Cannabis and its Effects in Relation to Schizophrenia

The debate continues in the United States as to whether cannabis should be legalized throughout the country. Many avid cannabis smokers advocate for cannabis legalization because it can provide some benefits to people’s health. However, studies show that cannabis can worsen psychotic symptoms especially in patients with schizophrenia.

For example, a study published in the European Archives of Psychiatry and Clinical Neuroscience consisted of a total of 39 schizophrenic patients with histories of cannabis abuse, and compared them to a control group of 39 schizophrenic patients with no history of substance abuse. At the end of the 5-year span of the study, only 27 cases and 26 controls were left to investigate. The study found that “8/27 cases (30%) had continued cannabis abuse, 6/27 (22%) had become alcohol abusers. Only one patient of the control group had started abusing alcohol. Patients with previous cannabis abuse had significantly more rehospitalizations, tended to worse psychosocial functioning, and scored significantly higher on the psychopathological syndromes “thought disturbance” (BPRS) and “hostility” (AMDP)” (Caspari et al., 1999).

Furthermore, a study published in the Biological Psychiatry journal was conducted that tested the effects of 0 mg, 2.5 mg, and 5 mg of intravenous Δ-9-tetrahydrocannabinol (Δ-9-THC) on 13 stable schizophrenic patients and compared them to the effects on healthy subjects without schizophrenia. The study found that “Delta-9-tetrahydrocannabinol transiently increased 1) learning and recall deficits; 2) positive, negative, and general schizophrenia symptoms; 3) perceptual alterations… [and] Schizophrenia patients were more vulnerable to Δ-9-THC effects on recall relative to control subjects” (D’Souza et al., 2005).

Lastly, a study published in the Arch Gen Psychiatry journal tested schizophrenic patients who abused and compared them to a group of schizophrenic patients who did not abuse cannabis. As seen in the figure below, cannabis abusers were much more likely to experience a psychotic relapse than were non-abusers (Linszen et al., 1994).

Positive and Negative Schizophrenic Symptom Severity in Relation to amount of THC over Time

Therefore, it is clear that cannabis use can be very dangerous for schizophrenic patients and can worsen addictive and psychotic behavior.

Cannabis can also have adverse psychotic effects on people without schizophrenia. For example, study published in The Lancet found that after collecting data from 35 studies, “There was an increased risk of any psychotic outcome in individuals who had ever used cannabis (pooled adjusted odds ratio=1·41, 95% CI 1·20–1·65). Findings were consistent with a dose-response effect, with greater risk in people who used cannabis most frequently (2·09, 1·54–2·84)” (Moore et al., 2007). Furthermore, a study published in the Neuropsychopharmacology journal found that administering THC on heathy subjects produced positive and negative schizophrenia symptoms. As seen in the figure below, the severity of symptoms increased with increase amounts of THC (D’Souza et al., 2004).

Percentage of Prior Schizophrenic Patients without Relapse over Time, Cannabis Abusers vs. Non-Abusers

Therefore, cannabis has the ability to cause psychotic and schizophrenic symptoms even in healthy patients.

The debate over legalization of cannabis is definitely not black and white. Many advocates praise it for its calming and healing properties. However, many research studies have adequately shown that cannabis can exacerbate psychotic symptoms and behaviors in people with schizophrenia and without it.

Works Cited

Caspari D. Cannabis and schizophrenia: results of a follow-up study. European Archives of Psychiatry and Clinical Neuroscience. Vol 249, p 45-49. 1999.

D’Souza DC, Abi-Saab WM, Madonick S, et al. Delta-9-tetrahydrocannabinol effects in schizophrenia: Implications for cognition, psychosis, and addiction. Biological Psychiatry. Vol 57, p 594-608. 2005.

D’Souza DC, Perry E, MacDougall L, et al. The Psychotomimetic Effects of Intravenous Delta-9-Tetrahydrocannabinol in Healthy Individuals: Implications for Psychosis. Neuropsychopharmacology. Vol 29, p 1558-1572. 2004.

Linszen DH, Dingemans PM, Lenior ME. Cannabis Abuse and the Course of Recent-Onset Schizophrenic Disorders. Arch Gen Psychiatry. Vol 51, p 273-279. 1994.

Moore THM, Zammit S, Lingford-Hughes A, et al. Cannabis use and risk of psychotic or affective mental health outcomes: a systematic review. The Lancet. Vol 370, p 319-328. 2007.