I know people who have drugs rule their lives.
I know people who partake recreationally regularly, and also infrequently.
The issue I have is, you don't know if one will turn into the other (and the first kind never turns into the second kind!), nor do they.
Ask him what would happen if he couldn't continue this lifestyle, for example, the money ran out, or he had a health condition that meant it'd kill him, quickly and without much warning.
I use cannabis (edibles) occasionally, sometimes for amusement much as others might have a glass of wine, sometimes for pain relief. I can go months without using any and then have some several weekends in a row. Then I might go YEARS without any... etc etc. I never work whilst stoned, I don't rely on it on a daily basis to get me going or calm me down or whatever, and if I could never have any again I would not care.
But that is not particularly usual, and is probably closely related to the fact my partner also isn't particularly bothered either - if I were surrounded by people doing it daily, I may well do it more (though.. back in the days when I was, I didn't... but people change).
Lifestyle and peer groups are as important here as the drug use - I have never been part of a social group that puts any pressure on anyone to use. Whilst I have been part of groups who DO use and use varied substances and frequently, there was never any 'you have to or you can't be in the group' about it and i am not the sort of person who really cares if I am doing what others are doing.
If he can't leave that lifestyle and social group... then it wouldn't really matter what drug he was using, even if it were legal, he wouldn't stop.