Reddit reviews A Primer of Drug Action: A Concise, Non-Technical Guide to the Actions, Uses, and Side Effects of Psychoactive Drugs

A Primer of Drug Action by Robert Julien (http://www.amazon.com/Primer-Drug-Action-Non-Technical-Psychoactive/dp/080507158X)

Awesome book. He goes through drug class by drug class, explains effects on the body, drug-drug interactions, and even has a chapter on natural medicines. Very thorough!

There are many choices if you are looking for books that deal with drugs very directly. If you are looking information on the social aspect of drugs (i.e., what it is like for a person who doesn't care about the educational aspect of doing drugs to do drugs, including stereotypes of which people do which drugs, what stupid things people on drugs will frequently do, etc.), something like Fear and Loathing in Las Vegas would be good.

For a clinical perspective, understanding how drugs affect people physically, books about neurotransmitters and receptors and brain function and the like, A Primer of Drug Action has served me well, though it is a bit dated and is not written with the psychonaut in mind. There is certainly value to learning about non-recreational drugs, as there are a wide variety of things like anti-psychotics or steroids or NSAIDs whose usage isn't 'fun' but nonetheless are interesting from a neurobiological standpoint. For a further understanding of the brain in general, an intro neurobiology textbook might be advised.

I feel like many people have already put forth a good selection of philosophical books on drug use, so I will abstain from providing any more. The Doors of Perception, as already mentioned, is a fantastic place to start. Few other books have filled me with such reverence of psychedelics and the human mind.

Lastly, and most importantly, I would like to point out (warning, .pdf link) Prometheus Rising. It is not a highly drug-centric book, but if you are interested in doing drugs to better understand the self and the human mind, as well as to reach 'enlightenment' (whatever that may be), this book is possibly the most valuable tool for that purpose. I highly recommend that everyone read this, though I must suggest that you not take it so seriously because it is not meant to be read in an overly-academic or fact-oriented light. Much like a zen koan, it is meant to illuminate through 'shocking' the mind into awareness, albeit in occasionally ridiculous or offensive ways.