A closer look at marijuana and its potential to exacerbate cognitive problems

By Mary Ellen Aldrich and Cara DeRose


As of January 2017, recreational marijuana is officially legal in Maine for those who are twenty-one and older. Although recreational marijuana’s previous illicit status never deterred people from using it, people can now smoke marijuana without the usual obstacles of accessibility and unlawfulness (so long as a person does not possess more than two-and-a-half ounces). 

Experts and civilians alike generally agree marijuana is not the gateway drug staunch opponents of its use make it out to be, but research has emerged that heavy use can potentially pose cognitive risks, particularly for those who have mental health conditions, such as schizophrenia, and those whose family histories predispose them to mental health conditions.

Rikki Miller, a research psychologist and lecturer at USM, has studied the effects of marijuana on the brain. From 2007 to 2010, Miller conducted research on the effects of cannabinoids (using analogs of THC created by chemists) on the attention and memory of rats, as well as on their eating habits, at Edinboro University. She spoke to the Free Press about what she has gleaned from her research.

“Much of the pros and cons publicized on this issue often enhance the facts that suit the argument [either side] wants to support,” Miller remarked. “Marijuana is neither a deadly, dangerous drug nor a harmless plant.”

In regards to its use among those with mental health conditions, studies and anecdotal testimonies point in both directions: that marijuana is helpful and provides relief to those with mental health conditions, and that heavy marijuana use can also lead to the exacerbation of symptoms and to cognitive impairment. Because this debate could continue endlessly, Miller has recommended ignoring the anecdotal testimonies and, instead, looking at the facts.

“The major documented risk of using marijuana,” Miller said, “is its impact on the brain’s ability to store long-term memories while under the influence.”

According to Miller, while under the influence of marijuana, the brain’s ability to form long-term memories is impaired. This impairment is due to marijuana’s impact on the hippocampus, which is the region of the brain responsible for long-term memory formation and the only place in the brain where new neurons are formed. Heavy marijuana use can impair the formation of long-term memories and negatively impact neurogenesis, or the growth of new neurons. When neurogenesis is inhibited, an individual’s ability to learn suffers.

With that in mind, research has shown that heavy marijuana use, particularly during adolescence, can potentially aggravate mental health conditions, with one study involving an Australian cohort showing a connection between marijuana use and an exacerbation of symptoms among those genetically predisposed to develop schizophrenia. Another year-long study, involving 69 schizophrenia patients who occasionally used marijuana and 24 who were heavy marijuana users, showed a correlation between heavy marijuana use and psychotic relapse. 

Additionally, a study found that, within certain genetic subgroups, schizophrenia patients who used marijuana frequently had smaller frontotemporal white matter volumes than schizophrenia patients who used marijuana infrequently, suggesting a correlation between heavy marijuana use and increased cognitive impairment among schizophrenia patients with certain genes.

Yet while this research indicates that it is possible that, in some cases, marijuana can exacerbate symptoms and lead to cognitive impairment, a sufficient number of studies have not been conducted, with large enough sample group sizes, to conclusively support or disprove this.  

“There are multiple factors to consider,” Miller said, “such as the reverse that individuals [who] have a predisposition to mental illness could be more likely to use marijuana, and that the use of marijuana can interact with medications used to treat psychological disorders or other medical conditions.”

Marijuana is also not always the cause of symptoms but can be, rather, a source of alleviation. Those with mental health conditions use marijuana to mitigate symptoms, sometimes in conjunction with their medications. Some of these self-medicating individuals find relief in the relaxing effects marijuana imparts. However, those taking stimulant drugs, such as Adderall or Concerta, for ADHD/ADD would benefit from knowing that marijuana has the opposite effect of their medications, so using marijuana and stimulant drugs concurrently is counterintuitive.  

Another related concern for anyone using marijuana is that its use can result in psychological addiction. Psychological addiction is different from physical addiction. When someone is physically addicted to a substance, their body has adapted to the presence of that substance, and without it, the individual experiences withdrawal symptoms. With psychological addiction, there is a perceived need for the substance.

“Marijuana is psychologically addictive, causing people to think they can not function without the substance,” Miller said.“’I use it to sleep,’ ‘I use it to calm my anxiety,’ ‘It is the only thing that gets rid of my headache,’ et cetera.”

This psychological addiction to marijuana can lead to more frequent use, resulting in further inhibition of long-term memory formation and neurogenesis. The long-term effects of marijuana on brains of adolescents and young adults could pose a threat to brain development, particularly among those who have mental health conditions, but more research will need to be done before a clearer connection can be made.