Feb. 16, 2018 -- The FDA on Friday warned pet owners that several popular brands of dog food has been found to include small amounts of a drug used to euthanize animals.

The agency says it is investigating how pentobarbital wound up in certain shipments of Gravy Train, Kibbles 'N Bits, Ol’ Roy, and Skippy canned wet dog food.

"The FDA’s preliminary evaluation of the testing results of Gravy Train samples indicates that the low level of pentobarbital present in the withdrawn products is unlikely to pose a health risk to pets," the agency says in its advisory. "However, pentobarbital should never be present in pet food and products containing any amount of pentobarbital are considered to be adulterated."

J.M. Smucker Co., owner of the brands in question, said it has pulled specific shipments of Gravy Train, Kibbles 'N Bits, Ol’ Roy, and Skippy canned wet dog food.

The move, which is not considered an official recall, came after a Washington, D.C., television station said it had several varieties of dog food tested in an independent lab. Those results, WJLA said, found several products that tested positive for pentobarbital. Pentobarbital is a barbiturate drug that is most commonly used in animals as a sedative, anesthetic, or for euthanasia, the FDA says.

An agency spokeswoman told WebMD on Wednesday that the FDA is "thoroughly reviewing" the state's results and that the "agency will determine appropriate action."

“Veterinarians and animal nutrition specialists, as well as the FDA, have confirmed that extremely low levels of pentobarbital, like the levels reported to be in select shipments, do not pose a threat to pet safety,” J.M. Smucker Co. spokesman Ray Hancart told WebMD in a statement. “However, the presence of this substance at any level is not acceptable to us and not up to our quality standards. We sincerely apologize for the concern this has caused.”

Hancart says customers with questions or concerns can call 800-828-9980 or email the company through its website.

Hancart says the company continues to investigate and is “extremely disappointed that pentobarbital was introduced to our supply chain.”