Harvard Study Shows Marijuana Does Not Cause Teen Schizophrenia

On the Internet recently, there have been many articles that connect schizophrenia and the use of marijuana. On Everyday Health, for instance, an article described a study that indicated teens with a genetic predisposition for schizophrenia and who use marijuana could face an increased risk of schizophrenic psychosis.

Furthermore, there is some evidence that point to the use of marijuana triggering schizophrenic symptoms. This was the case for a young boy who used drugs during his adolescence. Now, 40, he looks back and realizes that the drugs he used during his teens might have triggered the onset of a psychotic break, which he experienced in college. He began to hear voices, experience delusional thinking, and suffered from anxiety, depression, and mania. During college, he admitted himself into a hospital and continues to manage his mental illness even today.

Because of these connections, researchers from Harvard Medical School and VA Boston Healthcare System wanted to test the notion that marijuana can trigger a teen who is already predisposed to experiencing schizophrenia.

Schizophrenia is a mental illness that affects thinking, feeling, movement, and behavior. It is a severe psychological disorder that can significantly affect a teen’s life. Its symptoms are clinically divided into three main categories: positive, negative, and cognitive. Typically, schizophrenia shows up in late adolescence. In order for a teen to be diagnosed, the following symptoms must last longer than six months.

  • Positive Symptoms: These are those symptoms that would not normally occur without the illness, such as certain sensations, beliefs, and behaviors. Typically, they are quite noticeable by others, particularly delusional beliefs or behavior that is in response to experiencing a hallucination. Positive symptoms include disturbances in thought, delusions, hallucinations, certain erratic feelings, changes in movement, unusual behavior, and psychosis.
  • Negative Symptoms: These symptoms are the absence of certain abilities. These can include low energy, low motivation, poor social skills, little facial movements, and less than lively physical movement.
  • Cognitive Symptoms: These are symptoms that refer to difficulty with concentration and memory, such as disorganized thinking, slow thinking, difficulty understanding, poor concentration, poor memory, difficulty expressing thoughts, and having a hard time integrating thoughts with feelings and behavior.

The study found that there was little support for marijuana use triggering a psychotic episode or schizophrenia. The Harvard study compared families with a history of schizophrenia and those without. The researchers indicated “having an increased familial morbid risk for schizophrenia may be the underlying basis for schizophrenia in cannabis users and not cannabis use by itself.”

Furthermore the study examined both non-psychotic cannabis users and non-cannabis user controls as additional independent samples in order to further assess whether the risk of teen schizophrenia is increased when family members use marijuana compared to family members who do not use the drug.

The marijuana- schizophrenia connection is important to research at a time when marijuana has been legalized in some states and becoming an easy recreational drug for teens. Furthermore, it’s very common for teens with mental illness to use drugs and drink. This is especially true for those who experience the more challenging psychological illnesses such as teen schizophrenia. The National Alliance on Mental Illness (NAMI) reports that 47% of those with schizophrenia also have an addiction to alcohol or drugs. This is about four times greater than the general public.

The Harvard researchers concluded that the results of the study (and there are more forthcoming) suggest that the increased familial risk for schizophrenia is the underlying basis for the development of the psychological illness, not the use of marijuana. The research was published in Schizophrenia Research.


Grohol, J. (2013). Harvard: Marijuana Doesn’t Cause Schizophrenia. Psych Central. Retrieved on August 6, 2014, from http://psychcentral.com/news/2013/12/10/harvard-marijuana-doesnt-cause-schizophrenia/63148.html