* Marijuana contains more than 400 chemicals, including most of the harmful substances found in tobacco smoke. Smoking one marijuana cigarette deposits about four times more tar into the lungs than a filtered tobacco cigarette.

This is flat-out false. The harmful chemicals in most tobacco, especially standard cigarettes, is the pesticides, herbicides, and other chemicals used on the tobacco plants to keep them alive. Tobacco is an extremely weak plant: Either lots of care or lots of chemicals must be used to keep them alive, and if a tobacco farmer has a whole field of tobacco plants, chemicals are the only choice that'll work economically. Cannabis, however, is a very sturdy plant (Why the colonists in America were so set on growing it), and doesn't need those chemicals, and they are very rarely used because of this.

* Harvard University researchers report that the risk of a heart attack is five times higher than usual in the hour after smoking marijuana.

This is probably true, but if you're already at risk for heart attack, you shouldn't be smoking cannabis. Smoke, but smoke responsibly. Just because some people are morons doesn't mean everyone who uses cannabis is.

* Smoking marijuana also weakens the immune system4 and raises the risk of lung infections.5 A Columbia University study found that a control group smoking a single marijuana cigarette every other day for a year had a white-blood-cell count that was 39 percent lower than normal, thus damaging the immune system and making the user far more susceptible to infection and sickness.

While I've never heard of this before, I would question the validity of the test subjects used within this study. Since Cannabis is obviously illegal, the study team couldn't have been providing the cannabis to the test subjects. This leads me to wonder how truthful the subjects were being, and how many other variables in their life the study team wasn't accounting for.

Just felt like adding my $.02 worth :dance: