Need Help - Staking/Smoking Pot Question

[playtowin]

I am currently staking a close friend of mine. After agreeing to stake him, I also asked that he does not smoke pot while playing. He said that he believes that smoking pot has no negative influence on his game, and that I shouldn't worry about it (citing a few top players on this forum as an example). Should I make this an issue, or should I not even worry about it? Thanks guys.