I do this sometimes. It's cool....its exactly like smoking a cig, but it gets you fucking high. Its great.

What i do is gently twist the cig, so it loosens the tabacco and it should slowly fall out. (I always leave half a cm of tabacco in the cig so weed isnt wasted). I then just put weed in the emptied cig. Now here is the trick. Put the weed in it slowly and get a EAR COTTON BUD CLEANER THING....and as you put the weed in it....stuff the weed down with the cotton ear bud thing and make it as tight as you want it (depending on how hard you stuff the weed down).

Mine always end up just like a normal cig. Except it burns a little bit faster.