Summary of Studies on Long-Term Opioid Use

People who have severe, chronic pain may be given the option of taking opioid medications (narcotics) to help manage their pain and live some semblance of a normal life. For those who are not facing end-of-life issues with cancer, this can become a life-long management tool. Whenever opioids are discussed, there is always a concern raised about physical dependency and addiction.

But as the authors of this study point out, addiction isn’t the only downside of opioids. Difficulty concentrating, memory loss, slower physical reaction time, and slower processing of information are additional potential side effects of these powerful pain relievers. What’s the current evidence that such effects on cognitive function are really a problem?

To find out, pain experts from Denmark, Sweden, and Brazil teamed up to review data published in medical and psychologic journals around the world. They summarized the results in a table that included type of study (design), sample size (number of patients), type and dose of opioid, and outcomes.

A total of 13 studies met the inclusion criteria and were analyzed and included in the table. All studies were examining non-cancer patient groups who had chronic pain. When it comes to the design of each study, the most common types of study were randomized controlled trials (RCTs), comparative studies, and observational studies.

As the names suggest, a randomized controlled trial means patients were placed randomly in one of several groups being tested and studied. Random selection can be done by a computer or the patients can be assigned to the next available group as they enter the study. Comparative studies look at the results of a group of normal, healthy adults contrasted with those individuals receiving opioids. Observational studies just watch what happens and record the results for a specific type of treatment.

After reviewing and summarizing all 13 studies, the final conclusion was that information about the effect of long-term use of opioids on cognitive function in noncancer patients is still very limited. Whether they do harm, benefit, or don’t affect cognitive function at all remains unclear.

In cases where there was improvement in mental processing there were some things about the studies that didn’t measure up so the results weren’t as strong as would be hoped for. And some of the comparative studies were good but each study compared patients on long-term opioids to different groups.

For example, one study looked at healthy people as the comparative group while another study studied chronic pain patients who did not take opioids. Sometimes the comparative group had similar neurologic problems as the main study group, while others did not select patients with neurologic deficits for the comparative group. Without a consistent comparative group, it becomes difficult if not impossible to get meaningful information. It’s too much like comparing apples to oranges.

One other problem observed in the studies that were available was the fact that many patients taking long-term opioids for non-cancer problems are also taking other medications. Some of those drugs have the ability to alter cognitive function. So then it becomes a problem identifying how much and what kind of effects occur with the opioid prescription.

And as is often the case, people who suffer from chronic pain become depressed. Altered mood or depression is also linked with changes in cognitive function (especially speed of mental or motor processing). Sorting out which factor has the most power over mental abilities can be difficult.

Some recommendations can still be made on the basis of these findings. But the strength of the advice is weaker than if there were coming from multiple high-quality studies with strong evidence. First, keep in mind the goals of pain control: to reduce the intensity of pain so the person can function better (mentally and physically). Better function can mean improved quality of life.

Second, keep in mind that long-term use of opioids can be harmless and even beneficial but use does come with some risks. Those risks have been mentioned including tolerance, addiction, and altered mental and/or motor function. Patients and their families should be fully informed about the benefits and risks of long-term opioid use.

Third, prescribing physicians must monitor their patients for signs of cognitive impairment. This is especially important for patients who are working, driving, or operating equipment. Periodic tests of cognitive function should be given to assess changes in mental processing. There are many different test measures available that show even slight changes or shifts in physical or mental function.

And finally, the results of this review of evidence about the long-term effects of opioid-use by non-cancer, chronic pain patients point out the need for future (improved) studies in this area. High-quality studies with matching designs are needed to really assess the potential harm, benefit, or no-effect of long-term (even lifelong) use of these powerful drugs.

The authors suggest that anyone who is given a prescription for opioids should be given a simple baseline test to assess cognitive function. Then if it turns out the prescription becomes a long-term event, retesting can be done. Any observed change(s) in cognitive function signal the need to review the medication and possibly change the drug or drug dosage.

At the same time, the more patients who are formally tested for cognitive effects, the more likely equal comparisons can be made between groups. Future review studies like this one would have more data to go on and a better chance of making helpful recommendations.