Marijuana

Kevin M. Gray

Amanda P. Roper

Marijuana is the most commonly used illicit substance among adolescents and young adults (AYAs) in the US and the world. Its psychoactive and pharmacologic effects are well characterized, but variations in potency and composition, as well as many other individual and environmental variables, may influence these effects. Young people appear to be particularly prone to adverse effects of chronic marijuana use, most notably including cannabis use disorders and cognitive impairments. Additionally, adolescent marijuana use is associated with adverse psychiatric and psychosocial outcomes. An expanding evidence base is available to guide efficacious treatments for adolescents with problematic marijuana use. The majority of evidence supports motivational enhancement, cognitive behavioral, and family therapies, while new findings suggest that contingency management as well as the pharmacotherapy N-acetylcysteine may enhance abstinence outcomes. More work is needed to optimize strategies to prevent and treat cannabis use disorders in young people, especially in an evolving public policy setting in which adolescents may be more prone to view marijuana favorably and initiate use.

PREVALENCE, EPIDEMIOLOGY, AND POLICY CONSIDERATIONS

Marijuana is the most commonly used illicit substance in the US and the world. Onset of use typically occurs in adolescence, and the peak prevalence of use is among young adults. Recent trends among young people suggest that perceptions of marijuana-associated risks are decreasing, though rates of use may be stabilizing or even slightly decreasing after prior notable increases.¹ Youth are more vulnerable than adults to adverse consequences of marijuana use, and more likely to develop cannabis use disorders.² Marijuana is the most common primary substance of use among AYAs entering substance use treatment.³ Recent key prevalence findings are outlined below.

Adolescents

Monitoring the Future (MTF) 2014: Past-year use of marijuana was 11.7%, 27.3%, and 35.1% in 8th, 10th, and 12th graders, respectively. Lifetime (ever) use was 15.6%, 33.7%, and 44.1%, respectively, by grade, while past-month use was 6.5%, 16.6%, and 21.2% and daily use was 1.0%, 3.4%, and 5.8% by grade (www.monitoringthefuture.org).
Youth Risk Behavior Survey (YRBS): In the 2013 YRBS survey, 40.7% of 9th to 12th graders have ever used marijuana, with a prevalence of 39.2% in females and 42.1% in males. The proportion reporting ever use of marijuana was 36.7%, 46.8%, and 48.8% in White, Black, and Hispanic students, respectively, and by grade, 30.1%, 39.1%, 46.4%, and 48.6% for 9th through 12th grades, respectively. (http://www.cdc.gov/HealthyYouth/yrbs/index.htm)
National Survey on Drug Use and Health (NSDUH): In the 2013 NSDUH study among 12- to 17-year-olds, the prevalence of use in past month was 7.9% in 2011, 7.2% in 2012, and 7.1% in 2013 (http://www.samhsa.gov/data/sites/default/files/NSDUHresultsPDFWHTML2013/Web/NSDUHresults2013.pdf).

Young Adults and College Students

MTF 2013: Since 2000, the annual prevalence of marijuana use among college students reached a recent peak prevalence of 36% in 2001, declined to 30% in 2006, and then increased to 36% in 2013. Noncollege young adult peers showed comparable changes over the same time interval. The annual prevalence rates for both groups were comparable across this interval (www.monitoringthefuture.org).
National College Health Assessment (NCHA) 2014: Among this national survey of college students, 61% have never used marijuana, 20.7% used but not in last 30 days, and 18.3% used in the past month, with 2.6% reporting daily use (www.acha-ncha.org).

While the US Drug Enforcement Agency classifies marijuana as a schedule I drug (high potential for abuse, no currently accepted medical use in the US, and no accepted safety for use under supervision by a physician), several states have proceeded with policy changes to legalize/decriminalize marijuana for medical and/or recreational purposes. These changes may potentially present unintended downstream effects relevant to youth,⁴,⁵,⁶ though more work is needed to clarify these issues.⁷,⁸

PREPARATION AND USE

Human use of marijuana, derived from the plant Cannabis sativa, dates back to at least 2700 BC. The main psychoactive component of marijuana is Δ⁹-tetrahydrocannabinol (THC), which is present in varying concentrations across parts of the plant. Marijuana is composed of the dried seeds, stems, leaves, and flowering top of the plant. This preparation typically contains 0.5% to 5% THC, while hashish, a dried cannabis resin, contains 2% to 20% THC and
an oil-based hashish extract contains 15% to 50% THC.⁹ With advances in cultivation and preparation, the THC concentration in marijuana has increased significantly in recent decades.¹⁰

