I recommend David Nutt's Drugs Without the Hot Air [1] on the subject. Nutt, a British psychiatrist and neuropsychopharmacologist, headed up the U.K.'s Advisory Council on the Misuse of Drugs (a British DEA/FDA hybrid). He was canned when he suggested that alcohol may be more damaging than many controlled substances.

Amongst the goodies from the book are this chart [2], which plots dependence risk against toxicologists' ratings of physical harm for various psychoactive substances. Nutt memorably compared the "20 drugs considered in the ISCD’s 2010 report, ranked by overall harm" with their legal Class and "found a correlation of 0.04 – which means that there was effectively no relationship at all."

Also: "Francis Crick, who discovered the double helix structure of DNA with James Watson, and Kary Mullis, who invented the polymerase chain reaction (PCR), had both taken [LSD], and attributed some of their understanding and insights to it."

[1] http://www.amazon.com/Drugs-Without-Hot-David-Nutt/dp/190686... Drugs Without the Hot Air: Minimising the Harms of Legal and Illegal Drugs by David Nutt

[2] http://upload.wikimedia.org/wikipedia/commons/9/9c/Rational_...

If you are interested in these kinds of things, you might find David Nutt's book interesting: http://www.amazon.com/Drugs-Without-Hot-David-Nutt/dp/190686...

It's perhaps a little UK-centric, but I found it well argued and the author is eminently credible.

MP "You can't compare harms from a legal activity with an illegal one."

Professor Nutt "Why not?"

MP "Because one's illegal."

Professor Nutt "Why is it illegal?"

MP "Because it's harmful."

Professor Nutt "Don't we need to compare harms to determine if it should be illegal?"

MP "You can't compare harms from a legal activity with an illegal one."

http://www.amazon.com/Drugs-Without-Hot-David-Nutt/dp/190686...

Nutt also wrote a pretty solid book about the data on the harms of various drugs (legal and illegal), and how best to reduce that harm as a society.

http://www.amazon.com/Drugs-Without-Hot-David-Nutt/dp/190686...

edit: Economist review of said book: http://www.economist.com/node/21560223