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The Reds Super Rugby coach told rugby.com.au that his brother-in-law battled with substance abuse years ago and it provided Thorn with a glimpse into the way drug use can ruin lives.
He has taken a tough line on players James Slipper and Karmichael Hunt who have had issues with drug abuse affecting their careers.
"When you're talking about cocaine to me, it's a serious issue," he said.
"I know that probably these days people are saying it's more prevalent but once again, it's the Queensland Reds - this is part of the Queensland Rugby Union.
"I don't want [cocaine] to be around this team, this club or the kids around this club.
"I'm a dad - I've got four kids and on my wife's side one of her siblings had some issues with drugs and it's a tough thing.
"I know they call them party drugs and stuff now but you can call them whatever you want - they cause issues in people's lives.
"I don't really want to talk about it too much because I want to respect my wife and her family - my family - I guess.
"But the good news is, he got through that.
"It's not great for society, it's talked about in the newspapers and it's a challenge for society."
Taking a hard line stance on that challenge, as Thorn put it, is not about making an example of Hunt and Slipper.
It is setting an example for the players he has nurtured. And he doesn't want them straying into habits that have left Slipper and Hunt without Super Rugby contracts.
"There are a lot of young guys coming through and it's important to me that they have good mentoring from myself or that the club culture is strong," he said.
"As much as I want them to go on to be great players and have great careers, I also want them to be great people and humble.
"So kids have good role models when they see a Reds player - he plays good footy and someone that the way he goes about his stuff shows good qualities.
"We've all got our battles and I'm not saying everyone has to be perfect or anything but as a dad with four kids of my own, there is the footy side of things and then there is the people side of things.
"I'm hoping that there is a long term - that we are working towards building a foundation for a long term healthy club and rugby in Queensland and hopefully some success - that's my mindset."