Pulling Weeds: clearing the smoke on Marijuana’s effects on the thinking and emotion

Several days ago, I was talking to two recent college graduates about choices, particularly those involving what people put into their bodies. In that context, the conversation meandered from alcohol through nicotine to marijuana – all the way to the opioid crisis; however, most of our dialog centered on recreational marijuana. Their questions were quite fascinating in such a way that I took the liberty to summarize our content in this brief blog.
It appears that the majority of Americans consider marijuana to be harmless; perhaps to illustrate this point, Andrew Scheyer (January/2019) noted that 70% of women in the USA believe that there is “slight to no risk of harm” in using cannabis during pregnancy, with 7.5% of 18-25 year old women reported smoking during gestation. The conversation on marijuana is not about some best kept secret that no one knows or talks about; the questions are related to what, if any, concerns might be worth further discussion in relation to its use. Researcher C. S. Wu and colleagues (2010) pointed out that there are at least 108 cannabinoids that can bind to receptors in brain, prompting the journal called The Scientist (July/August 2017) to state, “Your Body is Teeming with Weed Receptors.” Animal and human studies have long established that our brains have several cannabis receptors; therefore, the question is not whether or not marijuana affects the brain but what potential risks may be present and for whom. Our brains have receptors for opioids, depressants, and hundreds of other agents, but what matters is how these substances are used. In longitudinal studies of mothers who smoked marijuana once per week during pregnancy, results showed negative outcomes in neonates, early childhood, adolescence, and adulthood; this data mirrored findings from animal models (i.e., rodents). Concerns included increased anxiety, depression, aggression, impulsivity, delinquency, hyperactivity, antisocial behaviors, and opioid seeking tendencies. On the other hand, there were problems with attention, memory, verbal reasoning, and alterations to dopamine receptors. After we reviewed this point, both millennials chuckled and said that was not a concern of theirs at all and they correctly added that only a few people would be at risk for such difficulties.
In a systematic review on medical marijuana laws (MML) and adolescent use of the substance, Aaron Sarvet and his associates (2018) commented that MMLs are not correlated to recreational weed smoking in 28 states with such laws. The authors admit that some individuals may use marijuana without serious consequences; however, the cite numerous studies that highlight impaired functioning in the form of vehicular accidents, psychiatric symptoms, and addiction. Sarvet added that heavy use has been strongly associated with altered brain development and decreased education attainment, and it is quite likely that that these two concerns may be related.
The question of brain development was the focus of studies conducted by Medina and colleagues (2007&2010) wherein they found anatomical problems in the areas that control learning, attention, memory, and higher order thinking (i.e., executive functions). Further, the combination of marijuana use, and alcohol consumption was related to cognitive impairment in numerous domains (Jacobus 2018) as a function of compromised brain integrity. When researchers drilled down in efforts to identify why some young and older adults showed cognitive and behavioral problems when there was a history of marijuana use, they found one key variable: age at first exposure (Schuster et. al., 2016). That is, problems with brain anatomy – hippocampus, prefrontal cortex, anterior cingulate, basal ganglia, cerebellum, etc.—and cognitive outcomes – attention, learning, memory, executive functions, etc. – all turn on one critical variable, the age of the individual when they started using marijuana.
According to research neuropsychologist Staci Gruber, Negative outcomes (e.g., lower IQ scores) were consistently associated with marijuana use prior to the age of 16 years. She has written extensively to this fact, demonstrating that earlier/younger onset users were invariably at a disadvantage when compared to peers who used marijuana after about 21 years of age. The author was not advocating for use of marijuana as much as she was providing possible reasons for differences in outcomes among users. At this point in our conversation, the two young adults asked what the bottom line is on marijuana and risk of use.
As Dr. Gruber states, “today’s weed is not what your grandparents smoked in the 1960’s;” the strains of what’s smoked are simply not well understood. The bottom line is that marijuana exposure to a young and developing brain is a risky decision; further, conservative estimates would suggest that our brain are not really done maturing until at least early 20’s into our 30’s. A word about medicinal marijuana: one has to consult with their primary care provider before introducing any new substance to their body for treatment. For certain CBD has been found to be helpful in some instances, whereas THC in recreational marijuana is of dubious – if any – curative, medical benefit. It would seem that we are still in the infancy of knowing fully well what marijuana means to the body, and claims about risks and benefits should be informed by legitimate scientific inquiry. It was at this point that my two young adult colleagues shrugged their shoulders and hinted they simply wanted to enjoy a summer break free from anything academic.