Next month, 10 states will have some form of marijuana legalization on the ballot. In Nevada and Massachusetts, for example, the new laws would allow anyone 21 years of age or older to possess, use and grow marijuana.
Proponents of these measures argue that the social and economic advantages of marijuana legalization outweigh the health risks. But the health effects of marijuana use are significant and underreported — and legalization leads to an increase in its use.
A vast and growing medical literature describes marijuana’s ill health effects. They include increased chronic cough and wheezing in long-term marijuana smokers as well as “marijuana lung” in young patients, which can cause lung collapse. Emergency physicians are familiar with cannabis hyperemesis syndrome, in which users develop severe vomiting. Marijuana use increases the risk of stroke and spontaneous brain hemorrhage, even among young patients. It can depress the immune system, lead to infections, decrease sperm count, impair ovulation and affect the placenta in pregnant mothers.
Marijuana smoke causes cancer in animal studies as well as DNA mutations in lab tests. It contains several of the same cancer-causing chemicals found in tobacco smoke, at up to 50 percent higher concentrations, and with three times the tar per cigarette. THC, the primary active ingredient in marijuana, and related compounds are secreted in breast milk. Perhaps most important, these compounds — marijuana smoke contains more than 60 of them and 400 chemicals overall — act on the nervous system to cause not only the altered mental state that users expect, but also many harmful neurological effects.
Marijuana users have been found in several studies to have impaired verbal memory even after a period of abstinence. Unlike alcohol, which the body clears in a matter of hours, THC is fat-soluble and can remain in body tissues for weeks.
Other studies have shown reductions in attention and concentration, verbal fluency, abstract reasoning, task accuracy and psychomotor speed.
Separately, acute intoxication with THC (i.e., “getting stoned”) has been shown to impair motor control, dual task processing, stop signal reaction times, rapid decision-making and driving ability. Marijuana use is also thought to contribute to the development of psychosis in susceptible individuals, particularly when use begins in adolescence. The long-term neurological consequences can be worse for young people because structural brain development continues well into early adulthood.
Several human and animal studies have shown that THC use in adolescents causes structural brain changes and impaired learning. A large, two-and-a-half decade study of New Zealanders showed declines in a broad spectrum of IQ measures over time, and most of the impairment was in individuals who began using during adolescence. In this group, quitting the drug did not reverse the deficits.
A common finding in these studies is that the deficits are worse the more people have used over their lifetime and the earlier they began. Marijuana use in adolescents correlates with poor academic performance, even when controlling for other factors.
In college students, it correlates with lower GPAs, lower class attendance, higher dropout rates and greater use of medical and mental health resources in later years. About 17 percent of teen users eventually become dependent on the drug.
Studies in California have shown that after legalization, adolescents are less likely to perceive marijuana as a health risk or disapprove of its use.
Also, wider access to marijuana among adults can lead to more access among youth. In a 2011 Denver study, 48.8 percent of adolescents in outpatient substance abuse treatment reported obtaining it from someone with a medical marijuana license.
According to the National Survey on Drug Use and Health, marijuana use in Colorado among people aged 12-17 increased from 10.5 percent to 12.6 percent after it was fully legalized. By the 2013-14 period, Colorado ranked No. 1 in the nation in past-month use among this group. The other state in which recreational marijuana had been legalized by then — Washington — ranked 5th.
Moreover, all states ranking in the top 20 were ones in which recreational or medical marijuana had been legalized. The 27 states without legalization were in the bottom 30.
In adults, a study of more than 39,000 Americans found the prevalence of marijuana use, abuse and dependence to have doubled between 2001 and 2013, when many states were legalizing the drug. By 2013, abuse or dependence had risen to 2.9 percent — that’s more than 6.8 million U.S. adults.
It’s true that in some patients, marijuana and marijuana-derived drugs may be therapeutically useful — for nausea, certain kinds of pain and muscle spasm, anorexia, and symptoms of PTSD — provided patients are aware of the potential harm. Alcohol has medicinal effects, too: It’s a sedative and can be used to treat alcohol withdrawal, for example.
But physicians in more economically developed nations generally don’t use alcohol therapeutically because of its side-effect profile and because there are more effective and safer drugs.
Most physicians are, understandably, against legalization. Even doctors who support it, like the members of Doctors for Cannabis Regulation, acknowledge the harmful effects of the drug and do not advocate for its use.
What these physicians argue, and what any knowledgeable proponent of cannabis legalization must argue, is that a reduction in drug-related penalties and imprisonment, a possible reduction in violent crime, open access to the limited therapeutic benefits of the drug, and an increase in personal liberty outweigh the many human costs of legalization.
But, in part, it’s a false choice. As the American Medical Association and others have pointed out, marijuana does not have to be legalized for drug laws to be changed in ways that reduce drug-related penalties and emphasize drug rehabilitation and treatment.
Reforming our drug laws while keeping marijuana illegal would send young Americans a message of compassion without signaling that the drug is safe and accepted. Moreover, it would avoid the increases in marijuana use, abuse, and dependence — and the accompanying harm — to which legalization gives rise.
R.J. Petrella is an emergency physician, researcher and author. He writes from Boston.