In nature, Cannabis ruderalis typically has the lowest levels of THC, Cannabis sativa has a higher level of THC than it has CBD, and Cannabis indica has a higher level of CBD than it has THC. However, since man has been cultivating cannabis (and especially Cannabis sativa) for thousands of years, the effects of artificial selections have led to several different types of cannabis even within the same species, depending on the purpose the cannabis was cultivated for.
Various strains of "medical marijuana" are found to have a significant variation in the ratios of CBD-to-THC, and are known to contain other non-psychotropic cannabinoids. Any psychoactive marijuana, regardless of its CBD content, is derived from the flower (or bud) of the genus Cannabis. As defined by U.S. federal law, non-psychoactive hemp (also commonly-termed industrial hemp), regardless of its CBD content, is any part of the cannabis plant, whether growing or not, containing a ∆-9 tetrahydrocannabinol concentration of no more than 0.3% on a dry-weight basis. Certain standards are required for legal growing, cultivating, and producing the hemp plant. The Colorado Industrial Hemp Program registers growers of industrial hemp and samples crops to verify that the dry-weight THC concentration does not exceed 0.3%.
^ Jump up to: a b c Campos AC, Moreira FA, Gomes FV, Del Bel EA, Guimarães FS (December 2012). "Multiple mechanisms involved in the large-spectrum therapeutic potential of cannabidiol in psychiatric disorders". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences (Review). 367 (1607): 3364–78. doi:10.1098/rstb.2011.0389. PMC 3481531. PMID 23108553.