By Deena Beasley

(Reuters) - Amid a growing U.S. opioid addiction, health insurer Cigna Corp will stop covering OxyContin, the opioid painkiller sold by Purdue Pharma LP, as of Jan. 1 and will instead cover an equivalent with a formulation less vulnerable to abuse, the company said on Wednesday.

The insurer has signed a "value-based contract" with Collegium Pharmaceutical Inc for Xtampza ER, an extended-release oxycodone equivalent that cannot be made more fast-acting through cutting or crushing.

Under the contract, Collegium will reduce the cost of the medication for many of Cigna's benefit plans. Cigna said the contract makes the drug maker "financially accountable" if prescriptions exceed a specific daily dose threshold. The company did not immediately respond to requests for details.

Cigna said it believes that linking financial terms to dosage may encourage more education to prevent overprescribing.

According to the U.S. Centers for Disease Control and Prevention, opioids were involved in over 33,000 deaths in 2015, the latest year for which data is available, and the death rate has continued rising, according to estimates.

Purdue Pharma has been sued by several states and local governments who accuse the OxyContin maker of deceptive marketing practices that have contributed to a national opioid addiction epidemic.

Cigna is notifying customers with current OxyContin prescriptions and their doctors of the upcoming change, but individuals who have started using OxyContin for hospice care or cancer treatments will continue to have the medication covered in 2018.

The insurer said it will consider approving coverage for OxyContin if a doctor feels the drug is medically necessary.

(Reporting By Deena Beasley; Editing by Cynthia Osterman)