(Editor’s Note: This is the latest in a series of articles about marijuana use in Colorado.) 

One of the first things to consider when evaluating public health impacts is how widespread or prevalent a health issue is. Marijuana use has always been on the radar in terms of health and safety, but legalization has magnified that conversation as more than half of U.S. states have legalized medical marijuana and eight states plus the District of Columbia have legalized retail sales of marijuana.

In 2015, 22.2 million Americans had used marijuana in the past month, or roughly 8 percent of the U.S. population. In the state of Colorado in 2015, surveys show past-month use between 13 percent and 17 percent, which is significantly higher than the U.S. rate. In terms of youth across the U.S., 36 percent of high school seniors say they had used marijuana in the prior year, 23 percent had used in the past month and 6.5 percent used daily or nearly daily. By 2016 in Colorado, there were more legal, medical and retail marijuana dispensaries (940 total) than there were McDonald’s restaurants (202) and Starbucks shops(322).

The prevalence makes understanding the health impacts particularly important. Yet it is inherently difficult to tease out health impacts for two reasons. One, the illegality of marijuana up until relatively recently has made data collection challenging. Two, there is possible reverse causation in many of the studies that have shown negative impacts, especially on mental health: Does marijuana use increase mental health disorders or are people predisposed to mental health disorders more likely to regularly use marijuana? The aim in this article is not to promote or reject theories, but only to present relevant health information, especially as it relates to recreational use. Marijuana use for chemotherapy patients, seizure-related disorders and as a substitute for opioid pain killers is generally accepted by the medical profession and is a somewhat separate issue. Nonetheless, the prevalence of use makes it particularly important to disseminate the reliable information we do have, and the legal status of recreational marijuana in our state provides a need to do so.

To begin, brain imaging shows that marijuana primarily affects the hippocampus, a brain area responsible for memory formation, and the amygdala, responsible for emotions, survival instinct, memory and reward system receptors. We know long-term users of marijuana have reduced volumes in both of these regions of the brain and there is less activity in those regions even 28 days without using marijuana. We also know that the hippocampus and amygdala undergo prominent developmental changes throughout childhood and adolescence, which likely explains why early users of marijuana show more significant and negative outcomes than those who begin using in adulthood. A large, longitudinal study in New Zealand found that persistent marijuana use during adolescence was associated with a loss of six to eight IQ points by mid-adulthood, and this was equally true for adults who had quit using, as well as those who continued using. Again, these results are not conclusive, because the lower IQ may be caused by other factors inherent to young people who choose to use marijuana. It is notable that individuals who began using marijuana heavily in adulthood did not appear to have any loss in IQ.

Given the brain impacts, one area that merits greater attention is the possible correlation between the increased potency of tetrahydrocannabinol, or THC, and youth suicides (see graphs). Given the effects of marijuana particularly on the adolescent brain, the psychotropic properties of THC and the self-reported increase in suicide ideation, the alarming increase in youth suicides might be linked to increases in THC potency. Correlation is not necessarily causation, but the possibility of association certainly calls for further study.

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For both adolescents and adults, some research suggests marijuana use increases the chances of developing psychotic disorders including schizophrenia when an individual has a genetic predisposition for the disorder. Although research continues on this topic, it is evident that for individuals who carry a specific gene, there is a seven-fold increased risk of developing psychosis, or loss of reality, when they use marijuana. A user also has to carry a specific gene in order to be at increased risk that marijuana use will trigger or worsen schizophrenia. About 1 percent of the population has schizophrenia and even fewer carry that specific gene. However, there are two important points to consider. One, for all users, in high enough doses, marijuana causes psychosis, and there is mounting evidence that psychosis itself is harmful to the brain and can increase the probability of triggering a psychotic disorder. Another point to consider is that the U.S. already has a high prevalence of mental health disorders and at the same time, a low availability of providers to treat mental illness.

The circulatory system is also impacted by marijuana use because an individual’s heart rate is elevated for up to three hours after smoking. The increased potency in edibles magnifies this effect. There are numerous studies that show the risk of a heart attack during the first hour after smoking marijuana is almost five times the usual risk. Most healthy individuals can easily withstand an increase in their heart rate — although edibles in particular can cause a heart rate to double. This increase in beats per minute is too taxing on the circulatory system of some individuals who have either diagnosed or undiagnosed heart conditions.

In terms of marijuana possibly being a “gateway drug,” studies are inconclusive. It is true that marijuana causes cross-sensitization, meaning that the effects of other drugs (including alcohol) are heightened when the brain has already been exposed to marijuana. This would suggest that marijuana is a gateway drug; however, reverse causation may again explain this phenomenon. Marijuana users may be predisposed to taking drugs, and marijuana may simply be the easiest drug in terms of access and cost.

There are longitudinal studies that have shown less optimal life outcomes for regular marijuana users, such as lower educational attainment, lower income, lower life satisfaction and increased prevalence of anxiety and depressive disorders. It is possible that the above-mentioned impacts on the brain do provide a plausible biological explanation.

It is also possible that at least some of the less optimal life outcomes are due to the downstream effects of (particularly early) use of marijuana and its impact on school performance, high school completion and in some cases, even incarceration related to marijuana possession and use. Perhaps the unfavorable, long-term impacts are partially due to the biological impacts, but also due to the social outcomes associated with early use, which young adults can carry with them throughout adulthood (e.g. absence of a high school diploma).  In either case, there are associated long-term social and economic costs.

In the short term, it is also important — and easier — to assess health care costs. A comprehensive, retrospect analysis was done of Colorado hospital admissions and emergency department (ED) visits with marijuana-related billing codes and calls to regional poison control (RPC) centers. Results show an increase in hospitalizations: From 2000 to 2015, hospitalization rates with marijuana-related billing codes increased from 274 to 593 per 100,000 admissions (up 116 percent). The prevalence of mental illness among ED visits with marijuana-related codes was five-fold higher than the prevalence of mental illness without marijuana-related codes comparing the same two time periods. In 2014, the first year of commercially available recreational marijuana, calls to RPCs increased 79.7 percent.

If I take off my public health hat and step back from these negative health repercussions, I do acknowledge that not unlike alcohol, limited and responsible adult use of marijuana does not appear to be that different than responsible drinking. The negative impacts of both substances are very dose dependent. The question remains: Can we successfully regulate use and potency and also reduce or eliminate childhood and adolescent use given the deleterious impacts on the developing brains? Is it wise to readily expose our communities to even more sources of costly health problems and increased safety issues? Since our state has already gone down the path of legalization, what is certain is the need for a holistic analysis that not only focuses on economic benefits, but one that also incorporates and quantifies the associated health and safety costs of increased access to and use of marijuana.

Tatiana Bailey is the director of the UCCS Economic Forum. She can be reached at tbailey6@uccs.edu. For a complete listing of references, please go to: uccseconomicforum.com/publications_media.shtml.