Public in a Haze About Marijuana's Safety

Although marijuana is increasingly viewed as a relatively safe recreational drug that even may have some medicinal benefits, a new review of more than 120 studies underscores that the drug is not as harmless as perceived — particularly for adolescents.

In an analysis focusing on various aspects of cannabis use and the adolescent brain, researchers underscore that only about 1 in 4 adolescents exposed to cannabis go on to experience adverse outcomes, but they stress the importance of identifying those who are most vulnerable, according to coauthor Didier Jutras-Aswad, MD, a psychiatrist with the University of Montreal, in Quebec, Canada.

"What the data are showing is for the majority of the population, cannabis is not associated with severe, long-term adverse outcomes, but there is a misconception that this means it is safe for nearly everyone, which is not true," he told Medscape Medical News.

"In fact, for some people, including some adolescents and even adults, as well as those with mental health problems, cannabis can have devastating effects on brain development and is associated with clear adverse outcomes, such as addiction to other substances and mental health problems."

The study was published online August 16 in Neuropharmacology.

Identifying Vulnerable Populations

Clinical and epidemiologic studies show time and again that there is a link between repeated early cannabis exposure and an increased risk for abuse of heavier drugs. However, the authors note that an important caveat is that a true causal relationship may not be clear due to the influence of genetic and environmental factors.

They do note, however, that animal studies show enhanced intake of and sensitivity to opiate drugs later in life after repeated exposure to cannabis in adolescence.

The genetic factors that increase the risk for adverse outcomes also still need to be better defined, Dr. Jutras-Aswad said.

"The evidence shows there are some genes that increase the vulnerability to cannabis and other drugs, but more needs to be known, and even if they become more clear, there are of course problems with genetic screening, ranging from ethical issues to cost," Dr. Jutras-Aswad said.

Easier to identify are personality types shown to be more vulnerable to the worst effects of cannabis, he added.

"There are other factors that can predict whether someone will experience problems, including psychological factors and types of personalities, and in the short term, that is probably the way to go — to use screening and identify those at risk — and the good thing is we already have some interventions that can help."

Interventions shown to be effective in reducing abuse include psychotherapy to target aggressive or impulsive behaviors and teaching coping with stress or becoming more effective in social relationships.

Among the challenges in making the case to the public that cannabis can indeed be harmful to some adolescents is convincing parents — many of whom emerged from the 1960s, '70s, and '80s without having experienced any noticeable long-term effects from heavy pot use.

Not Your Parents' Pot

But Dr. Jutras-Aswad notes that the cannabis available to the current generation of adolescents is a much more potent variety, with higher levels of tetrahydrocannabinol (THC), the psychoactive component in cannabis.

"It is quite clear the cannabis used in the '60s and '70s is very different from what is found on the street for the past 10 or 15 years," he said.

"The THC level in the '60s and '70s was typically under 5%, whereas for the past 10 years, we see levels of 15% to 20%, so clearly the drug is more potent, and that can certainly be associated with worse outcomes, including mental health and brain development issues."

Dr. Jutras-Aswad acknowledges that public opinion is becoming increasingly dismissive of warnings about cannabis, and he underscores that clarifying the exact nature of the risk to certain individuals is critical in getting out the right message.

"The aim of our article isn't about saying whether cannabis is good or bad," he said.

"It may indeed have medicinal value, but it can also be bad for certain very vulnerable populations, so the point is we have to be very careful about the message we send."

"We don't want to say this is the worst thing on earth or that cannabis is as bad as heroin, because clearly it's not. But at the same time, we have to make sure it's not presented as a drug that is completely harmless."

The message of focusing on those most at risk for adverse outcomes appears to be echoed in a shift of marijuana enforcement policies recently announced by the US Department of Justice (DOJ).

Although the DOJ says it will not challenge state laws that legalize marijuana, federal prosecutors are instead required to focus on 8 priorities — with preventing marijuana distribution to minors at the very top of the list.

According to the DOJ memo on the action, the priority would call for enforcement "not just when an individual or entity sells or transfers marijuana to a minor, but also when marijuana trafficking takes place near an area associated with minors; when marijuana or marijuana-infused products are marketed in a manner to appeal to minors; or when marijuana is being diverted, directly or indirectly, and purposefully or otherwise, to minors."

Other enforcement priorities include stopping drug trafficking by gangs and cartels, preventing drugged driving, and prohibiting the use of public lands for growing marijuana.

Reduced Functioning

Sharon Levy, MD, MPH, director of the Adolescent Substance Abuse Program at Children's Hospital Boston and an assistant professor of pediatrics at Harvard Medical School, agrees that as acceptance of marijuana in society increases, clearer distinctions need to be made regarding what the risks are and who is most at risk.

"At the moment, there is a lot of misinformation about marijuana flying around, including that marijuana is not addictive — it is; that smoking marijuana improves lung function — smoking anything is damaging to the lungs; and that it can even cure cancer — no comment," she told Medscape Medical News.

"I think the misinformation has been really hard for us to counter, [but] one of the greatest tools we have in getting kids to stop using is simply medical advice."

Although some research has shown troubling associations between marijuana use and psychotic disorders such as schizophrenia, Dr. Levy said the cases are rare, and the greater risk to adolescents is a more general reduced level of function.

"In terms of odds, I would say the biggest risk to teen marijuana users are poor functioning and underachievement, which can persist lifelong," she said.

"A 'motivational syndrome' has been well described, and we know that teens that use marijuana have poorer life outcomes than their peers in terms of educational, job, and family achievement. However, this is a very slow process that is difficult to identify."

"But the truth is that we know marijuana is not completely benign," she added.

"That doesn't necessarily mean it needs to be illegal, but if we are putting legalization up for popular vote, then the population should be well informed both on what we do know as well as the limits to our knowledge."

The study received funding from National Institute on Drug Abuse grants DA030359 and DA023214. The authors and Dr. Levy have disclosed no relevant financial relationships.

Neuropharmacology. Published online August 16, 2013. Abstract

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