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ADVICE: I recently discovered a small bag of marijuana in my 17-year-old son's bedroom. I'd had my suspicions for a while. I confronted him about it and he said smoking pot is something he only does occasionally and that it's "better than drinking" for his health. I don't agree. I've worked with dope smokers in the past and found them brain dead. My son is intelligent with a bright future. I'd hate to see his grades start slipping at this point. But I'm a single working mum and he's always been very independent. How can I stop this?

When you confronted your son about the bag of marijuana, he gave you an intelligent reply and it sounds as if this is a boy you can reason with. He said he only smokes pot occasionally, so at least you know what you are dealing with.

If he's suggesting that marijuana is better for his health than alcohol then he is right, but in a limited way. It's possible to die from binge drinking and it can happen very quickly after consuming large quantities. You won't die from excess marijuana but the impact will nevertheless be there over time.

When you're 17, you can't imagine the repercussions of a conviction on your life, the risk of triggering a mental illness or the possibility of long term brain damage. The information regarding the effects of cannabis on the teenage brain are extensive and you are right to be concerned.

Convincing your son to look far into the future is made harder by the fact that his reasons for smoking cannabis will be about how he's feeling right now. Usually teenagers start their habit because of peer pressure and social acceptance. There is an immediacy about their choice that makes your rationale for looking into the future so much more difficult.

So, when you ask, how can I stop this? I think you should do what you're doing. You've confronted him and opened up a discussion. Talk about the possibility of him becoming addicted or losing his way (although try not to be too alarmist in these discussions as that will widen the gap between your perspectives). Make it clear that, regardless of what he does in his leisure time with his friends, studying and achieving his academic potential is essential in your home. If he's the boy you think he is, then he'll process your thoughts, focus on his bright future, and the marijuana will fade into the background.

Mary-anne Scott has raised four boys and written two novels for young adults including 'Coming Home to Roost.' As one of seven sisters, there aren't many parenting problems she hasn't talked over.

- Stuff.co.nz