I quit back in 1977... and I did it with my own method...
What i did was roll up a whole bunch of joints and put them in a cigarette package... then every time I wanted a smoke, I smoked a joint... After about a week, or two, I was then able to taper off the dope fairly easily...
I don't recommend this for everyone, but at the time I was semi-retired and had no commitments, lived in a dope friendly home and so it was easy.