In October 2016, three dogs in Broward County, Florida, showed symptoms of overdose after they assisted in a federal drug raid. The dogs were more lethargic than usual, and they refused water. In West Virginia, the Monongalia County Sheriff’s Department has also become concerned about dogs used in drug raids. Al Kisner, the department’s chief deputy, told WVNews.com that they no longer take dogs off their leads in houses that might contain fentanyl, since the dogs could chew on an object covered in the potent opioid and inadvertently overdose.

Fentanyl is 30 to 50 times more potent than heroin—so deadly that just a few inhaled grains can cause an overdose. (A few human police officers have been hospitalized after accidentally inhaling puffs of the substance.) That can be a problem when sniffing is a police dog’s primary mode of detective work, the Atlantic reports.

Fully trained police dogs are worth around $30,000 each, and police departments are looking for ways to protect these four-legged officers on the job. Colorado is equipping all of its police canine teams with Narcan, the overdose-reversal drug. Police in Canada are training dogs on liquid, rather than powder, fentanyl to minimize the risk of exposure during training. Maryland state police also carry Narcan for their dogs and are trained to look for “excessive drooling and severe limping” as symptoms of overdose. Illinois even has a law that allows for the use of ambulances to transport police dogs, if they aren’t needed for humans.