(question from George)
THC, the active ingredient of cannibus/marijuana, certainly has a definite affect on one’s dreaming. However, insomuch as THC itself affects different people in different ways, the effect of one’s dreaming will vary from individual to individual too. Some scientific studies have shown that REM periods are reduced or suppressed by THC, and though unfortunately these are quite old, there is plenty of anecdotal evidence supporting this too. While some people may experience vivid dreams shortly after use, generally, most people (again, not all) who smoke or ingest pot find that they have more trouble remembering their dreams, or even a complete lack of dream recall.
One likely cause of this is that THC builds up in the Hippocampus area of the brain, which has been identified as relating to dream interpretation and short-term memory, resulting in less dreaming or less dreaming memory. How quickly this happens, whether with one-time or regular use, is probably different for everyone, though with abstinence, full capacity generally returns in about a week. Personally I don’t go near pot any more, not because I have anything against it, but because I enjoy my dreaming far more. So for some of us it may come to a choice between the two.
When it comes to lucid dreaming, obviously having an impairment of one’s dreaming memory is going to be a bit of a problem, since memory is one of the foundations of lucidity. But for those who want to both smoke marijuana and lucid dream, it may be a worth trying some other herbs to counteract this undesirable side effect… A herbal tea before bedtime of Mugwort (known to increase the vividness of dreams) and Ginko Biloba (known to improve memory) may prove beneficial. In fact, I would recommend trying this whether you smoke or not! These two common herbs will give a nice boost to your dreaming.
Hope this helps! If you want to read more details on studies of THC on REM, check this forum thread (not exactly light reading though.)