(NewsNation) — A large percentage of drugs from Mexican pharmacies are laced with illegal drugs such as fentanyl, heroin and methamphetamines, a University of California study found.

Pharmacies in Mexico’s border towns are starting to fill up with American customers looking for discounted medications, reports found. Some are looking for a pharmacy that doesn’t require prescriptions.

However, the UCLA-led study found that across 40 pharmacies in four cities in Mexico, “two out of three had at least one controlled substance for sale without a prescription, either in bottles or individual pills.”

The researchers bought oxycodone, Xanax and Adderall, and found that a large percentage of the pills tested positive for fentanyl, heroin and methamphetamine, suggesting they likely originated with Mexican cartels.

A Los Angeles Times investigation had similar findings. Reporters found pills being sold as oxycodone were actually fentanyl, and pills sold as Adderall tested positive for meth in Tijuana. Further south in Cabo San Lucas, even weaker painkillers tested positive for fentanyl.

“It is not possible to distinguish counterfeit medications based on appearance, because identically-appearing authentic and counterfeit versions are often sold in close geographic proximity,” the UCLA researchers wrote. “Nevertheless, US tourist drug consumers may be more trusting of controlled substances purchased directly from pharmacies.”

The LA Times investigation found that 71% of the 17 pills tested tested positive for more powerful drugs.

While these Mexican pharmacies also sell to locals, a majority of their customers are Americans traveling to find more affordable medications, the UCLA researchers reported. U.S. President Joe Biden addressed the issues of high health care costs Wednesday, vowing to reduce domestic drug prices.

The UCLA study indicates the tainted drugs found in Mexican pharmacies are escalating overdose death rates in the U.S., but it is hard to pinpoint the exact number of overdose deaths, as Mexico reports these deaths differently.

Because many of Mexico’s toxicology screenings don’t test for fentanyl, the cause of death may often be classified under a different medical issue.

“While more than 91,000 people died of overdoses in the U.S. in 2020, Mexico reported just 1,700 fatalities that year from all drugs, including alcohol,” the Los Angeles Times wrote. “Fewer than two dozen of those, according to the data, were from opioids, compared with more than 68,000 opioid overdose deaths in the U.S. that year.”

Dr. Raul Placios, a drug counselor on the Mexico side of the border, believes some of the drugs could have tested positive for meth because they contain the same active ingredient.

Another LA Times investigation says the State Department has been aware of the fake pharmaceuticals problem since 2019, but has failed to issue a warning.

While there are warnings about traveling to Mexico due to the cartel violence, two U.S. Democratic lawmakers have asked the State Department to issue better travel warnings to include warnings about counterfeit medication.