Background: Cannabis is the most widely used illicit drug in the world and there is
growing concern about the mental health effects of cannabis use. These concerns are at least partly
due to the strong increase in recreational and medical cannabis use and the rise in
tetrahydrocannabinol (THC) levels. Cannabis is widely used to self-medicate by older people and
people with brain disorders such as amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS),
Alzheimer’s disease (AD), Parkinson’s disease (PD), bipolar disorder, and schizophrenia.
Objective: This review provides an overview of the perceived benefits and adverse mental health
effects of cannabis use in people with ALS, MS, AD, PD, bipolar disorder, and schizophrenia.
Results: The reviewed studies indicate that cannabis use diminishes some symptoms associated with
these disorders. Cannabis use decreases pain and spasticity in people with MS, decreases tremor,
rigidity, and pain in people with PD, and improves the quality of life of ALS patients by improving
appetite, and decreasing pain and spasticity. Cannabis use is more common among people with
schizophrenia than healthy controls. Cannabis use is a risk factor for schizophrenia which increases
positive symptoms in schizophrenia patients and diminishes negative symptoms. Cannabis use
worsens bipolar disorder and there is no evidence that bipolar patients derive any benefit from
cannabis. In late stage Alzheimer’s patients, cannabis products may improve food intake, sleep
quality, and diminish agitation.
Conclusion: Cannabis use diminishes some of the adverse effects of neurological and psychiatric
disorders. However, chronic cannabis use may lead to cognitive impairments and dependence.