In my opinion it depends on you the individual.
i havent seen marijuana have a negative effect on my weight training. dont work out when ur stoned, i tried it one time and it completely killed my high and my workout didnt seem as productive.
i smoke everyday and began working out maybe 7 or 8 months ago. i go 4 or 5 times a week and try to eat "right", and i have gained muscle mass and strength. my work out partner doesnt smoke and as far as lifting goes were are neck and neck.
what i do that might help u is to smoke at the end of ur day. as the other poster said you can definitley feel it in the muscles you worked out.
and remember to see good gains in mass, you need to eat more protein. especially after a workout, it helps ur muscles recover.