(NewsNation) — Police departments across the country have recently warned of finding marijuana laced with fentanyl, but one doctor is cautioning not to put too much stock in the warnings.

Concerns over fentanyl have grown as more drugs are being laced with the deadly narcotic. Authorities in states including Alabama, Illinois, Louisiana and New York all claimed to have begun finding fentanyl-laced marijuana.

In one of the most recent cases, the district attorney in Montgomery County, Pennsylvania, just outside Philadelphia, said Friday that police discovered THC gummies that contained fentanyl and claimed the supposedly tainted product was responsible for two overdoses.

But the office walked that back Monday, saying testing conducted over the weekend found that the products “did not alert to any illegal drugs at the lab’s threshold level of detection.”

One doctor who argues the reports should be taken with a grain of salt is Dr. Ryan Marino, a toxicologist who has conducted extensive research on fentanyl exposure.

“Not to say that it’s not possible for someone to maliciously put it in there, there are bad people out there, but we’re not seeing that,” Marino said Tuesday on “CUOMO.” “Despite all those reports, there’s never been a confirmed case where it ended up being real.”

Fentanyl is a synthetic opioid that is cheap to produce and frequently cut into other drugs to increase a dealer’s bottom line. Because of its intensity, users can get a stronger high on less product.

But it’s also extremely lethal. The Drug Enforcement Administration says it takes just 2 milligrams for someone to overdose. The agency seized more than 50 million fentanyl pills last year and has already intercepted more than 4.5 million this year.

“It is both scientifically and economically preposterous in addition to being illogical,” for someone to cut fentanyl into marijuana, Marino tweeted earlier this week. “Thanks to laws of chemistry and physics, we can know better.”

He explained that even if fentanyl were in a marijuana plant, it begins to break down into its separate compounds at temperatures higher than 350 degrees Celsius, less than that of the flame from a lighter, which burns at around 2,000 degrees Celsius. Once the fentanyl does burn off, it releases irritants that can cause lung injury.

Put those together, Marino says, and you get a scenario that would make smoking marijuana unpleasant.

“When it comes to cannabis … to my knowledge, there’s never been a good, verifiable claim of marijuana testing positive for fentanyl using validated testing methods.”

In the Montgomery County case, police said they used an IONSCAN 600 device, which is capable of detecting “trace amounts of explosives and narcotics,” according to the manufacturer’s website.

So how might law enforcement come to the conclusion that fentanyl is in marijuana?

Cross-contamination is one possibility. If fentanyl and marijuana are being produced in the same area, trace amounts of the opioid could end up in the cannabis.

Marino acknowledges that fentanyl is a major problem, but one of his main goals is to dispel myths about the drug.

“What people need to know is where (fentanyl) is and what to do about it,” Marino said. “This is something we should be talking about.”