Researchers from Columbia University have found that people with depression are around twice as likely to use cannabis than those without the condition.
For the study, they analyzed data collected between 2005 and 2016 from 16,216 adults aged between 20 and 59 years old. Used to track cannabis use over time, the data was taken from the National Health and Nutrition Examination Survey, a national, annual, cross-sectional survey in the US.
In the survey, participants were asked how many times they had used cannabis in the last 30 days. They were then split into three groups: one which had not used cannabis in the last month, one which had used the substance once, and one which used the substance on a daily or near-daily basis (characterized by 20 uses in the previous month).
The researchers then assessed each participant with the Patient Health Questionaire-9, a survey that asks patients about certain mental health symptoms to identify whether they were depressed. Overall, 1,413 out of the 16,216 participants screened positive for major depression. From this group, 81% also reported their condition leading to difficulties in the work, home or relationships.
While the rate of depression remained stable among the entire cohort, the researchers noticed a sharp increase in cannabis use among individuals with the condition. Between 2005 and 2006, people with depression were 46% more likely than those without to use cannabis, and 37% more likely to use the substance on a near-daily basis. By 2015-2016 however, these figures increased to 130% and 216%, respectively.
The researchers say that the trend is concerning, especially given that both heavier cannabis use and depression are linked to an increased risk of cannabis-related harm. They further say that their results provide evidence that cannabis may not effectively treat depression, and that clinicians should communicate this with patients before prescribing the substance.