Vivek C. Shah, M.D., Murali K. Kolikonda, M.D., Suneela Cherlopalle, M.D., Steven  Lippmann M.D.

Okay, marijuana is being legalized in many places across this country. Lots of people smoke pot. Some of them may have the impression that governmental legalization of this drug implies safety. What should you tell your adolescent patients?

Cannabis is one of the most widely used drugs in the world. Because of legalization in several states and decriminalization campaigns, many people, especially adolescents, might erroneously misinterpret this as a sign that the drug is harmless. However, it has profound adverse effects on the brain, especially for cognition.Reportedly, nearly half of all high school seniors smoke marijuana at least occasionally and 5% do so regularly, with adolescents and young adults the predominant population using it.

Tetrahydrocannabinol (THC) is a psychoactive constituent of marijuana. When smoked, THC rapidly passes from the lung into the blood stream for body-wide distribution. THC exerts a prominent effect on cannabinoid receptors in the central nervous system, mainly in the hippocampus, amygdala, cerebellum, pre-frontal cortex, and striatum. Receptor activation results in increased dopamine release and produces psychotropic effects.
        
Adolescence is a critical time for neuronal development of the brain; smoking marijuana has negative implications for cognition.  Exposure to marijuana during this maturational period may impair cerebral function. This affects the brain at hampering attention, executive performance, and the intellectual aspects of learning and memory. Regular marijuana smokers perform less well on tests of attention, non-verbal memory, learning, visuospatial activity, speech fluency, and exhibit lower intelligent quotient (IQ) scores; from adolescence to adulthood they evidenced a 6-point decline in IQ scores. Females appear to be more vulnerable to the neurocognitive compromise than males. This is related to differences in hormone and receptor distribution.

Among more frequent marijuana users, abnormalities in cerebral structure are documented.  Brain imaging studies document gray matter damage, especially in the prefrontal regions important to cognitive performance. The neuropsychological impairment can also create major dysfunction at activities of daily living.
 
The major concern is for adolescents with developing brains, and even for individuals up to 25 years of age. They are the most vulnerable group and also the most frequent users. Dangerousness begins with as little as once a week exposure. It is important to explicitly provide this awareness to younger persons.

This prompts physicians to provide guidance and explicit warning to younger current or potential marijuana smokers and their families. It is an important clinician task to educate people about these risks. Doctors also have a public health responsibility to impart this information to the wider public through education, publication, and discussions at schools or governmental bodies.

The intellectual impairments induced by marijuana do not appear to be as dangerous to adults. Such drug exposure is not as deleterious to the already developed brain. Thus, cognition is less at risk and there are fewer healthcare admonitions against its use by persons over age 25 years. Marijuana and/or THC-containing products utilized for nausea, glaucoma, pain, or relaxation therapies may not impair brain function for these older adults and is therefore of less concern.
             
Suggested readings
1.    Meier MH, Caspi A, Ambler A, et al. Persistent cannabis users show neuropsychological decline from childhood to midlife. Proc Natl Acad Sci USA 2012; 109(40): E2657- E2664
2.    Jacobus J, Bava S, Cohen-Zion  M, et al. Functional Consequences of Marijuana Use in
Adolescents. Pharmacol Biochem Behav  2009; 92(4): 559–565