by Ken Duckworth, M.D.
NAMI Medical Director
The ongoing link between use of marijuana in teens and the increased risk of developing schizophrenia has been further developed in a recent Dutch study published in the British Medical Journal (BMJ) and has re-ignited that area of interest. This study has important public health implications, because our capacity to prevent psychiatric illnesses is severely limited-although a recent small Omega-3 fatty acid study in the Archives of General Psychiatry suggests, in contrast, a protective impact.
The BMJ study looked at young adults who were at risk for psychosis and found that the rate of conversion to the illness was 51 percent with marijuana users-compared with 26 percent of nonusers. This study builds upon a growing body of literature that is making this causative link. This build upon other studies-one of the most interesting to me was a study that made a case for delaying all experimentation---the study found that users before age 15 were 4.5 times more likely to develop schizophrenia than nonsmokers, and those who delayed until age 18 had a risk of 1.6. This strongly suggests that, in addition to abstinence, delaying experimentation results in reduced risk.
Why do some people have no issues with this choice while another subset will never be the same after use? We do not know for sure, but interest has been growing on looking at generic variability. A gene variation in the metabolism of the neurochemicals dopamine may confer much of the risk. Unfortunately, there is not a test to determine if a group of teens will become symptomatic if they experiment. So all teens have an unknown but variable risk-a difficult area to impart wisdom in. It is very hard to be sure what the risk for use of marijuana is for any one teen, but use is clearly risky when you look at a population as a whole. This risk is even worse for kids with a family history of psychosis.
As a father of three teen girls (who also has a history of bipolar disorder with psychosis in my genes), I do my best to share with my kids that, in my view, all drug experiments need to be delayed-or denied. Teens are notorious for not listening to parents and for not delaying gratification, so I can't know what is actually getting through. I suspect it is less than I would like. Developing good decision-making skills is one of the key aspects of growing up, but there is no one way to get there. Learning by experimentation is one way, but as these studies show, the consequences can be much greater than anticipated.
Knowing your family risk (e.g. of schizophrenia or alcoholism or diabetes) is a good perspective to share with your kids so that they know that drugs, alcohol and sugar are even more worrisome for them. What they do with that kind of information is beyond parental control. Like teaching teens to drive a car, you hope to model and impart experience, and then you wait as they learn. I encourage my kids and the people who live with mental illness whom I treat as a doctor to wear seat belts and to avoid drugs. Then like all parents, I hope for the best and do my best to coach as more data comes in on their choices. But there are no guarantees. In neurobiology--just like with driving vehicles--all we can do is work to lower the chance of complications.