11 people nationwide have been hospitalized.
Kratom is native to Malaysia, where the leaves of the kratom plant are crushed to make tea, smoked, chewed, or taken as capsules.
The regulator also said it was investigating a multistate outbreak of salmonella infections linked to products reported to contain kratom.
As of February 16, the Salmonella outbreak includes 28 people in 20 states: Alabama (1), Arizona (1), California (3), Colorado (1), Florida (1), Kansas (1), Kentucky (1), Louisiana (1), MA (1), MI (1), North Carolina (2), North Dakota (1), NY (1), OH (2), Oklahoma (2), OR (2), Pennsylvania (2), SC (1), Tennessee (1), and Utah (2). In the United States, kratom items are sold as powders, pills, cases and even caffeinated drinks. Eight of 11 sick people interviewed had consumed kratom, the announcement says, leading the CDC to believe that supplies of the supplement may have been contaminated. Most people infected with salmonella develop symptoms - including diarrhea, fever and abdominal cramps - within 12 to 72 hours of exposure to the bacteria. An estimated 1.4 million cases occur in the United States each year, according to the CDC. Due to the reporting time lag, more cases of illness may be reported, the CDC said.
The U.S. Food and Drug Administration on Wednesday said it recalled and destroyed a large volume of kratom-containing dietary supplements made by a company in Missouri.
The FDA, however, has issued several warnings against the consumption of kratom.
The FDA is maintaining its stance that kratom is a drug with "serious risks", referring to it as an opioid. All agree that more research is needed.
FDA Commissioner Dr. Scott Gottlieb warned the public about the herbal supplement in a statement this month, saying that "There is no evidence to indicate that kratom is safe or effective for any medical use". The supplement can be found in head shops and gas stations.
The investigation is ongoing, the CDC said.