Nearly 30 percent of U.S. patients prescribed opioids by doctors over the course of a decade had no recorded pain diagnosis, according to a new letter published in the Annals of Internal Medicine.

Researchers analyzed data from 31,943 visits in which a patient age 18 or older received an opioid prescription, part of the National Ambulatory Medical Care Survey. The Centers for Disease Control and Prevention conducts this annual survey to track why people visit physician offices, what diagnoses, services and treatments they receive, and what medications are prescribed.

“In too many cases, addiction still starts with a prescriber’s pen.”

Of all visits between 2006 and 2015 (the latest available when this research began), two-thirds of patients who were prescribed opioids to treat doctor-diagnosed pain, and an additional 5 percent of patients received opioids for cancer-related pain. But in the remaining visits — 28.5 percent — physicians did not record any pain to support the opioid prescription.

The research team did not make a conclusion that these prescriptions were inappropriate, said Tisamarie Sherry, an associate physician at Brigham and Women’s Hospital in Boston and the letter’s lead author. There was not enough information to make that judgment, Sherry said.

For roughly one out of three patients already prescribed opioids, there was no recorded pain diagnosis to justify why they received at least one refill of their existing opioid medication. This is many more people than the one out of five patients who received new prescriptions for opioids. which suggests more people refilled prescriptions without justification than got new prescriptions.

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In many cases, physicians prescribed opioids without a clear understanding of how addictive those medications were. Greater awareness of this riskin recent years, along with a nationwide prescription drug monitoring program that flags doctor-shopping, has led to decreased opioid prescriptions. But the work isn’t finished.

“In too many cases, addiction still starts with a prescriber’s pen, either directly or indirectly through prescription drugs left over, and acquired or stolen from friends or family members,” Food and Drug Administration Commissioner Scott Gottlieb said during a speech in April.

In 2012 alone, doctors wrote 259 million prescriptions for opioids, the CDC said, “enough for every adult in the United States to have a bottle of pills.”

In March 2016, the CDC issued physician guidance on opioid prescription, which definitively addressed when chronic pain required opioids and how to manage that prescription once it began; how to select, dose and discontinue opioids; and how to weigh the risks and benefits of prescribing opioids in the first place.

Patients with complicated, chronic illness may require a more nuanced treatment approach beyond reflexively prescribing (or denying) opioids.

During a September 2016 Poynter Institute seminar on opioids in the U.S., Dr. Debra Houry, who directs the CDC’s National Center for Injury Prevention and Control, said the United States would reverse skyrocketing rates of opioid misuse and overdose, “if we can stop the tide of people getting addicted in the first place” and find “better alternatives.”

Since then, policymakers and the public have pressured the medical community to adopt more conservative practices in prescribing opioids. In November, the Trump administration’s opioid commission issued 56 recommendations for ways the nation could make progress in the opioid crisis.

Still, an estimated 72,000 Americans died in 2017 as a result of drug overdose, according the latest preliminary federal data, eclipsing the previous year. More than 49,000 deaths involved opioids — marking a 4.1-fold increase since 2002. Of those deaths, prescription opioids contributed to more than 19,300 fatal overdoses. This public health crisis is also contributing to a drop in U.S. life expectancy, according to federal data released in December.

While the data used in this latest research came before the CDC published its guidelines, Nicole Maestas, an associate professor of health care policy at Harvard Medical School and the letter’s co-author, said her team’s research “shines a light on this issue.”

Even when armed with greater insight into the past, the medical community doesn’t necessarily have easy answers to pressing questions around opioid use and its potential dangers. Patients with complicated, chronic illness may require a more nuanced treatment approach beyond reflexively prescribing (or denying) opioids, and doctors are “going to deal with these much harder questions,” Maestas said.