Prince May Have Known Counterfeit Drugs Contained Powerful Painkiller Fentanyl, Experts Say

Prince may have been using counterfeit drugs before his April 21 opioid overdose, according to new reports – the potency of which could have killed anyone, an expert tells PEOPLE.

At least one of the prescription pain pills found inside of an Aleve bottle at the singer's Paisley Park estate tested positive for fentanyl, a source close to the investigation told the Associated Press on the condition of anonymity. The pill was labeled "Watson 385," which typically indicates that it contained a lower-potency mix of acetaminophen and hydrocodone, a semi-synthetic opioid used for pain relief.

Although a source told the Minneapolis Star Tribune that Prince may have taken the pills – which they reported were marked as hydrocodone – not knowing they contained a more powerful drug, Ben Levenson, addiction expert and founder of Origins Behavioral Healthcare, says the mislabeling is a well-known practice in illicit prescription drug trade.

What is illegal and counterfeit fentanyl?
"[China] is now, by far and away, the number one importer of illicit – aka not made in labs approved by the FDA – fentanyl into the United States," Levenson tells PEOPLE. "They use the Mexican cartel channels, the same channels that the heroin is coming in. They're also shipping it in a very dangerous way."

The drug is cut into pill forms and cut as antibiotics, or other types of lower grade opiates, like hydrocodone or Watson 385.

"They're just trying to get it past customs, so it's coming in powder form but it's also coming in pill form," he explains. "There are statements by extremely qualified pharmacists who have said that they cannot tell the difference between a fentanyl disguised antibiotic and the actual antibiotics they would be pouring in their pharmacy."

Levenson believes that Prince likely knew that the drug he was taking was not Vicodin or morphine, but the 80-100 times more potent fentanyl, which is mostly only used by doctors in the operating room.

"Opiates create what's called tolerance and withdrawal," he says. "His tolerance levels for fentanyl were probably through the roof. If you or I took a [Watson 385] that was really fentanyl, it would kill us. It's a great way to disguise it and get it into the country, and also keep it in your house if your house gets searched."

He further contends, "If they were indeed [Watson 385s], and came from our National Drug Supply, it would be chaos – they'd be shutting down the whole system... He didn't get hydrocodone disguised as fentanyl at Walgreens."

Nearly two dozen prescription narcotic pills were found in a bottle of the over-the-counter medicine Aleve in the 57-year-old's home, the source told the AP. The "Purple Rain" singer had no prescription for any controlled substance in the state in the year before he died, the source told the AP, adding that authorities are working to determine how Prince obtained the drugs.

"The investigation of Prince's death remains open and active. Our office is not able to provide any details about the specifics of the investigation at this time," the Carver County Sheriff's Office told PEOPLE Monday morning.

Hydrocodone vs fentanyl
The difference between hydrocodone and fentanyl is significant, Dr. Joseph Garbely, Medical Director at Caron Treatment Centers, tells PEOPLE.

"Hydrocodone is very commonly used and it's much weaker [than fentanyl]," he says, "It's actually weaker than morphine. You have one that's much more potent than morphine and one that's significantly less potent than morphine. So if you mix them up, you are getting something much stronger than you anticipated."

Garbely and Leveson call fentanyl a growing problem in America, and say it is often mixed with heroin before being sold on the street.

"[This year], we had 3,383 overdose deaths in Pennsylvania, overdose deaths – 55 percent were heroin related and then 26 percent were fentanyl," Garbely says. "So you can see that it's becoming a big problem."

Garbely adds, "Dealers know what they have and they're mixing it in. They know that fentanyl is stronger than heroin... it's one of the most potent opioids on the planet. They relish the chance of mixing it into heroin because they know there will be an uptick in their business because of that."

Dr. David Sack, addiction psychiatrist and CEO of Promises Treatment Centers, also tells PEOPLE that fentanyl is easy to manufacture in large batches because it is entirely synthetic.

"Fentanyl has an extremely fast onset and a fast offset compared to something like heroin," Levenson explains. "Heroin has a slower onset, and so they have a longer period of time before they go into respiratory arrest... and so with heroin, you'd have maybe a 20 minute period, but with fentanyl, the problem is that you have from zero to about three minutes until they are in full respiratory arrest."

WATCH: Fentanyl: 5 Things to Know About the Drug That's Connected to Prince's Death

What is U-47700?
Some of the pills reportedly found in Prince's stash contained fentanyl, lidocaine and U-47700, which is another synthetic opiate that was never introduced or used clinically, Sack says.

U-47700 bonds to the body's kappa-opiate receptor, which can cause hallucinations, according to Sack. "We think that people might be taking it because, in addition to euphoria, they're getting this sense of disassociation and unreality and hallucinations," he says. "Which, if you're a young kid looking to get high, may be attractive to you. The reality is that it also causes intense fear and anxiety because the same receptors control a range of emotional responses. So it's bad news on a lot of levels."

Sack says the drug is somewhat deceptive at low dosages, though, especially when users are mixing it with other drugs.

"They don't know they're not taking Vicodin or oxycodone, so their ability to judge how much to take is really reduced," he says, "And that's one of the dangers of counterfeit and substituted drugs. Even if it's working on the same receptors, the potency can be very different."

Further, the combination of U-47700 with fentanyl and lidocaine, a local anesthetic, can cause irregular heartbeat, he says.

"If someone has other heart irregularities, it could be a problem," Sack explains. "The real problem is the fentanyl with the oxycodone or the hydrocodone, because then you start to get serious complications. Because each one of them can independently can suppress respiration."

He continues, "When you put them together, your likelihood of having a respiratory arrest-type overdose goes way, way up. And that very well may have been what happened to Prince. He may have been able to manage the drugs individually, but the combination or the substitution might have compromised."

• With reporting by JORDAN RUNTAUGH