Cannabis link to depression, suicide
A member of the Medical Cannabis Research Collaboration has urged consideration of a British review investigating the link between cannabis use during adolescence and the risk of developing major depression and suicidal behaviour.
Associate Professor Giles Newton-Howes, from Otago University’s Department of Psychological Medicine, said while individual risk was moderate to low, the high prevalence of young people consuming cannabis meant there was potential for large numbers of young people to be affected.
“This is an important and interesting review of the literature examining the association between teenage use of cannabis and later depression and anxiety,” he said.
“It is a high-quality study, with careful and systematic collection of data, a sensible strategy to examine the data and well-considered comments on research that is related but could not be statistically analysed.
“It is important to New Zealanders, as we are considering increasing the number of people who can smoke cannabis for medical reasons — a change that seems to have increased adolescent use overseas — and are going to consider the topic as a nation next year. It is also important as it includes New Zealanders in the people studied, and the other people are from similar social backgrounds, so this study relates to us.”
The researchers had found a clear “and quite big” association between teenage cannabis use and adult depression, but not anxiety.
“This association is also found for suicidal thinking and attempts, and is also quite big, however there are fewer studied in this part of the analysis,” Professor Newton-Howes said.
“Although this review and analysis does not prove causality, it is further evidence that cannabis has the potential to harm the developing teenage brain, and we ignore these risks at our peril as a nation as we grapple with the cannabis debate.”
Professor Celso Arango, President of the European College of Neuropsychopharmacology, said the relationship between cannabis and psychosis (cannabis-caused psychosis; use of cannabis decreased age at onset in cases of the first psychotic episode; for people with psychotic disorders cannabis use increased the risk of relapse and worsened the prognosis) had long been known.
“In this case the metaanalytic assessment shows a relationship between using cannabis during adolescence and later development of depression and suicidality,” he said.
“The major problem of this type of study is the difficulty in assessing causality — that cannabis causes later depression rather than subjects at higher risk of developing depression being more prone to use cannabis, for instance to cope with subsyndromic symptoms, even though in this study cases with prior depression were excluded.”