As for marijuana, I'm not completely sure it effects hair growth. I've partaken in the substance since about 5th grade, and always had a little more facial hair than the guys in my class. I'm almost 19 now and have a pretty decent full beard, so I don't think it inhibits growth. However, the lack of oxygen from smoking it and tobacco may kill brain cells, and since hair is made of dead brain cells and proteins, it increases it? I'm not sure. I just know that the urge to shave is definitely deadened if I'm smokin' bud.

Your mind has to be stronger than your beard growth to actually be able to grow one.