Endo International PLC said Thursday that it had sold back the rights to an opioid pain drug to BioDelivery Sciences International Inc., as the market for opioid-based painkillers has come under fire.

Regulators and experts say the overuse of opioid-based pain treatments has contributed to an opioid epidemic. Earlier this year, the Centers for Disease Control and Prevention released long-awaited guidelines limiting the prescribing of opioid painkillers.

On Thursday, Endo said it was selling back the rights to the drug as the opioid market had evolved, and that it wanted to focus on drugs that didn't require a sales force. In November, Endo said it was evaluating how to maximize the value of the drug in a "challenging opioid market."

The drug, belbuca, delivers the low-level opioid buprenorphine through a dissolvable film placed in a patients' cheeks and is meant for treating long-term chronic pain. BioDelivery said its drug is a "responsible solution" for treating chronic pain while also being "differentiated" from other opioids to help prevent abuse. Buprenorphine is classified by regulators as a schedule III controlled substance, meaning regulators say it has a lower abuse potential than schedule II drugs. Many commonly given opioids are schedule II.

Last month, BioDelivery said belbuca "sales continue to demonstrate the potential for growth, despite the current challenges around the use of opioids to treat pain." In August, Endo said it planned to increase its marketing investment in belbuca.

Endo said Thursday it had reached an agreement to return the rights to belbuca to BioDelivery. Endo had been responsible for developing and commercializing the drug since 2012. The companies won't have any future royalty or milestone payments to each other. Endo will lay off its 375-member sales force for the drug and would take a $40 million write-down and other costs of $22 million. It also expects $90 million to $100 million in cost savings.

BioDelivery said the drug is on track for $27 million in annual sales. The company also said it would now focus on selling the pain-treatment drug instead of trying to increase sales of its opioid-addiction treatment drug, citing the larger pain market and the larger amount of revenue generated per patient.

Shares of BioDelivery rose 2.9% in premarket trading as shares of Endo rose 0.2%.

Write to Austen Hufford at austen.hufford@wsj.com

(END) Dow Jones Newswires

December 08, 2016 10:15 ET (15:15 GMT)

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