His comments come in the wake of five New Zealand Warriors players being disciplined recently for mixing prescription drugs with energy drinks.
“It can happen in any sport,” Merrin said, according to the New Zealand Herald.
“It’s a bit of an issue but you can’t really control it — it’s one of those uncontrollables in the game.
“You can deliver a message about what can come from these kind of things but at the end of the day it falls back on the individual and what they want to do.
“The message is out there to stay away from it but it falls back on the individual and the consequences are their own.”