All pharmacies are regulated by the state where they are located, but regulations vary state by state, Outterson said.

The FDA has tried to oversee these pharmacies, but the attempt failed. The FDA developed rules for compounding but litigation led to a U.S. Supreme Court ruling in 2002 that struck down the idea, Outterson said.

Congress has been unable to reestablish the FDA's authority over the pharmacies since.

What are officials doing about the outbreak?

The FDA, the CDC and the Massachusetts Board of Registration in Pharmacy are all investigating the outbreak.