Mitragyna speciosa: see kratom.
QUESTION
Medically speaking, the term "myalgia" refers to what type of pain? See AnswerFrom 
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References
FDA. "Statement from FDA Commissioner Scott Gottlieb, M.D. on FDA advisory about deadly risks associated with kratom." Nov 17, 2017.
<https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm584970.htm>
FDA. "Statement from FDA Commissioner Scott Gottlieb, M.D., on the agency's scientific evidence on the presence of opioid compounds in kratom, underscoring its potential for abuse."
<https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm595622.htm>
<https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm584970.htm>
FDA. "Statement from FDA Commissioner Scott Gottlieb, M.D., on the agency's scientific evidence on the presence of opioid compounds in kratom, underscoring its potential for abuse."
<https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm595622.htm>