Big risk to female cannabis smokers

By MARTIN JOHNSON

Young women who smoke lots of cannabis are seriously risking depression, new research shows.

Women using the drug daily - which is considered heavy use - run seven times the risk of suffering depression and anxiety, a major Australian study reports.

The researchers say it is the strongest link yet between heavy cannabis use and depression and raises treatment issues for doctors involved with users.

A similar study of both sexes by a Christchurch Medical School professor found that daily use of cannabis doubled the risk of depression.

The leader of the Australian team, Professor George Patton, of Royal Children's Hospital in Melbourne, said the risk for young men was twice as high as for non-users.

The hospital's Adolescent Health Centre, which he heads, followed 2000 young people for seven years from the ages of 14 to 21.

"We found that around two-thirds used cannabis at some point between 14 and 21," he told the Herald last night.

"Those who were using less than weekly didn't appear to have any greater risk of mental health problems, but as they moved from weekly to daily use they ran into high rates of cannabis dependence."

Cannabis has long been associated with mental illness, but Professor Patton said research had focused on links with schizophrenia and psychosis.

"Talk to long-term users and they say one of the downsides is the level of depression they attribute to their cannabis use."

But it had been uncertain whether they used cannabis because they were already depressed, or whether the drug caused the depression.

"This is the first evidence to date that I'm aware of that the link is from cannabis to depression."

Professor David Fergusson, of Christchurch Medical School, said last night that his study of 1265 people in the city from birth to age 21 had found that daily cannabis users were up to twice as likely to become depressed. The risk for heavy alcohol users was slightly higher again.

He thought the link between cannabis and depression was weaker than in the Melbourne study because he had followed his subjects for far longer.

This was a strength of his study because it had permitted more influences on a person's life to be considered, such as his or her childhood.

"One of the alternative explanations why heavy cannabis-using young people develop this [depression] is that they come from difficult backgrounds - disadvantaged, dysfunctional childhoods."

His study will be published in the British journal Addiction this year.

Professor Patton said the degree of depression among Australian users revealed by his study was such that their GPs should be doing something to lower it.

"Cannabis use aside, the GP would be considering psychological counselling and in some instances treatment with medication."

In New Zealand, 52 per cent of the population aged 15 to 45 have experimented with cannabis, said a report in the Medical Journal last year.

Use was higher among men but was increasing among women.

About 20 per cent of that age group were current users, defined as having used the drug in the past six months.

nzherald.co.nz/health