www.erowid.org
Use of marijuana is relatively safe. There are no confirmed deaths caused by marijuana alone, although deaths can and do result from injuries sustained while intoxicated. When combined with alcohol, cannabis has been shown to reduce driving ability and can contribute to traffic accidents.
Negative Health Effects: A list of health-related references can be found on the
Cannabid References Page. A very good introduction to the negative health effects of cannabis is the paper "Adverse Effects of Cannabis" by Hall W, Solowij N published in The Lancet, 1998 (14(352):1611-6). A brief summary of these can be found on the
Cannabis Basics Page.
Some people may experience panic attacks (including extreme feelings of dread, accelerated heart rate, feeling as if they're going to die) from smoking cannabis. [See the
Psychedelic Crisis FAQ for information about such an occurrence.]
Chronic smoking of marijuana can lead to respiratory ailments associated with smoke inhalation. A
1995 study suggests that use of a bong or water pipe does not necessarily lower the overall ratio of particulate matter to THC and may be counterproductive. In other words, it lowers the particulate matter, but it also lowers the amount of THC. For the same effects, a person may have to smoke more...thus raising particulate matter back to a level equal to that inhaled from unfiltered sources (joint or pipe).
Politics & Health: The political climate around cannabis and other recreational psychoactive substances has made it complicated to find balanced opinions about its safety and risks. The Federation of American Scientists has
an interesting article on the issue of cannabis-risks and the political motivation on those on both sides of the issue.