Late in 2015, a group of San Francisco friends took what they thought was the anti-anxiety medication, Xanax. Within 48 hours, three of them were dead due to overdoses of the powerful end-stage cancer painkiller, fentanyl.

Three residents of San Francisco have died as a result of taking counterfeit Xanax, according to KRON4 local news report from October of last year. The report followed a warning from the San Francisco Health Department linking overdose cases to fake Xanax pills laced with fentanyl that had been found by the department.

The original news reports from CBS stated that SF resident Andrea Choye was found dead in her home after paramedics were called to the residence to assist three others who were suffering symptoms of overdose. Two of those three have subsequently died.

SF Health Department Medical Examiner, Doctor Phillip Coffin told KPIX news that “The front and the back look almost identical to a real Xanax pill. It’s extremely hard to distinguish them.” He also state that he found the counterfeiting of Xanax “particularly concerning to me because it involves a pill, Xanax, that is commonly bought by people who are looking to, say, calm down from a night of partying.”

A report in Tech Times notes that several Pinole Valley High School students have also been hospitalized as a result of taking what may have been fake Xanax.