At the other end of the spectrum is the plethora of studies that have found negative associations between cannabis use and health. They are listed below.
Mental health problems
Daily cannabis use is believed to exacerbate existing symptoms of bipolar disorder among people who have this mental health problem. However, the National Academies of Sciences, Engineering, and Medicine report suggests that among people with no history of the condition, there is only limited evidence of a link between cannabis use and developing bipolar disorder.
Moderate evidence suggests that regular cannabis users are more likely to experience suicidal thoughts, and there is a small increased risk of depression among cannabis users.
Cannabis use is likely to increase risk of psychosis, including schizophrenia. But a curious finding among people with schizophrenia and other psychoses is that a history of cannabis use is linked with improved performance on tests assessing learning and memory.
Testicular cancer
Although there is no evidence to suggest any link between using cannabis and an increased risk for most cancers, the National Academies of Sciences did find some evidence to suggest an increased risk for the slow-growing seminoma subtype of testicular cancer.
Respiratory disease
Regular cannabis smoking is linked to increased risk of chronic cough, but “it is unclear” whether smoking cannabis worsens lung function or increases the risk of chronic obstructive pulmonary disease or asthma.
A
The authors of that study — published in the journal Current Opinion in Pulmonary Medicine — conclude:
“There is unequivocal evidence that habitual or regular cannabis smoking is not harmless. A caution against regular heavy cannabis usage is prudent.”
“The medicinal use of cannabis is likely not harmful to lungs in low cumulative doses,” they add, “but the dose limit needs to be defined. Recreational use is not the same as medicinal use and should be discouraged.”
There is evidence that demonstrates both the harms and health benefits of cannabis. Yet despite the emergence over the past couple of years of very comprehensive, up-to-date reviews of the scientific studies evaluating the benefits and harms of the drug, it’s clear that more research is needed to fully determine the public health implications of rising cannabis use.
