I did some digging into Leary's background and I think it's very relevant to my review of this book, so here goes:
The CIA created LSD and promoted both LSD and marijuana as ways to mind control or brainwash the masses. They also drugged unsuspecting people with LSD for their experiments. The promotion of such drugs, however, ultimately backfired with the effect of people rebelling and using them to deprogram themselves, and Leary was using it in therapy for people who were diagnosed with terminal illnesses so they could be at peace with their impending deaths.
Leary includes vivid, mystical poetry with his philosophical musings. The psychological connection to LSD becomes clear: The pineal gland in the brain produces DMT (the "spirit molecule") when one is dying, and DMT has a psychedelic effect much like LSD, and elicits dreams. Some people even take DMT while peaking on LSD.
For all his own personal journey of psychedelic exploration, Leary was interned in an insane asylum. It was thought he was brainwashed, since he made a complete 180 in his view regarding LSD. There's convincing evidence that prior to that he was a CIA agent, or at least was funded by the CIA. It doesn't really matter, though, because the message is still great. The most important takeaway is his motto,"Create your own religion."
Finally, Leary writes about how marijuana is enlightening on the physical and emotional level (it also slows down time), while LSD is enlightening on the cellular and even the DNA level. Very, very inspirational stuff.
This is a small book, but incredible nonetheless.