We see the most vivid dreams during the REM sleep stage, so that raises the question whether marijuana affects the stage of REM sleep. A study conducted in 1975 (Feinberg, I., Jones, R, Walker JM, Cavness, C, March, J. Effects of high dosage delta-9-tetrahydrocannabinol on sleep patterns in man) compared the sleep patterns of heavy marijuana smokers with those of non-smokers. The results showed that smokers have a lower speed of eye movement, and their REM sleep is very slow, which reduces the ability to see dreams.
Since marijuana tends to suppress dreams, when you withdraw it, dreams come back with a vengeance. It can be brightly colored, emotionally-rich dreams or nightmares, sometimes perceived as reality. Waking up and then falling asleep again, you find yourself in the same dream again. These vivid dreams usually occur every night about a week after the rejection of the drug and last about a month and then gradually taper off.
Thus, there is scientific evidence that marijuana smoking is closely related to one’s inability to dream, so the next time you smoke and can’t remember if you dreamed anything, you will know the answer to your question. 🙂