In my experience you need a pretty high tolerance and smoke pretty regularly for it to start preventing dreaming. When I intentionally reduced my tolerance to very low levels I started having dreams again.
As someone with a tolerance, I've learned that consuming too close to bedtime will cause me to have difficulty falling asleep, and also not enter REM sleep.
However, by consuming throughout the day on a daily basis but stopping by late afternoon or early evening, my sleep and dreaming is vastly improved.
This was how I functioned before I intentionally dropped my tolerance down to very low levels. With a lower tolerance I can enjoy the ganj as a nightcap and have all my dreams :)
