BOSTON — A group of U.S. senators has asked the Drug Enforcement Administration to clarify the rules concerning the partial filling of prescriptions for opioids and other drugs as states like Massachusetts consider policies to limit the quantity of painkillers being dispensed as a tool to fight addiction.

U.S. Sen. Elizabeth Warren and four other senators, including U.S. Sen. Edward Markey, sent a letter to the DEA on Tuesday requesting guidance or the development of a new rule to make clear to states that the partial filling of prescriptions for Schedule II drugs is permitted under federal law.

“These ‘partial-fill’ policies could empower patients to work with their doctor and pharmacist to achieve the desired level of pain control while also limiting the amount of unused medication in their home,” the letter stated.

In addition to Warren and Markey, the letter was signed by Connecticut Sen. Richard Blumenthal, a Democrat, and Republican Sens. Kelly Ayotte, of New Hampshire, and Shelley Moore Capito, of West Virginia.

In Massachusetts, the state Senate earlier this year approved an opioid-abuse prevention bill that included a provision pushed by Quincy Sen. John Keenan to allow for the partial filling of opioid prescriptions. The measure passed after debate over whether the policy would run afoul of federal law.

The original bill proposed to allow individuals to take out their prescriptions for schedule II narcotics, which includes drugs like Oxycontin, in smaller batches over time, but still adding up to the total prescription size. That section was ultimately amended in an attempt to comport with federal law to allow a one-time smaller fill at the patient’s request, but would require the patient to go back to their doctor in order to receive the balance of the prescription.

According to the letter sent to the DEA by Warren and others, the Controlled Substances Act and the Food Drug and Cosmetic Act don’t speak to the partial filling of prescriptions, while current DEA regulations stipulate that pharmacists can partially fill prescriptions for Schedule III, IV and V substances, but Schedule II drugs, which include opioids, can only be partially filled in a long-term care setting for terminally ill patients when inadequate supply prevents the full filling of the prescription.

“While these regulations do not specifically prohibit partially filling prescriptions for Schedule II substances in other scenarios, the lack of clarity has deterred states from moving forward with partial fill policies,” the senators wrote.

Over 70 percent of adults who misuse prescription opioids get the drugs from friends or relatives through unused prescriptions, according to the letter that cites the National Institute on Drug Abuse.

Gov. Charlie Baker, in his opioid-abuse prevention bill, took a different approach to curbing the amount of drugs being dispensed by proposing to limit doctors to prescribing no more than a 72-hour supply of opioids at one time to new patients.

At a hearing on partial fills legislation in July, Keenan said patients are sometimes hesitant to discuss prescription quantities with their physicians, and said patients are often told that since they are paying the full co-payment they should fill the full prescription because “if you need it, you’ll have it.”

The trade group representing 17 insurance companies, the Massachusetts Association of Health Plans (MAHP), opposed the partial fills bill in July, noting the legislation didn’t require pharmacists to notify insurers or their pharmacy benefits managers about partially filled prescriptions.

“This could create confusion as to why the prescription differs from the quantity filled, as well as concerns about the appropriateness of the decision to overrule the medical judgment of the prescriber based on limited information provided at the time the prescription is filled,” MAHP wrote in its testimony to lawmakers.

The senators asked the DEA to respond by Jan. 31.

The DEA is run by Acting Administrator Chuck Rosenberg. According to his bio, Rosenberg has worked as chief of staff to FBI Director James Comey, was a partner at a Washington D.C. law firm, and served as the U.S. Attorney for both the Eastern District of Virginia and the Southern District of Texas. Rosenberg is a graduate of Tufts University, Harvard University, and the University of Virginia School of Law.