More than 2 million people in the United States are dependent on prescription opioid pain relievers, a number that continues to grow as the rate of opioid prescriptions has skyrocketed in the past 25 years.

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Opioids are an effective post-surgery pain management option, but they come with a risk.

About 6 percent of patients who take opioids for the first time to relieve pain after surgery end up taking the medications for far longer than is clinically recommended, a University of Michigan study found earlier this year.

And a new study from U-M shows that for patients with cancer, the news is worse.

More than 10 percent of people who had never taken opioids prior to curative-intent surgery for cancer continued to take the drugs three to six months later, according to the study, published in the Journal of Clinical Oncology. The risk is even greater for those who are treated with chemotherapy after surgery.

"We wanted to look at patients who had potentially curable disease, such as early stage breast cancer, colon cancer or melanoma," says lead study author Jay Lee, M.D., a general surgery resident at Michigan Medicine. "These patients deserve special attention, because if they're going to be free from cancer, we'd also like them not to be on opioids long term."

Why cancer patients?

Several factors can make cancer patients more vulnerable to opioid misuse, says Lee, including the emotional trauma of a cancer diagnosis, pain from invasive procedures and a large care team that may not be coordinating prescriptions.

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"Cancer pain is challenging to treat, and opioids are a crucial part of the treatment plan for those patients," says Lee. "Because of this, patients with cancer have been relatively protected from recent efforts to reduce opioid prescribing. Unfortunately, we don't understand the potential risks of opioids for patients with cancer."

Researchers used a national data set of insurance claims to identify 39,877 cancer patients who had never previously used opioids and were prescribed the drugs after undergoing curative-intent surgery from 2010 to 2014.

Of this group, 10 percent continued to fill opioid prescriptions with high daily opioid dose — equivalent to six tablets per day of 5-milligram hydrocodone — three months after surgery. Daily opioid doses remained at this level even one year after surgery.

"Five to six tablets a day would be typical for managing early postoperative pain," says Lee. "What's not typical is still taking that three to six months after surgery. Most surgeons expect their patients would be off opioids completely within two weeks of surgery."

Lee says the usage levels three to six months after surgery are comparable to those of chronic opioid users.

"To me, it's really shocking," Lee says. "We're trying to help these patients. We've performed this operation to cure them of their cancer. But we've left 1 in 10 as chronic opioid users. That's a tremendous burden to leave with cancer survivors."

Patients who were treated with chemotherapy after surgery had an even higher risk of new persistent opioid use, with 15 to 21 percent of them continuing to take opioids at high doses long past the recommended guidelines.

"Chemotherapy can cause painful complications," says Lee. "This kind of pain is challenging to treat, and opioids are often used to treat this even though they're not very effective for managing this kind of pain."

Potential solutions

"As a surgeon, patients will sometimes ask me, 'Is there a risk that I will get addicted to these medications?' and before we started this research, I would tell them the risk is very small," says Lee. "We now know that was the wrong thing to say."

SEE ALSO: Does Widespread Pain Stem from the Brain? MRI Study Investigates

Now that the problem has been identified, Lee is working with a team of researchers to address it.

"First and foremost, we need to make sure we're prescribing the appropriate amount," says Lee. "We're conducting follow-up studies to evaluate how much patients are actually taking, and using that information to prescribe lower amounts. What we've found in our initial work is people take far less than we prescribe. Having a lot of extra pills puts these patients at risk."

Lee says an equally important step is providing better pain management education to patients about opioids.

"That means that we shouldn't just hand them a pill bottle and say, 'This is for pain; take it and good luck,'" Lee says. "We should be telling them that this is for severe pain only. You should use Tylenol and Motrin first, and if the pain gets really bad, then you can take opioids as a last resort. We need to do a better job of counseling those patients on the risks associated with opioid use.

"The better we can educate patients, the less they'll take while still having the same amount of pain control."

Ultimately, though, it comes down to physician responsibility, Lee says.

"I think that the entire multidisciplinary care team really needs to pay attention to this issue," says Lee. "We need to do a better job taking care of these patients. We need to make sure they have adequate pain management, but we also need to make sure that we're not leaving them chronic opioid users."