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Kratom, a plant product used by some as a home remedy for opioid addiction and by others just for fun, can kill you and doesn’t belong on the market, the Food and Drug Administration said Tuesday.

The FDA says it will seize shipments of kratom and issued a public health warning telling people not to use it.

“The FDA is aware of reports of 36 deaths associated with the use of kratom-containing products,” the agency’s commissioner, Dr. Scott Gottlieb, said in a statement.

“There have been reports of kratom being laced with other opioids like hydrocodone. The use of kratom is also associated with serious side effects like seizures, liver damage and withdrawal symptoms.”

"At a time when we have hit a critical point in the opioid epidemic, the increasing use of kratom as an alternative or adjunct to opioid use is extremely concerning.”

Until it is tested like any other drug and shown to be safe and effective, Gottlieb said the FDA would work to keep marketers from selling it.

Some people think kratom is safe because it comes from a plant — it's a relative of coffee — but many poisons come from plants, including opioids, cyanide and ricin.

Related: Stop Saying Cannabis Cures Cancer, FDA Warns

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“The FDA knows people are using kratom to treat conditions like pain, anxiety and depression, which are serious medical conditions that require proper diagnosis and oversight from a licensed health care provider,” Gottlieb said.

“Importantly, evidence shows that kratom has similar effects to narcotics like opioids, and carries similar risks of abuse, addiction and in some cases, death,” Gottlieb added.

“At a time when we have hit a critical point in the opioid epidemic, the increasing use of kratom as an alternative or adjunct to opioid use is extremely concerning.”

Supporters of kratom use have been fighting to keep it legal for years. The Drug Enforcement Administration temporarily listed kratom as a Schedule 1 controlled substance last August, but withdrew the decision after an outcry and a targeted petition effort.

Dozens of web sites sell kratom, but the FDA said it would exercise its jurisdiction over the product as an unapproved drug.

“We have identified kratom products on two import alerts and we are working to actively prevent shipments of kratom from entering the U.S.,” Gottlieb said.

“At international mail facilities, the FDA has detained hundreds of shipments of kratom. We’ve used our authority to conduct seizures and to oversee the voluntary destruction of kratom products.”

Supporters say they use kratom to treat aches and pains, anxiety and to boost focus. But websites also say it can treat diabetes, addiction and acts as a sexual stimulant. Users can be very passionate about kratom.

"As a long time vendor and advocate of the kratom, we feel that adult American consumers deserve access to safe, natural, and properly labeled kratom tea products," Jeff Stratton of the website Phytoextractum said in an email.

"Kratom tea is safe when companies comply with good manufacturing practices, compliant labeling, and the scientific analysis that protects the consumer. We hope the FDA will learn from the DEA’s 2016 debacle, and reexamine all the available science and information that came to light within the last year before jeopardizing the health of countless Americans."

Gottlieb said he was sympathetic but said distributors have to show that kratom does work as advertised.

“While we remain open to the potential medicinal uses of kratom, those uses must be backed by sound science and weighed appropriately against the potential for abuse,” Gottlieb said.

“They must be put through a proper evaluative process that involves the DEA and the FDA. To those who believe in the proposed medicinal uses of kratom, I encourage you to conduct the research that will help us better understand kratom’s risk and benefit profile, so that well studied and potentially beneficial products can be considered.”

Online sellers of kratom who were contacted by NBC News did not respond immediately to a request for comment.