Marijuana Use Is a Symptom, Not a Cause, of Mental Illness

Heavy marijuana users do badly at work or school, and are more likely to be delinquent and develop psychiatric problems, or have abnormal brain waves. Time and again, however, such studies encounter the same objection: are the problems caused by smoking marijuana, or is it just that people with problems are more likely to end up using marijuana heavily? It turns out that, in the case of delinquency, schizophrenia and mental illnesses, the balance of the evidence points to the second explanation. Marijuana doesn't cause the problems, although it may make them worse. Some schizophrenics, for example, are drawn to the drug because it eases their sense of social alienation. And most researchers now accept that the evidence linking marijuana to abnormal brain waves vanishes when people with psychiatric problems, illnesses or a history of general drug abuse are excluded from studies.