Health insurer Cigna is lowering the out-of-pocket cost of insulin for some of its members with diabetes, launching a new program next year that caps copays at $25 for a 30-day supply of the drug.

The insurer said the program could lower costs for roughly 700,000 members with diabetes covered under Cigna plans and its pharmacy benefits subsidiary Express Scripts. The average cost for a 30-day supply of insulin was previously $41.50, Cigna said.

The program is being offered as part of nongovernment Cigna plans for employers, unions and individuals. Employers and other groups have the option of adopting the $25 copay at any time, it said. It is not now available for Cigna-administered Medicare and Medicaid government plans.

"We are confident that our new program will remove cost as a barrier for people in participating plans who need insulin," said Dr. Steve Miller, Cigna executive vice president and chief clinical officer, in a statement announcing the program Wednesday. "We need to ensure these individuals feel secure in their ability to afford every fill so they don't miss one dose, which can be dangerous for their health."

Rising insulin prices have been a focal point in the debate over high drug costs. Earlier this year, witnesses testified during drug hearings in the U.S. House and the Senate about how high costs had forced loved ones to ration their insulin intake with life-threatening impacts on their health.

Cigna said more than 25 percent of the 24 million Americans diagnosed with diabetes use insulin to keep their blood glucose levels healthy. It cited a Yale study that found that one in four people who use insulin have cut back on the drug because they can't afford it.

The Senate Finance Committee has launched an investigation into insulin prices and called on the nation's largest insulin producers to testify on Capitol Hill.

Sen. Chuck Grassley, chairman of the committee, said in a statement Wednesday that it's good news for patients any time out-of-pocket drug costs are lowered but questioned why Cigna's cost-cutting is only happening now.

"Why couldn't this have been done years ago?" Grassley asked. "It shouldn't take bad press and congressional scrutiny to get health plans, their pharmacy benefit managers and pharmaceutical companies to arrive at a fair price for a drug that's been on the market for nearly a century."

Last month, Eli Lilly, the nation's largest producer of insulin, introduced a generic version of its rapid-acting insulin product for half the price of its flagship Humalog product.

Cigna's move comes one week before Miller and four other pharmacy benefit management executives are scheduled to testify about the role of PBM contracts in drug price increases.

President Donald Trump's administration has proposed banning the confidential discount agreements on Medicare plans. The comment rule on that proposal ends on April 8, and the administration is expected to issue the final rule sometime this spring.

Correction: An earlier version of this story said the copay program is starting now. Express Scripts later clarified that it is being offered now for plans that want to adopt the program for 2020.