Just in case you are planning a 5th edition, here are some suggestions for improvements:
P. 12 "Oldest know drawing of cannabis"
"In the literature on cannabis, this illustration from a very early manuscript of the medical teachings of Dioscorides is usually considered one of the earliest depictions of the plant. In all likelihood, however, the illustration actually shows the Chaste tree (Vitex agnus-castus), a plant common throughout Greece and that, on superficial examination, is indeed easily confused with cannabis."
Marijuana Medicine, Christian Ratsch, 2001, p. 89
P. 107 "Dr. Abby Hofmann"
The text above this illustration of Abbie Hoffman discusses Dr. Albert Hofmann, so I believe you are confusing the two. There is no "Dr. Abby Hofmann".
This is what Wikipedia says at the top of it's Albert Hofmann page:
"Not to be confused with Abbie Hoffman."
"Albert Hofmann (January 11, 1906 – April 29, 2008) was a Swiss scientist known best for being the first person to synthesize, ingest and learn of the psychedelic effects of lysergic acid diethylamide (LSD). Hofmann also was the first to isolate, synthesize and name the principal psychedelic mushroom compounds, psilocybin and psilocin . He authored more than 100 scientific articles and a number of books, including LSD: My Problem Child. He was named #1 out of 100 in Telegraph's magazine 2007 "Top 100 Living Geniuses" list."http://en.wikipedia.org/wiki/Albert_Hofmann
"Abbot Howard "Abbie" Hoffman (November 30, 1936 – April 12, 1989) was a political and social activist who co-founded the Youth International Party ("Yippies").
Hoffman was arrested and tried for conspiracy and inciting to riot as a result of his role in protests that led to violent confrontations with police during the 1968 Democratic National Convention, along with Jerry Rubin, David Dellinger, Tom Hayden, Rennie Davis, John Froines, Lee Weiner and Bobby Seale. The group was known collectively as the "Chicago Eight"; when Seale's prosecution was separated from the others, they became known as the Chicago Seven. While the defendants were initially convicted of intent to incite a riot, the verdicts were overturned on appeal.
Hoffman came to prominence in the 1960s, and continued practicing his activism in the 1970s, and has remained a symbol of the youth rebellion of that era."http://en.wikipedia.org/wiki/Abbie_Hoffman
In general, including 1) the author, 2) title, 3) year of publication and 4) page number of the sources of all your quotes directly underneath the quote would improve the utility of the book, as the current lack of complete notation makes it difficult to use the bibliography to match the quote with the source.