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The Dangers of Marijuana in Adolescence

Act now to reduce long-term damage from your teen’s heavy cannabis use.

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I recently heard from a father who had just discovered that his 15-year-old daughter was using cannabis heavily. He told me that she’d done some self-cutting when she was younger, for which she (and the whole family) had seen a therapist. He asked me how he should respond to this latest problem. Was cannabis as innocuous as so many now claim it to be?

The short answer is: “Yes, and no.” In many ways, research findings are showing that cannabis use is less problematic for adults than an equivalent reliance on cigarettes or alcohol. When it comes to adolescents, however, cannabis use is seriously dangerous. There are very good reasons that no North American jurisdiction that has legalized cannabis allows it to be sold to or used by people under 21.

A recent book describes the results of three linked longitudinal studies that investigate physical, psychological, and behavioral influences on human development from 3 months to 38 years of age. One of the factors the authors consider is the impact of cannabis use on health, cognition, success, and relationships.

In The Origins of You: How Childhood Shapes Later Life, Jay Belsky, Avshalom Caspi, Terrie Moffitt, and Richie Poulton write that although most adults don’t have serious problems related to cannabis use, it’s different for teenagers. Those who start using cannabis heavily by age 15 are significantly more likely than others to develop schizophrenia. Persistent cannabis dependence that starts in the mid-teens is also associated with reduced intelligence quotient, cognitive problems, academic problems, downward socioeconomic mobility in adulthood, as well as financial difficulties, problems in the workplace, and conflicted intimate-partner relationships. The researchers found that the more heavily a teenager used marijuana, the greater the problems they experienced, problems persisting at least into midlife.

The authors also note that cannabis has become much more potent in the 25 years since their study participants were in their teens and that this almost certainly has implications for mental health, neuropsychological functioning, and work and family life. A 15-year-old today is likely to experience considerably more harm from the same amount of cannabis as their research participants.

Based on the findings reported here, as well as many other sources, I told the dad who had questions about his daughter that this was indeed a serious issue and required urgent action. Here are my recommendations to him, which I’m sharing here for other parents facing similar concerns:

1. Inform your child of the dangers. Many teens think cannabis is harmless. With patience, love, and no judgment, make sure your daughter knows the serious potential consequences to her brain and mental health and the long-term, real-world outcomes of heavy marijuana use at her age.

2. Get professional help ASAP. Try to find an adolescent psychiatrist or psychologist. Your daughter needs an assessment for depression, anxiety, bullying victimization, or other concerns, as well as cannabis use. (Note: This was particularly important in this case because of prior problems with self-harm.)

3. Stay connected. Spend as much time with your child as she will allow. Tell her you love her and are available in any way she needs you. When she is being impossible, difficult, or non-responsive, focus your mind and heart on the little girl she used to be. She is still that person. Find a photo of her at her sweet, curious, and most lovable best, and post it on the refrigerator, so she sees it, and you do too. Look for things to do together that she might enjoy.

4. Provide outlets for creative self-expression. Encourage and support your daughter in getting involved in creative activities—painting, sculpture, dance, writing, film, photography, whatever might interest her.

5. Keep her safe. Do what you can to separate your child from her cannabis-using friends.

6. Go away together. Once you are reassured she doesn’t need urgent professional treatment that will keep you close to home, think about going away somewhere together to get her out of the toxic environment. Rent a cottage for a few months, or visit relatives who live out of town, planning to stay a few months or longer. Even better, go somewhere she’ll encounter a new culture or language.

Yes, this is extreme, and it may sound impossible, and it may seem unfair to your other family members, but if your daughter had been given a diagnosis of serious cancer that required you to move with her for a few months to somewhere far away for treatment, you’d figure out how to make that happen. This is not less urgent than that.

7. Stay with it. Yes, this is serious. But the research also shows the power of love and connection and support, which is especially important at this vulnerable developmental stage. Your being there for your daughter now can make all the difference in the life she ends up making for herself.

This post is part of a series based on The Origins of You: How Childhood Shapes Later Life by Jay Belsky, Avshalom Caspi, Terrie E. Moffitt, and Richie Poulton. See also, in this series,


Cannabis and the Adolescent Brain,” by Helen Shen

Marijuana and Teens,” by the American Academy of Child and Adolescent Psychiatry

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