Q: Due to increasing social acceptance, I find it is becoming harder to convince my adolescent patients that there are risks to using marijuana. Are there any strategies that you find useful?
A: I try to help my adolescent patients understand that using marijuana during adolescence entails health risks that adult marijuana users do not seem to have. One of the most concerning adolescent risks is developing hallucinations and psychosis from the use of marijuana. If this psychosis risk was limited to only a few days reaction after last cannabis use it would be far less frightening, but this instead can involve the development of longer-term psychosis, or schizophrenia.
Evidence of the marijuana psychosis risk in adolescence has come from many different areas of epidemiologic study. For instance, cohort studies looking at the past substance use history of adults with significant psychosis found they had at least twice as much marijuana use before developing their symptoms than their age- and region-matched peers — an association not as clearly found for other drugs of abuse.1,2 The risk of developing long-term psychosis has also been found to increase proportionally with increasing frequency of marijuana use in a dose-response fashion, a finding that on its own would suggest causality.3 Investigations following adolescent marijuana abusers frequency of developing adult mental health disorders have found that the association with non-psychotic adult mental health syndromes like the mood disorders is weak. Thus, the future mental health disorder risk for marijuana abusers appears to be relatively specific to psychosis. Multiple analyses have further found that cannabis users who developed schizophrenia had a significantly earlier age of onset of symptoms than non-users, which is important because a younger age of onset is a very strong predictor of poor future prognosis among schizophrenia patients.1
It should be noted that even though the above significant associations were all controlled for covariates in their research designs, associations cannot on their own be a proof of causation. Theoretically, adolescents with pre-psychotic symptoms like social withdrawal could for some other undefined reason be preferring to recreate by using marijuana over any other drugs of abuse just before developing their overt psychosis. However, I would add that having witnessed adolescents with high pre-morbid functioning develop long-term psychosis without any signs of having such risks before abusing marijuana, the “it is just a coincidence” explanation, to me, is unsatisfactory. Because the association between adolescent marijuana abuse and future development of psychosis has become quite accepted in the literature, a current direction of research is to work out the neurologic mechanisms for how the damage is occurring.
Neuroscience research has shown that the adolescent brain is not the same as the adult brain, in terms of information processing pathways, numbers of neurons, their degree of dendritic connections, and their degree of myelination. Anything that disrupts normal brain development, connection, and pruning processes in adolescence can understandably have lasting effects. One of the current theories is that stimulating the cannabinoid receptor alters glutamate and gamma-aminobutyric acid (GABA) functioning, and the altered glutamate and GABA functioning is what leads to neurostructural changes unique to the adolescent brain.4
Therefore, I now educate my adolescent patients that they have an age-related risk of developing long-term hallucinations or schizophrenia from abusing marijuana, which tends to get their attention. Thankfully, most adolescents who abuse marijuana do not become psychotic adults.
- Tosato S, Lasalvia A, Bonetto C, et al. The impact of cannabis use on age of onset and clinical characteristics in first episode psychotic patients. J Psychiatr Res. 2013;47(4):438–444. doi:10.1016/j.jpsychires.2012.11.009 [CrossRef]
- Mazzoncini R, Donoghue K, Hart J, et al. Illicit substance use and its correlates in first episode psychosis. Acta Psychiatr Scand. 2010;121(5):351–358. doi:10.1111/j.1600-0447.2009.01483.x [CrossRef]
- Henguet C, Krabbendam L, Spauwen J, et al. Prospective cohort study of cannabis use, predisposition for psychosis, and psychotic symptoms in young people. BMJ. 2005;330(7481):11. doi:10.1136/bmj.38267.664086.63 [CrossRef]
- Bossong MG, Niesink RJM. Adolescent brain maturation, the endogenous cannabinoid system and the neurobiology of cannabis-induced schizophrenia. Prog Neurobiol. 2010;92(3):370–385. doi:10.1016/j.pneurobio.2010.06.010 [CrossRef]