The Food and Drug Administration (FDA) is warning that the supplement known as "kratom" is an opioid and has been linked with 44 deaths, The Washington Post reports. Kratom, an unregulated botanical substance, is used by some people to relieve pain, anxiety and depression, as well as symptoms of opioid withdrawal. The FDA recently conducted a scientific analysis that provided even stronger evidence of kratom's opioid properties, the agency said in a statement. "We have been especially concerned about the use of kratom to treat opioid withdrawal symptoms, as there is no reliable evidence to support the use of kratom as a treatment for opioid use disorder and significant safety issues exist," said FDA Commissioner Scott Gottlieb. The analysis has "contributed to the FDA's concerns about kratom's potential for abuse, addiction, and serious health consequences; including death."