Pennsylvania Governor Shafer did a study in 1971 for Nixon.  Shafer recommended decriminalization. Nixon shredded his copy. “Findings of the National Commission on Marijuana and Drug Abuse include:
– “No significant physical, biochemical, or mental abnormalities could be attributed solely to their
marihuana smoking.” (National Commission on Marihuana and Drug Abuse, “Marihuana: A Signal of
Misunderstanding; First Report, Washington, DC, U.S. Govt. Print. Off, 1972, p. 61)
– “No valid stereotype of a marihuana user or non-user can be drawn.” (p. 36)
– “Young people who choose to experiment with marihuana are fundamentally the same people, socially
and psychologically, as those who use alcohol and tobacco.” (p. 42)
– “No verification is found of a causal relationship between marihuana use and subsequent heroin use.”
(p. 88)
– “Most users, young and old, demonstrate an average or above-average degree of social functioning,
academic achievement, and job performance.” (p. 96)
– “In sum, the weight of the evidence is that marihuana does not cause violent or aggressive behavior; if
anything marihuana serves to inhibit the expression of such behavior.” (p. 73)
– “In short marihuana is not generally viewed by participants in the criminal justice community as a major
contributing influence in the commission of delinquent or criminal acts.” (p. 75)
– “Neither the marihuana user nor the drug itself can be said to constitute a danger to public safety.” (p. 78)
– “Recent research has not yet proven that marihuana use significantly impairs driving ability or
performance.” (p. 79)
– “No reliable evidence exists indicating that marihuana causes genetic defects in man.” (p. 84)
– “Marihuana’s relative potential for harm to the vast majority of individual users and its actual impact on
society does not justify a social policy designed to seek out and firmly punish those who use it.” (p. 130)”

http://www.csdp.org/research/shafernixon.pdf