Two recent deaths in Western Pennsylvania prompted state health officials on Tuesday to issue a stern warning about a particularly deadly opioid.

Carfentanil, a synthetic drug that is exponentially stronger than morphine, is used legally to sedate elephants. In late December, two residents of Beaver County, northwest of Pittsburgh, fatally overdosed after using heroin laced with the substance.

"Carfentanil is intended to sedate large animals and is not meant for humans," state health secretary Karen Murphy said in a statement. "It can potentially kill anyone who comes into contact with it."

An amount of carfentanil as small as a grain of sand can be fatal. Murphy advised emergency responders to use extra caution when treating known or suspected carfentanil overdoses.  Victims often need several doses of the overdose-reversal medication naloxone to be revived.

More than 3,500 Pennsylvanians died from a drug overdose in 2015, according to state data. Overdoses of opioids, a category that includes prescription pain relievers as well as heroin and fentanyl, are the leading cause of accidental death in the state.

In Philadelphia last year, about 900 people died of a drug overdose, according to the city Medical Examiner's Office — triple the number of homicides.