Marijuana has 400 chemicals, so it is dangerous

    This is another scare tactic used by many ignorant people. The general accusation is that the more chemicals a substance has, the more dangerous it is. For example, coffee has over 800 chemicals.(1) Rat poison has about 30. It only takes one chemical compound, like cyanide, to kill you. Any chemist will confirm that the chemical-count of any substance is not related to it's properties. A complete list of the chemicals in marijuana is available (4), and only 66 are psychoactive cannabinoids. The rest are common to many foods, vitamins, minerals, etc., having no psychological effect on humans. See Chemicals.

    The fact that there are over 60 unique chemicals in cannabis, called "cannabinoids", is something that scientists find very interesting. Many of these cannabinoids may have valuable effects as medicine. For example, "cannabinol" is a cannabinoid which can help people with insomnia. Doctors think that this chemical is why most patients prefer to use marijuana rather than pure Delta-9-THC pills (called dronabinol) -- the cannabinol takes the edge off being `high' and calms the nerves. Another cannabinoid, "cannabidiolic acid", is a very effective anti-biotic, like pennicillin. Many of these chemicals can be extracted from marijuana without any fancy laboratory equipment. (2)(3)

Sources:

1. "Too Many Rodent Carcinogens Mitogenesis Increases Mutagenesis" by
B. N. Ames, L. S. Gold in ``Science'' Vol. 149 pp. 971. ed. pub.,
1990.

4. http://www.thedrugwar.com/medicinal-marijuana/22545-chemical-constituents-cannabis.html