EVIDENCE SHOWS HEAVY MARIJUANA USE IMPACTS ON MENTAL HEALTH

KERRY O'BRIEN: Pot, dope, weed, herb, mull, grass -- we've got almost as
many slang words for it as we have for alcohol -- and that's because, even
though it's illegal, marijuana is also widely used.

It's been in common use for decades.

Over half of Australia's teenagers have at least tried it.

Yet experts admit very little is known conclusively about what effect it
has on mental health.

Significant research released by Victoria's Centre for Adolescent Health
today has added new weight to claims that heavy use of cannabis can cause
depression.

In Sydney, the issue was already a talking point, after the suicide of a
popular young Bondi surfer, whose mother publicly blamed his marijuana
habit for the depression that led to his death.

Sean Murphy reports.

GUNDI MITTON: When I wanted to give him a religious, a spiritual, we should
say, a spiritual teaching, he said, "Mum, when I'm in a tube, that's when I
communicate with God, that's when I'm closest to Jesus or God, whatever."

SEAN MURPHY: Marcel Mitton's love of the ocean was a constant, but so was
marijuana.

Outwardly, the 31-year-old was handsome, confident and popular, but behind
the bright smile and easy manner, Marcel's demons led him to take his own
life in a very public drowning at Sydney's Bondi Beach.

GUNDI MITTON (READING): "I'm not writing this letter to lecture to you, but
how to deal with your depression because covering up your despair instead
of reaching out for help gets you nowhere."

SEAN MURPHY: Gundi Mitton wrote this letter to her son before Christmas to
help him deal with depression, a suicidal depression which she now blames
on marijuana.

GUNDI MITTON: He smoked it daily, needed it to get out of bed, to get to work.

But never, never did I knew what a dangerous drug it was, what an addictive
drug.

That it demotivated the young people.

SEAN MURPHY: Marijuana's links with mental illness have been alleged since
prohibition of the drug in Australia, but even today, expert opinion
remains divided.

Based on the research that's been done till now, can you say whether
cannabis causes depression?

DR LOUISA DEGENHARDT, NATIONAL DRUG & ALCOHOL RESEARCH CENTRE: No, we can't.

What we can say is that there does seem to be an association.

PROFESSOR IAN HICKIE, beyondblue: People who use cannabis at high levels on
a regular basis, often on a daily basis, are at increased risk probably of
developing depression and certainly if they've got depression, they're at
increased risk of a worse outcome.

SEAN MURPHY: 39-year-old Gus Lee is building a home renovation business and
building a new life.

After 21 years of heavy daily smoking, he's overcoming a dependency which
led to suicidal depression.

GUS LEE: I would get stoned and I would have grand ideas of doing anything,
and a few hours later I'd still be on the couch, you know.

I wore out a couch, I wore out a remote control unit from laying there
daydreaming about all the wonderful things I was going to do.

I certainly had suicidal thoughts a lot of the time and acted on it a
couple of times and about five years ago, a serious suicide attempt which
had me end up in a psychiatric hospital.

SEAN MURPHY: According to beyondblue, Australia's national depression
initiative, the link between cannabis use and depression is most evident in
chronic users.

What the experts don't know though, is why some people can use the drug
recreationally while others become dependent.

PROFESSOR IAN HICKIE: We don't really understand all the factors.

We know some are genetic, we know some have to do with exposure, we know
some have to do with family and other social contexts, so some people are
clearly at risk.

Most people are exposed in their teenage years to alcohol, to nicotine, to
cannabis, and only some people go on to abuse those substances or become
addicted to those substances and clearly that group which does tends to
have higher rates of depression and anxiety.

SEAN MURPHY: What do you think about marijuana?

YOUNG MAN: It's -- it's green.

YOUNG WOMAN: Anyone that I know that's taken it is always pretty mellow.

YOUNG MAN 2: More people I know have problems from alcohol than from
smoking mull, so --

YOUNG MAN 3: Definitely, yeah.

I'm not innocent, I've smoked it, I didn't really get too depressed.

I'm sure if I got to that stage I'd stop.

SEAN MURPHY: At Perth's Big Day Out rock concert, these views were typical
of young opinions on marijuana.

Half of all Australian teenagers now admit marijuana use.

Experts acknowledge research into its long-term effects is seriously lacking.

DR LOUISA DEGENHARDT: When we initially started looking at this issue we
were surprised at how little there has been done on this subject and I
think it's definitely something that needs to be addressed in the future.

SEAN MURPHY: Louisa Degenhardt supervised Australia's most comprehensive
community survey on drug use and mental health.

More than 10,000 people were questioned.

DR LOUISA DEGENHARDT: People who are cannabis dependent can come from all
walks of life.

There's no particular area that they might live in or whatever.

In terms of people who are more likely to be depressed who are using
cannabis, they're more likely to be using other drugs as well.

SEAN MURPHY: A study of more than 2,000 teenagers over 10 years, released
today by Victoria's Centre for Adolescent Health, is providing the best
ongoing research into the link between cannabis and depression.

PROFESSOR GEORGE PATTON, CENTRE FOR ADOLESCENT HEALTH: So one thing we'd
really like to know is to what extent this is reversible once people stop
using heavily.

And this is something we hope to do in this study, asking the question --
if heavy users stop using, do we find the level of mental health problems
diminish?

If we find that, that's strong evidence again that it's cannabis use which
is causing the problem.

SEAN MURPHY: Marijuana was popularised in the 1960s and '70s.

But patterns of use have changed.

Today, teenagers are smoking the drug at a younger age and using bongs, or
water pipes, in search of a more potent high.

According to psychiatrist Professor Ian Hickie, parents who use the drug
themselves can have a false sense of security about their children's
cannabis use.

PROFESSOR IAN HICKIE: Their parents, a bit like their alcohol use, are
probably using the substance kind of episodically and recreationally, and
that would be their experience as teenagers.

But many teenagers we know are actually using the substance daily on an
ongoing basis and may continue that for some years and that's the pattern
of use which appears to be much more problematic in terms of depression and
suicide.

SEAN MURPHY: Dr Ray Seidler has been a GP in Sydney's Kings Cross for 24
years and has a special interest in substance abuse.

He believes the debate about marijuana and depression should focus on
suicide and the need for people to recognise the symptoms.

DR RAY SEIDLER, GP: In Australia, men don't do that.

Young men particularly don't want to talk about how they feel and I think
we need to encourage them to do that.

I think if people pick up increasing illicit drug use of any sort, or
alcohol abuse, a mood change, a loss of weight, a loss of interest in
previously-loved activities, a disinterest in going out, a kind of
isolationist attitude to the world, then they need to be aware that this
may well be an episode of severe depression.

SEAN MURPHY: More than 100 surfers farewelled Marcel Mitton in a touching
Bondi ceremony.

His death has posed many questions, but without further research, what
remains unanswered is if marijuana was a symptom of his spiralling
depression or its cause.

Answers which will come too late for Gundi Mitton, mourning the loss of her
only son.

GUNDI MITTON (Reading): "You can meet all the difficulties ahead of you
because you have what it takes.

Love Mother.

The sun will shine again."