SEATTLE – Two women in King County died last month after snorting cocaine that was believed to laced with a potent, synthetic opiate that is five times stronger than heroin.

King County has since issued a warning about the acetyl fentanyl-contaminated cocaine.

"Cocaine users need to be aware that acetyl fentanyl-laced cocaine can kill quickly when snorted or injected. There is no way to know whether cocaine is laced with acetyl fentanyl, so the best prevention is to avoid use of cocaine altogether," said Dr. Jeff Duchin of Seattle-King County Public Health.

The county says acetyl fentanyl, which is not prescribed, is stronger than prescription fentanyl.

It’s believed the two women snorted and did not inject the cocaine, and that they were exposed to the same batch of tainted cocaine. Health officials are trying to find out if any other drugs were involved.

The medical examiner’s office must still confirm the cause and manner of the deaths.