The London region’s top public health official is recommending marijuana users keep the anti-overdose medication naloxone handy.

That advice from Dr. Christopher Mackie comes after the Middlesex-London Health Unit and London police issued a public warning that fentanyl, a potentially deadly opioid, could be showing up in other street drugs, including pot.

“The more naloxone we have in our community, the safer the ­community is going to be,” Mackie, Middlesex-London’s medical officer of health, said Friday.

Thursday’s joint warning from health officials and police comes after recent urine tests from drug-users, who self-reported taking only pot or heroin, came back positive for fentanyl, an opioid up to 100 times more powerful than morphine.

The samples came from patients at the Mental Health and Addictions Crisis Centre’s suboxone clinic, said Dr. Ken Lee of Addiction Services of Thames Valley.

Participants taking suboxone, a drug therapy for opioid addiction, must get their daily dose in person and submit to a weekly drug test.

Patients eventually may be given take-home doses of suboxone after showing they’re drug-free — with an exception made for marijuana — for a period of time.

Critics of the warning that local pot could be laced with fentanyl say drug users may be motivated to lie about the substances they’ve taken, to obtain the take-home doses.

Lee acknowledged that patients lying about their drug use is a possibility, but said there’s nothing to prove it.

“The people say that when they were smoking that particular marijuana that they felt unusual, they felt sick afterwards,” Lee said of the patients whose urine showed traces of fentanyl.

“It’s not an inaccurate test.”

Reports of fentanyl-laced marijuana have popped up across North America, especially in communities ravaged by widespread opioid addiction. But there appear to be no confirmed cases of the two drugs ever being combined.

London police have yet to seize any cannabis that’s been found to contain fentanyl, but testing takes several months, so the latest results aren’t yet available, said Const. Sandasha Bough.

Still, Mackie said he doesn’t want to take chances.

In addition to doubling down on the startling warning, Mackie suggested organized crime may be adding fentanyl to pot intentionally in a bid to shift the drug market ahead of the federal government’s plan to legalize recreational marijuana by July 2018.

“I think we have enough information to be very concerned here,” Mackie said, adding extra caution should be taken with marijuana edibles.

“It would be very easy to put a little bit of fentanyl in something like that.”

Mackie urged drug users to pick up naloxone kits, which are available free of charge at the health unit, many pharmacies and community organizations.

Administered by injection or a nasal spray, naloxone can stop an opioid overdose.

dcarruthers@postmedia.com

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