Illicitly bought prescription drugs have killed more than a dozen people in California who were expecting something much weaker. A CDC report released Tuesday warns that hospitals in the Bay Area have recently treated at least seven patients who overdosed after taking what they thought was Norco, a medium-strength opioid painkiller.

The pills actually contained fentanyl, a far more powerful drug that's 100 times more potent than morphine, according to the CDC. The Bay Area patients survived, but Sacramento County officials have reported 12 deaths linked to fake Norco in recent weeks, with another two fatal overdoses in neighboring Yolo County.

Health officials obtained one of the fake pills from a Bay Area patient and discovered that it was an exact replica of a Norco pill, Medical Daily reports.

Finding the source of the fakes "is our number one priority based out of San Francisco," a DEA special agent in the city tells the AP.

"We definitely want to connect the dots where we can." The CDC report says fake medicine containing fentanyl is an "emerging and serious public health threat" and that it's vital for the general public to realize the "significant risks to life and health when purchasing what appears to be prescription medications from any source other than a reputable pharmacy or health care provider." (Experts are very worried about a new street drug that's 100 times more powerful than fentanyl—and still legal.)

This article originally appeared on Newser: These Look Like a Popular Painkiller. 14 Who Took Them Are Dead

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