Despite anti-drug education campaigns which state marijuana is a gateway for harder drug use, new research from the University of New Hampshire says for most people that's not true.

But pot does serves as a "gateway," says Dr. Karen Van Gund, associate professor of sociology., mainly for young people who are poor, unemployed, and subjected to severe psychological stress.

In other words, the path to other drugs is not necessarily the pot, but rather the potholes young people encounter on the road.

Can marijuana make you crazy? Not according to the scientific literature, which finds scant evidence that marijuana causes mental illness.

Some users do experience anxiety and paranoia, and too much weed can cause toxic psychosis. That's when you lose contact with reality. The effects are temporary.

The National Institute on Drug Abuse (NIDA) says that although depression, anxiety, and personality disturbances are linked with chronic use, it is not clear whether pot causes those problems or is used to "self-medicate" against them.

Marijuana is good for glaucoma. There's no debate about that, but the American Academy of Ophthalmology says there is no reason to believe that marijuana is any better at treating glaucoma than FDA-approved medication.

And in some ways, typical medication is better because it can be delivered in controlled doses. It's hard to know how much THC (the active ingredient in weed) you get from smoking a joint.

It seems logical that smoking weed could lead to lung cancer: The American Lung Association says pot smoke has more carcinogens than cigarette smoke. Pot smokers also tend to inhale more deeply and hold the smoke in their lungs longer than tobacco smokers do, which increases the lungs' exposure.

But the evidence, at this point, doesn't seem to back up the theory. A large study in 2006 found no link between weed and lung cancer - this to the surprise of the UCLA research team, whose members expected to find a correlation.

Marijuana may not be physically addictive like nicotine, but many experts agree that it can become a habit that's very hard to break, especially after long-term use. Addiction, as defined by the National Institute on Drug Abuse, is compulsive use even when the user says it's getting in the way of home, work or school.

The jury is still out on whether or not marijuana impairs the immune system.

According to the National Institutes of Health, research shows THC has a negative effect on various immune cells, but there are no human studies to date which connect that effect with increased infection.

A 2002 study found that marijuana certainly has an effect on the immune system, "however, because of the complexity of the immune system, we can't say yet whether the effect we've observed in humans is good or bad," UCLA scientist Thomas Klein wrote.

Animal research seems to suggest trouble, but the NIH says the matter warrents more research.

On the federal level, weed advocates shouldn't hold their breath for decriminalization. True, in January 2009, the American Medical Association announced that the federal government should consider reclassifying weed.

This was done in the hopes of making it easier for researchers who want to study medical marijuana to get their hands on enough of it. This is an issue, because pot is a Schedule 1 controlled substance. That means it's in the same category as heroin.

Still, the AMA states that they do not think there is evidence that marijuana "meets the current standards for a prescription drug product."