*Sigh* I'll give this a go:
It is my understanding that THC is naturally produced in humans, and your CB-1 and CB-2 receptors are the ones that allow THC to bind to them. I am under the impression they are near your hippocampus, or the place where you store short-term memory. Your brain interprets short-term memory while you dream, but if you are high, you don't remember (your short term memory is somewhat fried). This has nothing, or very little, to do with REM sleep cycles or stage 2/3.
To clear things up:
CB-1 regards a naturally occurring chemical in the body known as Anadamide -- often called Naturally Occurring Cannabinoid Compound (similar to THC).
CB-1 receptor refers exclusively to the dendrite of a nerve cell which binds the fatty molecule metabolized THC.
What is the point of naturally occurring THC in the body, you might ask? Well, the best guesses and research I've heard (on various boards and in psyc classes), is to protect the body from stroke, concussions, or any sort of trauma to the head. Also, it helps us during prolonged stress due to lack of sleep or related variables. This is just best-guess work at this point, though, but you can see how it may figure into sleeping.
Since THC is now known to be naturally occurring, it could be that smoking weed may eliminate the need for as much REM sleep as we would normally have. This is odd, though, as REM sleep is where the body gets the majority of it's healing and rest done (studies have found that waking someone up before REM sleep cycle yields... well... sleep deprivated insanity). If weed were to actually lower the amount of REM sleep, I think it would be noticeable, right? Well, when you quit smoking, you get intense dreams, which some attribute to the body "re upping" your natural THC levels.
Based on the fact that we do (I assume all of us here) smoke weed and still get REM sleep (as have generations upon generations before us), I don't think you have much to worry about. Heavy habitual use could produce a dependency upon weed until your body gets used to producing it's own THC again, though, but this seems to be a short-lived withdrawal symptom of VERY HEAVY users.
So, to answer your question: I do not think it inhibits REM sleep so much as our body needs -less-, or thinks it needs less. If it actually did inhibit REM sleep to a significant (scientifically speaking) degree, we would have noticed it by now. Cannabis does have ZERO toxicity and zero deaths strictly due to use (though I'm sure you could suffocate), it's actually safer than a lot of food you may consume on a daily basis.
Does unnaturally occurring THC interfere with REM sleep? Yes. How? Science doesn't seem to quiet know yet. Is it bad? It might be - but to what degree or in what way, that isn't really known. All we *really* know right now is that there is a causal effect. However, this effect does help a lot of people with over-active REM dreaming or night terrors. Perhaps this is a good thing? It was also suggested, once upon a time, that smoking reduces the lubrication in your eyes, so during REM... well... draw your own picture.
To best honest, isn't science still a bit confused about what REM sleep really is? What is the purpose of dreaming, or rapid eye movement anyway? To say that effecting dreams is good or bad assumes that you have full knowledge of a topic you can't possibly have knowledge of at all.
I suggest you look up reports on PsycINFO -- it's an amazing database with a very robust amount of research information that has been peer edited and reviewed. A lot of the info tends to be outdated when you look into drugs though, as a bulk of it was done in the 70s and was funded by the government (Read: Heavy Bias). It is important when looking up publicated research that you understand that ANY research done through a college (a lot of it) is GOVERNMENT FUNDED, STAMPED, AND REPORTED TO. There is still an agenda, but that doesn't mean all the information is bad.
Also consider that cannabis isn't made solely up of THC, but has other properties like CBD and CBN which may effect sleeping. Food for thought
