Here is an exert from the wikipedia entry:

Marijuana is is a psychoactive product of the plant Cannabis sativa. The herbal form of the drug consists of dried mature flowers and subtending leaves of pistillate ("female") plants. The resinous form, known as hashish, consists primarily of glandular trichomes collected from the same plant material. The major biologically active chemical compound in cannabis is Δ9-tetrahydrocannabinol (delta-9-tetrahydrocannabinol), commonly referred to as THC.

Cannabis has psychoactive and physiological effects when consumed, usually by smoking or ingestion.

If you're interested in reading more of that, copy and paste this link into your browser:

http://en.wikipedia.org/wiki/Cannabis_(dru g)

Now, you should know that there are a lot of misconceptions about Marijuana. I myself smoke Marijuana every day and usually buy it by the ounce (which costs between $100-$120/oz where I live, just to give you an idea). I'll tell you a little bit about my experience with Marijuana:

I used to be against drugs, including Marijuana. One night, I took some pills with friends and got very...messed up. When I woke up the next day, my friends told me that I had smoke Marijuana with them. I was kind of shocked, but I didn't remember what happened the night before so I didn't know if I had enjoyed it. So, I decided that, since I had tried it already anyway, I was going to do it again to see what it was like. I smoked a blunts worth (about the size of a cigar) between three people, which is quite a bit for someone with no tolerance. I became extremely relaxed and found myself twitching uncontrollably. As the days went by, I started smoking large amounts of Marijuana every day, and after I developed a bit of a tolerance I didn't get nearly as high as I did when I first started (I was pretty much comatose). Anyway, after awhile I started trying different ways to smoke it (there are SO many: joints, blunts, pipes, one-hitters, and various types of bongs). I have found that what you smoke out of effects what kind of high you will have, and how much THC you will actually absorb. One other factor that will effect your high is what kind of Marijuana you smoke. After awhile, I started smoking keinbud which is very expensive but very potent.

Anyway, sorry for rambling. To get to the point, a psychoactive drug is a chemical substance that acts primarily upon the central nervous system where it alters brain function, resulting in temporary changes in perception, mood, consciousness and behavior. These drugs may be used recreationally to purposefully alter one's consciousness, as entheogens for ritual or spiritual purposes, as a tool for studying or augmenting the mind, or therapeutically as medication.

I have experienced hallucinations while on Marijuana, but that may be partly because I have a history of psychiatric problems, including psychosis.

Mairjauna is officially both a stimulant and a depressant. It does not have hallucingenic effects.

Yes, but what is made official and what is actually true are usually two completely different things, especially in th USA. Believe what you want, people, but you have been deceived by your government concerning marijuana and I don't think anyone who doesn't have much experience using it has a right to say what it does or does not do.

FYI: All of my friends smoke marijuana, and all of them have reported hallucinations at least once while under the influence of it.

That isn't necessarily true. Marijuana can act like a conventional hallucinogen (somewhat similar to magic mushrooms or LSD) if taken in a considerable oral dose, perhaps even a huge smoked amount. The term hallucinogen is controversial in itself however. Hallucinogen would seem to imply that it creates hallucinations i.e. what isn't there. This isn't necessarily the case because conventional hallucinogens distort visual fields, it doesn't alter them (discounting overdosing and resulting Hallucinogen Persisting Perception Disorder - HPPD). I prefer to use the term psychedelic in regards to marijuana.