choices, N. H. S. (2016-12-12). "How long does cannabis stay in the body after smoking? - Health questions - NHS Choices". Archived from the original on 2015-07-16. Retrieved 2017-01-09.
↑ "Marijuana | Drug Info | Resources | Redwood Toxicology Laboratory". www.redwoodtoxicology.com. Archived from the original on 2017-01-10. Retrieved 2017-01-09.
↑ "Weed Can Show Up in a Physical Urine Test | 24/7 Help". Los Angeles DUI Attorney.com. Retrieved 2024-03-03.
1 2 Erowid Cannabis (Marijuana) Vault: Drug Testing Archived 2016-09-02 at the Wayback Machine . Erowid.org (2010-02-28). Retrieved on August 7, 2011.
↑ Marijuana Detection Time Shorter Than Previously Assumed Archived 2016-09-02 at the Wayback Machine . norml.org (2006-02-23). Retrieved on March 13, 2012.
↑ Cary, Paul L. (April 2006). "The Marijuana Detection Window: Determining The Length Of Time Cannabinoids Will Remain Detectable In Urine Following Smoking A Critical Review Of Relevant Research And Cannabinoid Detection Guidance For Drug Courts" (PDF). National Drug Court Institute. Vol. IV, no. 2. Archived (PDF) from the original on 2016-04-22. Retrieved 2016-08-29.
↑ "How long does marijuana stay in your system? Blood, urine, and hair". www.medicalnewstoday.com. 2019-01-29. Retrieved 2024-03-03.
↑ "Current Knowledge on Cannabinoids in Oral Fluid".
↑ Goodwin, Robert S.; Darwin, William D.; Chiang, C. Nora; Shih, Ming; Li, Shou-Hua; Huestis, Marilyn A. (2008-10-01). "Urinary Elimination of 11-Nor-9-Carboxy-Δ9-tetrahydrocannnabinol in Cannabis Users During Continuously Monitored Abstinence". Journal of Analytical Toxicology. 32 (8): 562–569. doi:10.1093/jat/32.8.562. ISSN 0146-4760. PMC 2587336 . PMID 19007504.
↑ Hammond, Robert L. (2019-10-11). "Three Main Differences Between CBD and THC". Archived from the original on 2020-08-14. Retrieved 2020-07-03.
↑ Venkatratnam, Abhishek; Lents, Nathan H. (July 2011). "Zinc Reduces the Detection of Cocaine, Methamphetamine, and THC by ELISA Urine Testing". Journal of Analytical Toxicology. 35 (6): 333–340. doi: 10.1093/anatox/35.6.333 . PMID 21740689. Archived from the original on 2012-05-18. Retrieved 2016-08-29.
↑ Lin, Chia-Ni; Strathmann, Frederick (July 10, 2013). "Elevated Urine Zinc Concentration Reduces the Detection of Methamphetamine, Cocaine, THC and Opiates in Urine by EMIT" (PDF). Journal of Analytical Toxicology. 37 (9): 665–669. doi: 10.1093/jat/bkt056 . PMID 23843421. Archived (PDF) from the original on January 10, 2016. Retrieved August 29, 2016.
↑ "Protonix Drug Interaction Sheet" (PDF). Food and Drug Administration. Pfizer. Archived (PDF) from the original on 13 March 2018. Retrieved 11 December 2017.
↑ "Fast Blue B Salt V001655". Archived from the original on 2023-04-20. Retrieved 2017-06-08.
↑ "Fast Blue BB Salt hemi(zinc chloride) salt F3378". Archived from the original on 2016-02-02. Retrieved 2017-06-08.
↑ Cole, Michael D. (2003-05-07). The Analysis of Controlled Substances . John Wiley and Sons. p. 60. ISBN 9780471492528.
↑ "UNODC - Bulletin on Narcotics - 1969 Issue 4 - 005". Archived from the original on 2016-03-03. Retrieved 2017-06-08.
1 2 "UNODC - Bulletin on Narcotics - 1974 Issue 4 - 003". Archived from the original on 2018-04-06. Retrieved 2017-06-08.
↑ Preedy, Victor R. (2016-12-31). Handbook of Cannabis and Related Pathologies: Biology, Pharmacology, Diagnosis, and Treatment. Academic Press. ISBN 9780128008270. Archived from the original on 2023-04-20. Retrieved 2017-09-09.
↑ Starks, Michael (January 1990). "Marijuana Chemistry - Genetics, Processing & Potency" (PDF). Archived from the original (PDF) on 2017-08-04. Retrieved 2019-10-28.
↑ "Hair drug testing question and answers" (PDF). Quest Diagnostics. Archived from the original (PDF) on 2019-07-26. Retrieved 2012-10-24.
↑ "The ABCs of Marijuana and Drug Testing". NORML.org. Archived from the original on 2012-06-14. Retrieved 2012-10-23.
↑ "Journal of Analytical Toxicology, Vol 25, November/December 2002". Forensic Fluids Laboratory. Archived from the original on 2019-10-24. Retrieved 2015-09-15.
↑ "Testimony on Federal Workplace Drug-Testing by Edward J. Cone, PH.D. Before the House Committee on Commerce, Subcommittee on Oversight and Investigations". Department of Health & Human Services. July 23, 1998. Archived from the original on 2001-07-22.
↑ Coulter, C; Taruc, M; Tuyay, J; Moore, C (2009). "Quantitation of tetrahydrocannabinol in hair using immunoassay and liquid chromatography with tandem mass spectrometric detection". Drug Test. Anal. 1 (234–239): 234–239. doi:10.1002/dta.40. PMID 20355201.
↑ Schwope, DM; Milman, G; Huestis, MA (2010). "Validation of an enzyme immunoassay for detection and semiquantification of cannabinoids in oral fluid". Clin. Chem. 56 (6): 1007–1014. doi:10.1373/clinchem.2009.141754. PMC 3159868 . PMID 20360126.
↑ Huestis MA, Scheidweiler KB, Saito T, Fortner N, Abraham T, Gustafson RA, Smith ML (2008). "Excretion of Δ9-Tetrahydrocannabinol in Sweat". Forensic Sci. Int. 174 (2–3): 173–177. doi:10.1016/j.forsciint.2007.04.002. PMC 2277330 . PMID 17481836.
↑ H.K. Kalant; W.H.E. Roschlau (1998). Principles of Medical Pharmacology (6th ed.). pp. 373–375.
↑ Andersson, M.; Usiello, A; Borgkvist, A; Pozzi, L; Dominguez, C; Fienberg, AA; Svenningsson, P; Fredholm, BB; et al. (2005). "Cannabinoid Action Depends on Phosphorylation of Dopamine- and cAMP-Regulated Phosphoprotein of 32 kDa at the Protein Kinase A Site in Striatal Projection Neurons". Journal of Neuroscience. 25 (37): 8432–8. doi:10.1523/JNEUROSCI.1289-05.2005. PMC 6725667 . PMID 16162925.