The Drug Enforcement Administration (DEA) has added another fentanyl-related drug, known as furanyl fentanyl, to its list of banned substances, according to The Wall Street Journal.

Furanyl fentanyl started appearing in a national database that tracks drug seizures in December 2015, the article notes. The drug has been linked with 325 deaths through October of this year.

The legal form of fentanyl, which is used to help cancer patients manage serious pain, is up to 50 times stronger than heroin. Illegal versions of the drug are often made in China and mixed into heroin or added to fake prescription pills.

Last month the DEA temporarily banned the synthetic drug Pink under federal law. The agency has received reports of at least 46 confirmed deaths associated with the drug, also known as U-47700.