I wasn't at all surprised to learn this week that kids who start smoking dope at a young age suffer long-lasting harm to their IQ.

As someone who works in talk radio, and who has had to try to decipher the logic and rationale behind young, predominantly male, dope-smokers pleading the case for decriminalisation of cannabis, I'd long suspected the damage caused by dope was significant and irreversible.

And before those who enjoy a gentle toke of an evening leap up and down and point to the ramblings of alcoholics whose brain cells have been nuked by the drink, I agree.

Long-term substance abuse of any kind will leave you with brain damage. But it's the damage cannabis does to young minds that is most concerning.


Researchers have analysed more than 1000 Kiwis who have been part of a study that has tracked them since their birth in the early 1970s.

These sorts of longitudinal studies are a rich vein for researchers and scientists to mine, and the evidence is incontrovertible.

Of those participants who took up cannabis in adolescence and used it regularly for years afterwards, there was an average decline in IQ of eight points when measured at age 13 and at 38. People who didn't begin smoking dope until much later, when their brains were fully formed, didn't suffer the same decline. The decline couldn't be explained by alcohol, other drug use or having less education, according to the team of international scientists.

The higher the IQ, the better the education, the income and an individual's health - so a loss of eight points is significant.

The results of the study will also come as no surprise to teachers around the country. Ask them whether dope smoking impairs teenage learning and they could give you thousands of stories of bright young kids full of potential deteriorating into apathetic stoners.

The teenage brain is vulnerable and needs to be protected from all harmful substances.

But because the teenage brain can't process consequences, it will be difficult to get the message through to them that they need to wait before indulging in recreational drugs of any sort.

When you're 15, the age of 38 might as well be 108.

I wish that instead of a study that says cannabis is harmful to a young brain, researchers would turn their attention to how we can successfully protect young people from their own risk-taking selves.