United Nations officials this week voted to bolster regulations of four chemicals contributing to the growing opioid crisis in the U.S. and elsewhere.

The Wall Street Journal reports that steps taken by the UN Commission on Narcotic Drugs would add the chemicals to lists of controlled substances maintained by UN conventions.

Two of the chemicals, known as ANPP and NPP, are commonly used to make illicit fentanyl, a painkiller far more potent than heroin that is linked to thousands of overdose deaths in the U.S.

The Journal, which previously reported that lax trade regulations allowed Chinese firms and Mexican traffickers to smuggle counterfeit fentanyl into the U.S., said that the UN vote requires companies to monitor exports, inform other countries of shipments and seize chemicals linked to illicit narcotic production.

The other two substances added to UN lists — butyrfentanyl and U-47700 — are compounds that mimic fentanyl.

Former Secretary of State John Kerry and 15 U.S. senators previously urged the UN to crack down on shipments of opioid chemicals.

The Department of Health and Human Services said that the rate of overdose deaths involving opioids nearly quadrupled since 1999 and that deaths involving heroin or synthetic opioids — including fentanyl — sharply increased of late.