Recreational and religious cannabis use goes back literally thousands of years. Charred seeds have been found in a ritual brazier in Romania, at a burial site dated to the third millennium BC. At about the same time (roughly 2700 BC), the Chinese medical encyclopedia Pen Ts’ao, compiled by emperor Shen-Nung, referred to ma (the Chinese name for cannabis) as a medicine that uniquely balanced yin and yang forces. The drug was recommended for treating menstrual cramps, gout, rheumatism, malaria, and (ironically enough, given that modern medical science considers marijuana use a potential source of permanent memory damage) absentmindedness. In the early second century, Chinese doctor Hua T’o used cannabis as a surgical anesthetic. The drug got considerably less respect in mid-twentieth-century America, where it became associated with teenage rebellion and getting high for the fun of it. Use was illegal throughout the United States until 1996, when California approved marijuana for use in medicine. Currently, twenty-nine states and the District of Columbia allow some level of legal use; as of late 2017, however, the drug remains a Schedule I substance (no recognized medical use) under federal law. The FDA does recognize two cannabis-derived nausea medications, dronabinol and nabilone.