I recently obtained the following two volume set published in 2014 that covers a wide spectrum of entheogen material:
Ellens, J. Harold, ed. 2014. Seeking the Sacred with Psychoactive Substances: Chemical Paths to Spirituality and to God, Oxford: Praeger.
Volume I - History and Practice
Volume II - Insights, Arguments, and Controversies
Wide variety of excellent essays and research results, including such as:
"The Magic and Ceremonial Use of Cannabis in the Ancient World" (Bennett)
"Psychedelic Use and Contemporary Buddhist Practice" (Fadiman)
"Psychedelic Research: Past, Present, and Future" (Stanislav Grof)
"The UDV Religion, Science, and Academic Research" (Labate and Melo)
"Reflections on the Mystery of Death and Rebirth in LSD Therapy" (Christopher Bache)
"Psilocybin Research at John Hopkins: A 2014 Report" (Jesse and Griffiths)
and a great deal more (about 800 pages in two volumes)
Pricey, but it is also available on the web in ebook form.