San Spirituality : Roots, Expression, and Social Consequences by David Lewis-Williams (discusses their use of medicinal plants as well).

At the intersection between western culture and Africa, we find the San people of the Kalahari desert. Once called Bushmen, Eminent anthropologists David Lewis-Williams and David Pearce present a balanced view of the spiritual life of this much-studied people, examining the interplay of their cosmology, myth, ritual, and art.