Abnormal Psychology

Schizophrenia and Other Psychotic Disorders 535

nicotine dependence is that the cigarette use is a form of self-medication, because the

nicotine affects certain receptors in the brain related to symptoms of schizophrenia

(Kumari & Postma, 2005).

In addition, some people with schizophrenia may use alcohol and other drugs

to alleviate their symptoms:

The voices are like people having a conversation inside my head of which I am

not a part. They can be like scratching, whispers, or real loud, like shouting. They

clutter my mind and I cannot think straight until I am unable to do anything....

When I fi rst heard the voices, I would drink until I passed out. When I woke up

with a vicious hangover, the voices would be there like thunder, and I would start

drinking again.

(Hummingbird, 1999, pp. 863–864)

As is clear from this patient’s description, drinking brought temporary relief from

intrusive and persistent auditory hallucinations.

Researchers have also noted that even before their posi-

tive symptoms emerged, some people with schizophrenia abused

drugs, particularly nicotine (cigarettes), marijuana, amphetamines,

phencyclidine (PCP), mescaline, and lysergic acid diethylamide (LSD)

(Bowers et al., 2001; Weiser et al., 2004). For example, a study of

Swedish males found that those who used marijuana in adoles-

cence were more likely later to develop schizophrenia. The more

a person used marijuana, the more likely he or she was to develop

schizophrenia, particularly if the drug was used more than 50 times

(Moore et al., 2007; Zammit et al., 2002). Similarly, a longitudinal

study found that girls who used marijuana by age 18 and then later

developed schizophrenia had more symptoms of schizophrenia at

age 26 than did controls; other studies have found similar results

(Arseneault et al., 2002; Verdoux et al., 2003).

Without question, frequent use of marijuana is associated with

subsequent schizophrenia; moreover, people with schizophrenia

who also use marijuana are more likely to have aggravated symp-

toms and more relapses (Johns, 2001). However, keep in mind the

correlation between using marijuana and subsequent schizophrenia

does not show that the drug causes schizophrenia. Perhaps mari-

juana use leads to schizophrenic symptoms only in those who were

likely to develop the disorder anyway, or some aspect of a predisposition to develop

schizophrenia also might make drug use attractive. It is also possible that marijuana

“tips the scales” in those who are vulnerable but who would not develop schizo-

phrenia if they did not use the drug. Or, perhaps some other factor affects both

substance abuse and subsequent schizophrenia (Bowers et al., 2001). Researchers

do not yet know enough to be able to choose among these possibilities, and true

experiments designed to investigate them would obviously be unethical.

One study may be able to shed some light on the relationship between using

marijuana and later developing schizophrenia: The study compared marijuana use

by those who have a “predisposition” toward psychosis (e.g., a pattern of odd or

paranoid thoughts) versus those who do not have such a predisposition (Henquet

et al., 2005). The researchers began the study before any of the participants

had developed the disorder, and thus they were able to examine marijuana use prior

to emergence of the symptoms. The study not only found that marijuana use was

associated with later development of psychosis, but also that it had a greater

effect on those who were predisposed to develop schizophrenia. Moreover, the more

extensively marijuana was used, the more likely psychosis was to develop. Finally,

this study did not support the notion that those who are predisposed to develop

schizophrenia use marijuana in an attempt to medicate themselves: Those who were

predisposed were not more likely to use marijuana 4 years later.

Why might people with, or at risk for, schizophrenia be drawn to use marijuana

at all? Glimmers of an answer come from a neuropsychological study of people

with schizophrenia who used marijuana with varying frequencies. Those who used

Guitarist Peter Green (lying down), cofounder of

the rock group Fleetwood Mac, developed schizo-

phrenia after using LSD frequently. Although

Green attributes his illness to his drug abuse,

researchers cannot yet defi nitively state that such

abuse causes schizophrenia in people who might

not otherwise develop the disorder.

Araldo Di Crollalanza/Rex Features, Courtesy Everett Collection