Does Substance Abuse affect Schizophrenia?
Substance abuse is a common concern of the family and friends of people with schizophrenia. Since some people who abuse drugs may show symptoms similar to those of schizophrenia, people with schizophrenia may be mistaken for people high on drugs. Sometimes families feel that street drugs can bring on schizophrenia yet most researchers do not believe that substance abuse causes schizophrenia. People who have schizophrenia often abuse alcohol and/or drugs, and may have particularly bad reactions to certain drugs. Substance abuse can reduce the effectiveness of treatment for schizophrenia. Stimulants (such as amphetamines or cocaine) may cause major problems for patients with schizophrenia, as may PCP or marijuana. In fact, some people experience a worsening of their schizophrenic symptoms when they are taking such drugs. Substance abuse also reduces the likelihood that patients will follow the treatment plans recommended by their doctors.
Cannabis
An association between cannabis use and schizophrenia was established decades ago (Andreasson, Allebeck et al. 1987). These findings have been corroborated by further research. Essentially, the conclusions drawn from many of these studies were that cannabis use causes schizophrenia. However, it is unlikely to be so simple. Undoubtedly, these studies are extremely important, although they are far from conclusive.
There may be a number of reasons that could account for the association between schizophrenia and cannabis. For example, it is possible that cannabis use may cause schizophrenia in vulnerable individuals (ie. a risk factor – as smoking cigarettes are to heart disease). On the other hand, it may be that people with schizophrenia are inherently more likely to abuse cannabis, either in an attempt to self medicate or because there is a more general link with substance abuse. Indeed, people with schizophrenia are much more likely to abuse any drug and it is thought that around 50% of people with schizophrenia are substance abusers. Also, mental illness in general is associated with greater rates of substance abuse.
Another interesting study found that mental illness at age 15 was associated with cannabis use at age 18. Conversely, cannabis use at age 18 was associated with mental illness at 21 years. This suggests that in adolescence mental illness causes substance use, but that in adulthood, this association may be reversed.
Interestingly, even though rates of cannabis use have significantly increased in recent decades, rates of schizophrenia do not appear to have changed appreciably over this same period.
