By: Nicole Evans-Turk, Pharm.D Candidate 2022
Mentor: Amy Tiemeier, Pharm.D., BCPS
With the growing medicalization of marijuana and legalization of recreational marijuana, information on the medicinal value of the plant as well as risks of using marijuana are needed. With any drug, there are risks and benefits to its use. Marijuana is the most used drug by adolescents.1 With strains of marijuana becoming more potent and with new inventive ways to consume it, risks may be more significant in adolescents and have impact into adulthood. This article will discuss the potential risks for adolescents who use marijuana, with marijuana being defined as the whole plant that is smoked or ingested.
Adolescents have more access to marijuana now than they did even 10 years ago. While it is available for adults over 21 in some states, 11-23% of recreational outlets may sell to minors.2 Marijuana has also commercialized and is advertised in newspapers and on billboards. While more research is needed to determine whether the exposure to marijuana advertisements influences adolescents to start using marijuana before adulthood, at least one study has found a positive correlation between ad exposure and perceived ease of access for teens.3 Annual prevalence of marijuana usage among high school seniors increased from 22% to 36% over the decade from 2004 to 2014.1 In a 2020 survey, 19.8% of high school age people report using marijuana in the past month4. With the increased usage, there are effects on the brain that affect more and more people as they mature into adults. A review of adolescent brain development and marijuana is important given these facts.
Adolescence is a critical period for neurodevelopment and it is characterized by dynamic changes in the mesolimbic dopamine pathway.5 The echocannabinoid (eCB) system reaches peak expression and activity during adolescence. The eCB system acts as a regulator in the reward pathway and also plays a role in determining vulnerability to drug addiction. The CB1 (cannabinoid 1) receptor and eCB ligand N-arachidonoylethanolamine (AEA) both have peaks in expression during adolescence as well. AEA is regulated by the enzyme fatty acid amide hydrolase (FAAH), which is expressed in brain regions that are implicated in the reward and addiction pathways. Activation of this system gives adolescents more intense effects from marijuana than adults usually experience due to the greater expression of AEA and CB1. With prolonged and repeated activation, adolescent brains have a higher risk of a psychological addiction through these pathways5. National surveys have found that youth who engaged in marijuana use in later teen years were less likely to develop substance use disorders compared with those who started earlier, which correlates with the changes in the eCB system in adolescents compared to adults.4
Marijuana-related effects on white matter and grey matter can have widespread implications for brain development, such as impairments in daily functioning.1 White matter in the brain is the communication pathways between areas of the brain and grey matter is the structures where the processing is done. Grey matter changes for marijuana users during adolescence is still being studied, but a study in 2010 found users to have decreased right orbital prefrontal cortex volume compared to non-users. The prefrontal cortex controls the executive functioning skills such as planning and decision-making. The decreased volume of the prefrontal cortex correlates to lower executive reasoning skills and executive dysfunction. The volume reduction is positively correlated with the age in which the person started using marijuana, with the most changes being seen in those who started using at a younger age.1 Findings in white matter between adolescent marijuana users and non-users also differ. An increase in mean diffusivity in the prefrontal fiber bundles of the corpus callosum is also found in adults who use marijuana heavily and started as an adolescent. These fibers are what allows the prefrontal cortex to receive information and process it. The effects of these changes to the grey and white matter of the brain are theorized to negatively affect executive functioning skills but the full extent is still being studied.
A common theory is that using THC (tetrahydrocannabinol) in adolescence can contribute to mental disorders in adulthood. In a study where they used a questionnaire to assess whether cannabis use was linked to increased psychiatric symptoms, respondents who met criteria for cannabis use disorder were more likely to report having experienced hallucinations or paranoia. Participants who also met criteria for depression were also more likely to experience hallucinations or paranoia with use of cannabis.6 Adolescents who use marijuana are more likely to misattribute meaning to life events, which can implicate symptoms of psychological disorders. Cannabis use is considered an environmental risk factor in the development of cognitive dysfunction and psychotic disorders.5 While psychological disorders correlate with adolescent marijuana use, there is not enough data to link the two as cause and effect. There could be another conclusion that adolescents with psychological disorders may be self-medicating with marijuana.
The conclusions of a meta-analysis show that executive functioning seems to be more impaired in frequent users who are adolescents than in frequent users who are adults. Most age related effects seem to be prominent among heavy and dependent users compared to those who may use sporadically. In addition, adolescents may also have more cravings after marijuana intoxication compared to adults.6 Marijuana use was associated with declines in neural connectivity over time, which correlate to adverse effects on IQ and executive function.4 Executive function refers to decision-making, planning, self-control and organization. This confirms that there are physical changes in the adolescent brain that happen with frequent marijuana usage. The full extent of how the brain and cognitive abilities are affected needs to be researched further.
In conclusion, pharmacists should be aware of the decisions that adolescents make to use marijuana. With new data coming out that confirms there are neurodevelopmental changes that can happen with prolonged marijuana use in adolescents, children and caregivers should be educated on the potential long-term effects of using marijuana during adolescent years. A pharmacist who specializes in pediatrics or psychiatry should also continue to keep up to date on new research as it comes out about the eCB system and its mechanisms in relation to marijuana.