The US State Department has issued a travel warning about dangerous counterfeit pills being sold at pharmacies in Mexico that often contain fentanyl.
The travel alert posted Friday says Americans should "exercise caution when purchasing medication in Mexico."
Small pharmacies in tourist areas and border regions sometimes sell medications advertised as OxyContin, Percocet, Xanax and others without a prescription.
The State Department warned that such pills are often counterfeit and "may contain deadly doses of fentanyl."
"Counterfeit pills are readily advertised on social media and can be purchased at small, non-chain pharmacies in Mexico along the border and in tourist areas," it said.
READ | Amid US pressure on fentanyl, Mexico raises drug lab raids data
A study led by researchers at the University of California, Los Angeles found that 68% of the 40 Mexican pharmacies visited in four northern Mexico cities sold Oxycodone, Xanax or Adderall, and that 27% of those pharmacies were selling fake pills.
UCLA said the study, published in January, found that "brick and mortar pharmacies in Northern Mexican tourist towns are selling counterfeit pills containing fentanyl, heroin, and methamphetamine. These pills are sold mainly to US tourists, and are often passed off as controlled substances such as Oxycodone, Percocet, and Adderall."
"These counterfeit pills represent a serious overdose risk to buyers who think they are getting a known quantity of a weaker drug," said Chelsea Shover, assistant professor-in-residence of medicine at the David Geffen School of Medicine at UCLA.
Anecdotal evidence suggest that the problem exists in beach resorts like Playa del Carmen and Tulum, not just in border cities.
The State Department did not respond to a request for comment on whether any Americans had overdosed or died due to the Mexico drug sales.
A State Department spokesperson wrote in response to the request that "The US Department of State has no higher priority than the safety and security of US citizens overseas. We take seriously our commitment to provide US citizens with clear, timely, and reliable information about every country in the world so they can make informed travel decisions."
READ | More fentanyl enters the US and Canada than Mexico, says Mexican president