Around 2% of the UK population has Bipolar Disorder, with up to 60% using cannabis at some point in their lives, but research in this area is limited and reasons for high levels of use are unclear.
Dr Elizabeth Tyler of the Spectrum Centre for Mental Health Research at Lancaster University led the study, published in PLOS ONE, with Professor Steven Jones and colleagues from the University of Manchester, Professor Christine Barrowclough, Nancy Black and Lesley-Anne Carter.
She said: “One theory that is used to explain high levels of drug use is that people use cannabis to self-medicate their symptoms of bipolar disorder. “ The study looked at people diagnosed with bipolar disorder but who were not experiencing a depressive or manic episode during the six days the research was carried out.
Each participant completed a paper diary about their emotional state and drug use at several random points daily over a period of week. This enabled people to log their daily experiences in the moment before they forgot how they were feeling.
An individual with experience of bipolar disorder and cannabis use commented: “I do smoke a small amount to lift my mood and make myself slightly manic but it also lifts my mood and switches me into a different mind-set”.
“I do not use weed to manage depression as it can make it worse, making me anxious and paranoid”.
“I have found though that if I have smoked more excessively it can make me feel depressed for days afterwards”.
The study found that the odds of using cannabis increased when individuals were in a good mood. Cannabis use was also associated with an increase in positive mood, manic symptoms and paradoxically an increase in depressive symptoms, but not in the same individuals.
Dr Tyler said: “The findings suggest that cannabis is not being used to self-medicate small changes in symptoms within the context of daily life. However, cannabis use itself may be associated with both positive and negative emotional states. We need to find out whether these relationships play out in the longer term as this may have an impact on a person’s course of bipolar disorder.”