SSRIs inhibit this enzyme, so the researchers hypothesized that patients taking SSRIs in combination with prodrug opioids would receive less pain relief. Prodrug opioids include codeine and hydrocodone, which is sold under brand names such as Vicodin, Lorcet and Lortab. SSRIs include Prozac, Paxil, Zoloft and Celexa.

For the study, the research team analyzed de-identified data for 4,306 surgical patients with a diagnosis or symptoms of depression in the electronic health records at Stanford Health Care.

The researchers found that the patients on SSRIs who were prescribed prodrug opioids experienced more pain when they left the hospital, as well as three weeks later and eight weeks later. The patients on both SSRIs and prodrug opioids registered nearly one point more pain on a scale of 1 to 10 than the patients not on SSRIs who were prescribed prodrug opioids.

Algorithm predicts opioid response

The researchers built a machine-learning algorithm that predicts how a patient will respond to different types of opioids. The algorithm is available online.

The study focused on surgery patients because they nearly always receive opioid prescriptions, yet the findings apply to anyone taking short-term opioids.

Carroll noted that hydrocodone is the most frequently prescribed drug in the nation. With SSRIs the most frequently prescribed class of drugs, he said, the chance that any patient will be on both drugs is high.

There’s no proof that better pain management reduces the number of opioid overdoses, cautioned Carroll. But poor pain control has been shown to be a risk factor for chronic pain, and it may lead to more prolonged opioid use, along with misuse.

“Presumably, every day you take opioids, the risk you’ll abuse it increases,” Carroll said.

Depressed patients are at greater risk for pain, and we’re failing them because we’re not educated enough about the drugs we’re giving them.

The authors concluded that to manage pain for patients on SSRIs, prescribers should choose nonopioids or direct-acting opioids. Direct-acting opioids, which include morphine, fentanyl and oxycodone, do not need the liver enzyme to convert the drug into a form that eases pain.

Prescribers typically choose hydrocodone or codeine because of a perception that they are milder than hydromorphone, whose trade names include Dilaudid and Exalgo, or morphine, Carroll said.

“The prescribing of hydrocodone has more to do with history and perception,” he said. “The liver converts hydrocodone into hydromorphone and converts codeine into morphine,so the result is the same.”

Carroll added that depressed patients’ complaints about pain after receiving opioids are often dismissed because of their mental state, when the problem lies in an unfortunate drug interaction.

“Depressed patients are at greater risk for pain, and we’re failing them because we’re not educated enough about the drugs we’re giving them,” he said.

Hernandez-Boussard is a member of Stanford Bio-X, and she and Carroll are members of the Stanford Cancer Institute.

Other Stanford co-authors of the study are research scientist Imon Banerjee, PhD; Keith Humphreys, PhD, professor of psychiatry and behavioral sciences and the Esther Ting Memorial Professor; Steven Asch, MD, MPH, professor of medicine; and Catherine Curtin, MD, associate professor of surgery.

The work was funded by the Agency for Health Care Research and Quality.

Stanford’s departments of Medicine, of Biomedical Data Science, of Surgery and of Anesthesiology, Perioperative and Pain Medicine also supported the work.