This article presents proven, promising, and potential therapeutic uses for cannabidiol (CBD) in the treatment of psychiatric and neurologic conditions and diseases. It presents popular, but scientifically unproven health and therapeutic claims of CBD supporting the beneficial homeostatic effects of the intrinsic or endogenous cannabinoid system. It includes a review of cannabinoid pharmacology; it compares properties and the legal status of CBD and THC (delta 9-tetrahydrocannabinol) as well as the hemp and marijuana varieties of , and it reviews the historic 2018 U.S. Food and Drug Administration approval of Epidiolex, an oral solution of cannabidiol for two rare treatment-resistant childhood epilepsies, as the first -derived drug. We reviewed literature on cannabidiol, CBD, the endocannabinoid neuropharmacology system, and hemp and marijuana varieties of . The proven and promising medical uses and deficiencies of unproven health claims for CBD, legal implications for -derived drugs, and comparisons of CBD and THC and hemp and marijuana are summarized objectively with pertinent references. CBD and CBD and THC combinations have potential to provide safe, effective therapy for several psychiatric and neurologic conditions and diseases. However, such achievement will require a uniform standard of CBD purity and strength, and corroboration from adequately large and rigorously controlled clinical research studies.