Marijuana may be smoked, vaporized/inhaled, or ingested. Smoking is the most common method of administration, and this results in the most rapid delivery of THC to the brain. A marijuana “joint” is composed of dried cannabis rolled into cigarette paper, whereas a “blunt” is a larger portion rolled into a hollowed/emptied cigar. Some users combine tobacco with marijuana when smoking joints or blunts. Marijuana is also often smoked in a pipe, also called a “bowl,” or a water pipe, known as a “bong.” Individuals seeking a higher THC concentration often smoke hashish using similar methods. Marijuana is commonly ingested in the form of brownies or other food products, though this leads to slower absorption and more delayed/gradual psychoactive effects than smoking/inhaling. Given the variety of products/routes of administration, the broad range of THC concentrations, and the frequency of sharing with a group, standardized quantification of marijuana use is considerably more challenging than for many other substances (e.g., cigarettes, alcohol).

Slang terms for marijuana and its various preparations are too numerous and geographically variable for an exhaustive review in this chapter, though “weed,” “pot,” “bud,” “grass,” “herb,” “dope,” and “Mary Jane” are particularly common. Slang terms reflecting potency often range from “schwag” (low potency) to “kine bud” (high potency). Recent preparations of highly concentrated cannabis may be referred to as “dabs,” “wax,” or “shatter.”

PHARMACOLOGY AND NEUROBIOLOGY

Marijuana is composed of at least 60 distinct cannabinoid compounds and about 500 total chemical constituents. The relative concentrations and potencies of these ingredients vary significantly across strains and preparations. Cannabinoids exert their effects via binding to cannabinoid receptors, which are widely dispersed in the central and peripheral nervous system. To date, two cannabinoid receptors, CB₁ and CB₂, have been well characterized, and they, along with endocannabinoids (including anandamide and 2-arachidonoylglycerol), comprise the endocannabinoid system, which plays a modulatory role in a number of physiologic processes. While our understanding of the endocannabinoid system is likely in its infancy, it is known to be involved in cognition, memory, mood, appetite, immune function, motor coordination, and pain sensation.

THC, the primary psychoactive component of marijuana, binds to CB₁ and CB₂ receptors. Its potency, when delivered via smoked marijuana, is far greater than the analogous endocannabinoids. Activation of CB₁ receptors in the brain leads to downstream effects on several neurotransmitters, including dopamine, conveying marijuana’s psychoactive and reinforcing effects.

THC is highly lipophilic and is rapidly distributed into tissues. While smoked marijuana leads to rapid uptake of THC into the central nervous system, most of the THC administered remains in the periphery. THC is primarily metabolized by the liver, and a number of active and inactive metabolites have been identified. The rate of excretion of THC is slowed by its propensity to deposit in lipid-rich tissues. THC metabolites are typically detectable in urine for 1 to 3 days after acute use, and may remain detectable for weeks in chronic/heavy users.¹¹

Among other cannabinoids in marijuana is cannabidiol, which is now the subject of significant interest for potential therapeutic (e.g., anticonvulsant, anxiolytic, and antipsychotic) effects. Strains of marijuana with higher ratios of cannabidiol to THC appear to be associated with reduced likelihood of memory impairment and psychotomimetic effects. However, many strains have been developed with particularly low ratios of cannabidiol to THC, given many users’ preference for stronger psychoactive effects associated with high-dose THC.

Behavioral and Physiologic Effects

Acute Effects

Immediate/short-term effects of marijuana vary significantly based on its potency/constituency, the user’s expectations, the setting of use, the user’s marijuana naivety versus experience, the amount used, and the route of administration. Psychoactive and physiologic effects are detectable within 30 minutes of smoking/inhalation and typically last for 2 to 3 hours, whereas effects of marijuana ingestion are detectable within 90 minutes and last 6 or more hours. Marijuana is most often used recreationally to achieve a mild euphoria or “high,” to experience pleasant distortions of ordinary experiences, and to facilitate social interactions. Naïve users are more likely to report adverse acute experiences, including anxiety/panic as well as psychotic symptoms.

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