Health insurance companies may not impose an “arbitrary limit” on coverage for naloxone, a drug used to treat narcotic overdoses, the Department of Financial Services said in a letter to insurers Sept. 28.

In the letter to insurers, the state agency said that naloxone—which blocks or reverses the effects of opioid medications such as oxycodone and fentanyl—must be covered by insurers when medically necessary.

“Insurers may not impose any arbitrary limits on coverage for naloxone, for example, issuers may not place an annual limit on coverage for an unused naloxone prescription refill (as some issuers may be doing) unless medically warranted,” wrote Lisette Johnson, the bureau chief for DFS's health bureau.