I've been on propecia/rogaine for 10 years. I have smoked (until recently) fairly regularly since I was in my late teens (I'm 31). I can't say what propecia actually did for me.....it's hard to to know what i might look like if I hadn't taken it of course... All I know is that I have my hair. Only recently (still on Propecia. and rogaine) has my hair started receding again which is quite the FU. If anything, I suppose it's postponed my hair loss, but I'd have to say that if pot affected my hair, it would have long ago.
I think (and I'm no expert) that when we start to thin, we try to come up with a reason why it's happening. Am I not eating properly? exercising regularly? how's my circulation? Smoking cigarettes? Smoking pot? etc. etc. etc. I've certainly been doing that as of late when a few months ago, my hair started taking a turn for the worse. Sometimes, though, it just happens.... in fact, I think that balding just ALWAYS happens if it's going to happen. It sucks *** and i pray everyday that it stops RIGHT THERE, but it is what it is I guess.
I'd try to do the propecia thing if I were you. If it doesn't cause you any lewd side effects, it might help you some. As for pot, I hear a lot of different things, but as I said..... if it hurts your hair, I'd be bald like 10 years ago..... hard to say.