An Ohio county coroner fears the Cincinnati area has been used as a "test tube" by heroin dealers for use of a powerful animal tranquilizer.

Hamilton County's Dr. Lakshmi Sammarco (LAK'-shmee suh-MAHR'-koh) said Tuesday tests have confirmed carfentanil (kahr-FEHN'-tuh-nihl) in the bodies of eight recent overdose casualties, and more cases are suspected. The drug can be thousands of times more powerful than morphine.

She says the intense and focused spike in the area raises concerns dealers wanted to see what would happen to users of carfentanil.

Authorities say nearly 300 overdoses have been reported in the Cincinnati area beginning Aug. 19, including 174 in a six-day period and at least three deaths.

The head of the Hamilton County Drug Coalition task force wants Ohio to declare a public health emergency.