Potential health risks of recreational marijuana

Editor’s Note: Community Word ran an editorial in our September 2014 edition advocating for the legalization of recreational marijuana, not because we need more mind-altering drugs but because criminalization disproportionately impacted African Americans even though use is equal between whites and Blacks. Unjust criminalization ruined lives. Marijuana is now regulated in Illinois like alcohol and remains illegal for youth. This article is not reopening the debate over legalization but informing readers of harmful health effects from usage.


Medical information regarding marijuana is still incomplete but has rapidly increased over the past 25 years. This article reviews what is known today about the adverse effects of using marijuana. We expect the research will continue to mount.

We divide adverse effects of marijuana use into two groups: short-term use effects that can occur every time a person uses marijuana and long-term or heavy use effects. Frequent, heavy or long-term use clearly results in more severe consequences than does occasional use. What constitutes heavy use is variously defined. One definition is use of more than twice a week. But a person who uses marijuana once or twice a week can clearly experience some of the more severe consequences if they carry on that usage level for months or years.

Marijuana contains many different compounds, probably on the order of 100 to 200. The effects of most of these compounds are not well understood. The best understood of the compounds are tetrahydrocannabinol (THC) and cannabidiol (CBD). The compound that gets a person high is THC. It is also the compound that causes most of the known negative effects of marijuana.

Effects of short-term use

Impaired short-term memory: Marijuana use causes a decreased ability to learn probably lasting several hours.

Impaired psychomotor skills including driving: Just as alcohol usage impairs driving ability, the same is true for marijuana usage. The effect lasts at least several hours though there are some studies suggesting impairment may persist for 24 hours or longer. Use of both marijuana and alcohol at the same time appears to have a synergistic negative effect on driving skills; usage of both impairs driving much more than the use of either alone.

Altered judgment: Poor decisions are more likely when under the influence.

Psychosis and paranoia: Psychosis is probably the most consequential of the short-term effects. The risk is higher with use of high amounts of THC. A single psychotic episode can be a life-changing event. Paranoia is a symptom of psychosis that some users experience. Not everyone who experiences paranoia will have a psychotic episode but anyone who experiences paranoia should avoid using more during that session and perhaps even longer term.

Effects of long-term or heavy use

Addiction: Although there remains some controversy about this topic in the lay public, there is no controversy within medicine. THC is an addictive substance. Addiction is a complex disease that can be characterized by compulsive use of a substance and continued use despite negative consequences. This is true whether the addictive substance is opioids, alcohol or marijuana.

All addictive substances have a common effect of increasing dopamine in the brain’s pleasure center, the nucleus accumbens. THC is known to act in the same way and to cause the same drug seeking behavioral changes that are seen with all other addictive substances. Just as with other addictive substances, young people under age 25 are by far the most prone to developing addiction.

With the young, about 1 of every 6 who uses marijuana will develop addiction. Particularly for a young person, addiction can be life changing as it takes focus away from the things they need to achieve and do to establish themselves as an adult, e.g., education, job seeking and advancement and social relationships.

Hyperemesis: Although marijuana is used as an antiemetic, an agent that decreases nausea and vomiting, many people who use marijuana regularly over a long period develop a severe persistent vomiting condition called cannabinoid hyperemesis syndrome (CHS). Hyperemesis is now being seen regularly in hospital emergency rooms in states where marijuana is legal. The condition can be serious resulting in severe dehydration and electrolyte imbalances. At least three deaths have resulted in the United States and Canada from this syndrome, all in people who continued to use marijuana despite developing CHS. A person who develops CHS needs to stop using marijuana completely.

Altered Brain Development: Critical areas of the brain are not fully developed until at least age 25. The alterations in brain development that occur with marijuana use are still being researched, largely through the use of magnetic resonance imaging (MRI). The severity of the changes is incompletely understood. The effect is probably not peculiar to marijuana but likely occurs with use of any addictive substances.

Poor educational outcome: The best available data indicates that people who regularly use marijuana during high school and college years fail to achieve the educational level that non-users do.

Increased risk of chronic psychosis, particularly schizophrenia: Chronic psychosis means that the sufferer has recurrent bouts of psychosis. Chronic psychosis is a profoundly life-changing diagnosis. Regular use of high potency marijuana raises the odds of developing schizophrenia by as much as 6-fold. Perhaps the best definition of high-potency is marijuana that contains 10% THC or more. For those using less potent marijuana regularly, the risk is also increased, probably in the 2- to 4-fold range.

The list of adverse effects given above is meant to include effects that occur most commonly, and which are the best understood. It is not exhaustive. For example, effects on lung and heart function have not been covered. Two other issues that should be briefly discussed are the use of marijuana in pregnancy and the question of “gateway effect.”

Use of marijuana by pregnant women has greatly risen over the past several years. THC crosses the placenta so when a woman smokes or ingests THC, the fetus is also exposed. Use during pregnancy is known to result in low birth weight and likely increases the odds of premature birth. THC may affect fetal brain development, and that can result in adverse lifetime outcomes. Women who are nursing and using marijuana should also be aware that THC is present in their breast milk. The effects of THC ingestion by infants is largely unknown.

The gateway effect posits that when marijuana is used by an individual, the user in some way becomes sensitized to other addictive substances as well, resulting in an increased risk of that individual becoming addicted not only to marijuana, but also to one or more other addictive substance. The 2017 report of the National Academy of Sciences entitled “The Health Effects of Cannabis and Cannabinoids” concluded that the gateway effect likely is real.

The public should realize that the gateway effect probably is not only an issue for marijuana but for all addictive substances; it is likely that exposure to any of these substances primes the brain in such a way that other addictions become more likely. This priming effect is of most concern for adolescents and young adults.

It is too early to correlate ER admissions to legalization of recreational marijuana, but Dr. Robert Wolford, emergency physician at OSF Saint Francis Medical Center, said over the past few years, he has seen a higher positive rate of drug screens for marijuana. He has seen a definite increase in patients with intractable vomiting due to the cannabinoid hyperemesis syndrome. He says that when patients are told that their vomiting is related to their marijuana use, they often express disbelief, saying that marijuana use helps their symptoms. He has noticed an increasing number of psychiatric admissions though he is unsure whether that is related to marijuana use.

In conclusion, marijuana is a complex product containing a myriad of chemical compounds. There are many concerning negative effects. People at highest risk are those under 25. It is important that the public be aware of these effects so that people can make informed decisions about personal use both by themselves and their families.

Raymond E. Bertino, M.D., was an honors graduate of University of Michigan Medical School. He practiced vascular and interventional radiology in Peoria for 28 years, retiring 2.5 years ago. He is a clinical professor in radiology and surgery at the University of Illinois College of Medicine, Peoria. Since retirement, he has been working on substance abuse issues. He is a member of the Board of the Illinois Society of Addiction Medicine.

Kirk Moberg, M.D., Ph.D., is a clinical professor of internal medicine and psychiatry at the University of Illinois College of Medicine. He has practiced in the field of addiction medicine for 25 years and is the former executive medical director of the Illinois Institute for Addiction Recovery. Dr. Moberg is board certified in internal medicine and addiction medicine and is a member of the board of the Illinois Society of Addiction Medicine.

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