The connection between cannabis use and psychiatric disorders, particularly schizophrenia, is supported by a large body of research, but the debate continues as to whether one has a more causative effect than the other.
A common argument against marijuana legalization, for example, is that the drug is associated with increased psychosis risk. Though causation has not been established, these criticisms imply that cannabis use results in psychosis. It is unclear whether that is the case or if people with psychotic disorders are engaging in a form of self-medication.
Indeed, cannabis impacts the very system that research suggests has a major role in schizophrenia, the endocannabinoid system, which is involved in neurotransmission and helps to regulate functions such as sleep, cognition, emotion. The endocannabinoid system is also involved in reward processing, which recent findings suggest is deficient in patients with schizophrenia spectrum disorders.1,2
The primary psychoactive component of cannabis, Δ9-tetrahydrocannabinol (THC), exerts its effects by binding to cannabinoid receptors in the endocannabinoid system, explained Matthijs Bossong, PhD, of the Rudolf Magnus Institute of Neuroscience at the University Medical Center Utrecht in the Netherlands. THC is one of approximately 80 different cannabinoid compounds present in cannabis, the vast majority of which do not cause intoxication.
“It has been shown that patients with schizophrenia have enhanced levels of endogenous cannabinoids as measured both in their blood and cerebrospinal fluid,” and neuroimaging studies and post-mortem examinations have shown that they have increased levels of cannabinoid receptors in their brains, Bossong told Psychiatry Advisor.
A review that he co-authored while he was at the Institute of Psychiatry at King’s College London provides further support for the involvement of the endocannabinoid system in symptoms of schizophrenia.3 “For many brain functions, such as memory, executive function and emotional processing, we found striking similarities between cannabis-intoxicated healthy volunteers” and non-intoxicated schizophrenia patients,” Bossong added.
On the behavioral level, it is clear that people with schizophrenia have elevated rates of cannabis use. A small collaborative study published in September in Schizophrenia Research, by researchers at the Geisel School of Medicine at Dartmouth College and the Massachusetts Institute of Technology, states that up to 42% of patients with schizophrenia have comorbid cannabis-use disorder, which significantly worsens the progression of the disease.2