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Quotes in the image to the left (and in the text below) are from the U.S. government's landmark 1999 Institute of Medicine (IOM) report, Marijuana and Medicine: Assessing the Science Base. The full text of the report is available for free online at the above link, and is searchable. The table of contents by chapter is on the sidebar. The report is also available as a free PDF download. Quotes below are followed by their references. Emphasis added.
Page 109: "Indeed, epidemiological data indicate that in the general population marijuana use is not associated with increased mortality. 138"
Page 107: "When heavy marijuana use accompanies these symptoms [amotivation], the drug is often cited as the cause, but no convincing data demonstrate a causal relationship between marijuana smoking and these behavior characteristics. 23"
- 23. Chait LD, Pierri J. 1992. Effects of smoked marijuana on human performance: A critical review. In: L Murphy and A Bartke, Editors, Marijuana/Cannabinoids: Neurobiology and Neurophysiology. Boca Raton, FL: CRC Press. Pp. 387—424.
Page 119: "There is no conclusive evidence that marijuana causes cancer in humans, including cancers usually related to tobacco use."