Your Teen's Brain on Weed: Is it safe?


“Mom…really. I don't smoke that much. It actually improves my creativity. You and dad are really crazy. I'm not doing anything to hurt myself. I'm earning all As so what's the problem?”

“John and I smoked in the 70's and 80's. We don't think there is anything wrong with it. Can it really be that bad for our son?”

Ever since Colorado legalized recreational cannabis use ten months ago, parents have been asking me if it is really safe for their teen. They remember weekends of smoking during college and think that it is harmless. On the other hand, teenagers to young adults have assumed that such use is normal and perfectly o.k. However, recent research suggests otherwise.

Marijuana is the most widely used illicit drug in the United States.

Marijuana is the most widely used illicit drug in the United States. It is estimated that 69 percent of 12 th graders have tried alcohol, 45 percent have tried marijuana, and 23 percent have used it in the past month. Seven percent of these students have used it daily.

Robert Booth, Ph.D., of the University of Colorado School of Medicine, presented his findings on the costs of marijuana use during a congressional briefing last June. He found that the number of students expelled or suspended for drugs in Colorado schools each year increased from approximately 4,000 to more than 5,279 during the 2011-12 school year since Colorado began to implement its medical marijuana laws in 2009 (Miller, 2014). Dr. Booth also said that arrests due to driving under the influence of marijuana tripled from 2009 to 2012.

Attention, memory, and learning. Have you every wondered if marijuana use affects your teen's thinking?

Researchers are also approaching this from a scientific perspective. We now know that teens smoking marijuana are especially vulnerable to problems with thinking because of the maturing of their brain compared to adults.

“Under age 21, the brain is developing rapidly and is particularly vulnerable. A large-scale study by Madeline Meier Ph.D. and colleagues (2012) found an average eight-point IQ decline and persistent attention and memory problems in midlife in those who started using in their teens. The researchers concluded that marijuana had a toxic effect on the developing brain ,” said Patricia Gross, Ph.D. Assistant Clinical Professor at the UCLA Department of Psychiatry and Biobehavioral Sciences.

Dr. Gross also said, “ More ominous is the fact that marijuana use in teens contributes to an increased risk of psychosis in later life (Radhakrishnan et al., 2012; Sewell et al., 2010). The younger the user, the greater the risk. Smoking marijuana as few as five times under the age of 15 substantially increases the risk of later psychotic symptoms (Andreasson et al., 1987).”

Teens and young adults (16-25) who use marijuana suffer from cognitive and psychological effects up to one month after abstinence.

Some researchers have indicated that adolescents suffer from thinking and psychological effects even up to one month after discontinuing marijuana (Medina et al., 2007). Problems with verbal learning, processing speed, mood, attention, and planning and organizational skills have been areas of concern (Winward et al., 2014). These findings implicate the sensitivity of adolescent brains to marijuana, which suggests the real possibility of marked changes cognitively and psychologically (Squeglia et al., 2014; Crane et al., 2013; Lisdahl & Price, 2012).

As a psychologist who specializes in pediatric/young adult neuropsychological assessment, I regard the current research findings as a wake-up call so that our children can be better informed about the consequences of marijuana use and even the concurrent use of alcohol. As Dr. Gross concludes, “ Parents of teens take warning: this is not your marijuana. The cannabis smoked by children today is about 15 times more powerful than what you used years ago, according to the British Lung Association.”

I think we can all agree that everyone including parents, educators, and health professionals need to pay close attention to the research. Teens need to be informed.

Karen L. Schiltz, Ph.D. is a Clinical Professor (Voluntary) at the UCLA Medical Psychology Assessment Center. She is co-author of, Beyond the label: A guide to unlocking a child's educational potential (Oxford University Press, 2012). Her practice specializes in pediatric/young adult clinical neuropsychology in Calabasas, California.

Patricia Gross, Ph.D. is a board-certified clinical neuropsychologist with 30 years of experience.  She holds a doctoral degree in Clinical Psychology from the University of Southern California and completed a postdoctoral fellowship in Clinical Neuropsychology from the Neuropsychiatric Institute, now the Semel Institute, at UCLA.  Dr. Gross was recently appointed Assistant Clinical Professor (Voluntary) at the David Geffen School of Medicine at UCLA.


Andreasson, S., Allebeck, P., Engstrom, A., & Rydberg, U. (1987). Cannabis and schizophrenia. A longitudinal study of Swedish conscripts. Lancet, 2, (8574): 1483-1486.

Crane, N. A., Schuster, R. M., Fusar-Poll, P., & Gonzalez. (2013). Effects of cannabis on neurocognitive functioning: Recent advances, neurodevelopmental influences, and sex differences. Neuropsychology Review , 23: 117-137.

Lisdahl, K. M. & Price, J. S. (2012). Increased marijuana use and gender predict poorer cognitive functioning in adolescents and emerging adults. Journal of the International Neuropsychology Society , 18: 678-688.

Medina, K. L., Hanson, K. L., Schweinsburg, A.D., Cohen-Zion, M., Nagel, B. J., & Tapert, S.F. (2007). Neuropsychological functioning in adolescent marijuana users: Subtle deficits detectable after a month of abstinence. Journal of the International Society , 13: 807-820.

Meier, M.H., Caspi, A., Ambler, A., Harrington, H., Houts, R., Keefe, R.S.E., McDonald, K., Ward, A., Poulton, R., & Moffitt, T. E. (2012). Persistent cannabis users show neuropsychological decline from childhood to midlife. Proceedings of the National Academy of Sciences , doi: 10.1073 Miller, A. (2014). Are marijuana legalization laws based on bad science? Monitor on Psychology, 45: 11.

Radhakrishnan, M., Addy, P.H., Sewell, R.A., Skosnik, P.D., Ranganthan, M., & D'Souza, D.C. (2012). Cannabis, cannabinoids, and the association with psychosis. In: Madras, B., & Kuhar, M.J. (Eds.) The effects of drug abuse on the human nervous system. Neuroscience-Net, LLC.

Sewell, R.A., Skosnik, P.D., Garcia-Sosa, I., Radhakrishnan, M., & D'Souza, D.C. (2010). Behavioral, cognitive, and psychophysiological effects of cannabinoids: relevance to psychosis and schizophrenia. Revista Brasileira de Psiquiatria , 32(1), S15-S30.

Squeglia, L. M., Jacobus, J., Nguyen-Louie, T. T., & Tapert, S. F. (2014). Inhibition during early adolescence predicts alcohol and marijuana use by late adolescence. Neuropsychology . 28: 782-790.

Winward, J. L., Hanson, K. L., Tapert, S. F., & Brown, S. A. (2014). Heavy alcohol use, marijuana use, and concomitant use by adolescents are associated with unique and shared cognitive decrements. Journal of the International Neuropsychological Society , 20: 784-795.

Best Always,
Karen L. Schiltz Ph.D.


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