Massachusetts U.S. Sen. Ed Markey is asking two national organizations that deal with life insurance for details about companies that deny coverage to applicants who carry naloxone, often sold as Narcan, the drug that reverses an opioid overdose.

Markey's letter comes in response to a WBUR story last week about a nurse at Boston Medical Center who was denied coverage from two different insurers because she carries naloxone. She's reapplied for coverage with the second insurer.

"I am concerned that if [G]ood Samaritans are denied insurance coverage because they carry naloxone to promote public health and safety, this will have a chilling effect on efforts to make naloxone widely available and accessible, and will ultimately cost lives," Markey said in a letter Monday to the National Association of Insurance Commissioners (NAIC) and the American Council of Life Insurers (ACLI).

The letter includes a number of questions: How do insurers determine if an applicant is prescribed naloxone because they are at risk for an overdose, or to save others; how often have applicants been denied life insurance for carrying naloxone; and whether there are guidelines to prevent wrongful denials.

The letter also asks whether life insurers are aware that most states have issued what's known as a standing order for naloxone, meaning one prescription that works for anyone who wants to buy naloxone at their local pharmacy.

Dr. Alex Walley, the Boston-based physician who signs that order for everyone in Massachusetts, has been asked to write letters for about half a dozen life insurance applicants explaining why they carry naloxone. He says he can't answer whether the applicants do or do not use drugs.

"I can't do that, they're not my patients, I haven't examined them, I don't know their status," Walley said. "I think in a lot of a cases the insurance companies don't exactly understand the situation, they're not plugged into state policy and what a pharmacy standing order is."

The NAIC says it does not know of any cases in which an applicant was denied life insurance because they carry naloxone. Both the NAIC and the ACLI said they had received the letter and will review it.

In April, U.S. Surgeon General Dr. Jerome Adams issued a national call for everyone who knows someone at risk for an opioid overdose to carry naloxone.

"The science tells us that naloxone saves lives, and it is important that all Americans know about the vital role bystanders can play in preventing opioid overdose deaths when equipped with this life-saving medication,” Adams said.