February 8, 2016

Possible Link Between Marijuana and Psychosis

images pshycosis

Psychosis refers to an abnormal condition of the mind described as involving a “loss of contact with reality”. People with psychosis are described as psychotic. People experiencing psychosis may exhibit some personality changes and thought disorder. Depending on its severity, this may be accompanied by unusual or bizarre behavior, as well as difficulty with social interaction and impairment in carrying out daily life activities.  Source: Wikipedia

By Rheagan Rizio, USC Student and Be Well USC blogger

With several states (Oregon, Washington, Alaska and Colorado) legalizing the sale and possession of marijuana, its prevalence in the US will likely grow in the coming years. However, according to The Office of National Drug Control Policy, it is important to note that variances in state laws do not change the fact that marijuana is still considered an illegal substance on the federal government level. Additionally, there are huge differences in marijuana laws from one state to another (for example, Washington D.C. has legalized the growth and possession of marijuana but not the sale of it).

Marijuana, sometimes called cannabis, contains chemicals called cannabinoids which affect the central nervous system (CNS). They work by binding to certain sites in the brain and on nerves. According to WebMD, cannabinoids may weaken the immune system and make it harder for the body to fight off infection, and long-term use can increase lung problems; much like with tobacco, there appears to be a correlation between regular, long term use, lung cancer and emphysema. A study in 2011 has also suggested there may be a connection between marijuana use and the development of psychosis in later life, especially when used by adolescents (Kuepper et al., 2011). Another study, “Association or cannabis use during adolescence, prefrontal CB1 receptor signaling, and schizophrenia,” links the possible increase in psychosis with the fact that marijuana interferes with and distorts neurodevelopment, especially of the prefrontal cortex. The prefrontal cortex covers the front part of the frontal lobe, and has important implications in complex cognition, decision making, and social behavior (“Prefrontal cortex,” Psychology Wiki): when used to get high, marijuana inhibits many of these actions (making it difficult to think clearly and to act appropriately in certain situations), and, when used frequently before brain development is complete, can permanently alter the function of this area .

The study, “Continued cannabis use and risk of incidence and persistence of psychotic symptoms: 10 year follow-up cohort study,” followed 1923 individuals (aged 14-24 at the start of the project) over a 10-year period: the goal was to see how cannabis use in adolescence affected them throughout their lives. The researchers checked their usage three times: once at the beginning of the study, once again after 3 1/2 years, and finally after 8 1/2 years. The results were very interesting: in individuals with no symptoms of psychosis or prior cannabis use at the beginning of the study, cannabis use between first and second check-in increased psychotic symptoms for the third check-in, and continued use between the second and third check-ins increased this further. Psychotic symptoms were much higher in the experimental group than the control group (who did not use cannabis over the 10-year period), leading the researchers to conclude that cannabis use is a risk factor for psychosis.

There also appears to be a relationship between cannabis use and an earlier age of onset of symptoms (possible it speeds up the onset for at-risk individuals). In an analysis study compiled in 2011 entitled “Cannabis use and earlier onset of psychosis: a systematic meta-analysis,”researchers reviewed 443 cases that documented both the age of onset of psychotic symptoms and previous substance use, and found 83 to meet their desired criteria. According to the data, “the age at onset of psychosis for cannabis users was 2.70 years younger than for nonusers; for those with broadly defined substance use, the age at onset of psychosis was 2.00 years younger than for nonusers” (Large et al., 2011). They concluded that there is evidence that cannabis use is linked with an earlier onset of psychosis, and they supported that cannabis can cause psychosis to develop in some patients that had not displayed symptoms before.

Much more research must be completed before a definite answer on this subject can be presented. At this point, scientists have suggested there may be a correlation, but correlation is not the same as causation and therefore this is not yet accepted as fact. However, it is important to be aware of this more newly-discovered danger that marijuana poses, especially for individuals of college age.


Caballero, A. and Tseng, K. “Association of cannabis use during adolescence, prefrontal CB1 receptor signaling, and schizophrenia.” Frontiers in Pharmacology 3. 2012: 101. 2012. Electronic.
Kuepper, R., J. van Os, R. Lieb, H.U. Wittchen, M. Hofler, and C. Henquet. “Continued cannabis use and risk of incidence and persistence of psychotic symptoms: 10 year follow-up cohort study.” BMJ 342:738. 2011. Print
Large, M., S. Sharma, M.T. Compton, T. Slade, and O. Nielssen. “Cannabis use and earlier onset of psychosis: a systematic meta-analysis.” Arch Gen Psychiatry 68:6. 2011: 555-561. Print.
“Marijuana.” WebMD. Electronic.
“Marijuana Resource Center: State Laws Related to Marijuana.” The Office of National Drug Control Policy: The White House. Electronic.
“Prefrontal cortex.” Psychology Wiki. Electronic.