More states are legalizing marijuana, but concerns remain about its long-term effects on the adolescentbrain. Much of the long-term cognitive effects of cannabis have focused on heavy users. It is not clear whether there is a safe level of use. Nor is it known whether the brain changes associated with marijuana use are permanent or if the brain can recover with time.
Marijuana is the most widely used illicit drug in Canada, the United States and many other countries – but the term “illicit” may not apply much longer. Twenty-three states have legalized Cannabis Sativa for medical use since 1996. Alaska, Colorado, Oregon, Washington and Washington, D.C. now allow medicinal use of the drug for people over 21. Acceptance of marijuana is growing rapidly.
These laws are not without critics. Among the critics’ concerns is the worry that despite age limits, legalization might make marijuana more accessible to young people. An additional concern is that adolescents developing brains may be particularly vulnerable to lasting damage from the drug.
There are a lot of open questions about the long-term effects of marijuana. There are now a number of research articles all pointing in the same direction. Starting young, and using frequently may disrupt brain development.
Marijuana shows considerable promise for treating medical conditions including pain, muscle spasms, seizure disorders, sleep dysfunction and nausea from chemotherapy.
At least some of those benefits are thought to come from cannabidiol, a chemical component of the marijuana plant not thought to produce mind-altering effects. But there is still a lot to learn about marijuana and the National Institutes of Health now support more research on cannabidiol.
In the short term, marijuana has been shown to impair functions such as attention span, memory, learning and decision making. Those effects can last for days after the high has worn off.
Heavy marijuana use in adolescence or early adulthood has been associated with a dismal set of life outcomes including poor school performance, higher dropout rates, increased welfare dependence, great unemployment and lower life satisfaction.
But it is not clear that marijuana deserves the bulk of the blame. Some researchers have suggested that factors such as peer influence, emotional distress or a tendency toward problem behaviour could predispose people to drug use as well as poor life outcomes.
Few longitudinal studies have been conducted to follow the trajectories of young people before and after they take their first hit of marijuana. But one long-term study from New Zealand showed worrisome findings. One thousand New Zealanders born in 1972 answered questions about marijuana use at ages 18, 21, 26, 32 and 38. They are underwent neuropsychological testing at ages 13 and 28.
The team found that persistent marijuana use was linked to a decline in I.Q. even after the researchers controlled for educational differences. The most chronic users experienced a drop in neuropsychological functioning equivalent to about six I.Q. points. One of the researchers said “that is in the same realm as you would see with lead poisoning”.
There are some reasons to think that adolescents may be uniquely susceptible to lasting damage from marijuana use. The teenage brain doesn’t get fully myelinated – or “hard wired” until the early or mid-twenties. That is “the brain is still under construction” until then.
Another concern is that marijuana is becoming much stronger. Thirty years ago, THC concentrations were well below 10 perfect and even below 5 percent. But a recent analysis of marijuana samples sold in Colorado found THC potency reaching 30 perfect according to the results presented at the 2015 meeting of the American Chemical Society.
Despite these questions, nearly half of U.S. states have already legalized marijuana in some form and more are likely to follow suit.
In one study, data was collected on more than 11 million high school students between 1991 and 2011. Marijuana use was common among the students – about one in five reported having smoked marijuana in the past month. But in the states that legalized marijuana, the researchers found no increases in teen use following passage of the new laws.
Apparently, parents are not talking to their kids about marijuana often but retailers seem to be. In Colorado, there are marijuana ads in the free magazines that are clearly marketed to young people.
Unfortunately, marijuana producers have strong incentives to hook young users. While about 9 percent of adults who use cannabis become addicted, the rate is 17 percent for people who started smoking in their teens. And as the alcohol and tobacco industries have demonstrated, such companies make the majority of their profits in a relatively small proportion of chronic users.
There are also concerns that marijuana policy is outpacing science. The take home message is that there is a lot that is known about marijuana but a lot more that is not known.
Dr. Lee Pulos Ph.D. ABPP
Jacobus, J and Tapert, S.F. (2014). Effects of Cannabis and the Adolescent Brain. Current Pharmacological Design, 20, 2186-2193