By Pat Anson, Editor
Estimating rates of opioid abuse and addiction has never been easy. Dozens of different studies have come to startling different conclusions, and there is even disagreement over the definition of abuse and addiction.
Now a professor at the University of New Mexico is weighing in on the subject -- and his conclusions are likely to stir even more debate.
In a systematic review of 38 research reports (a study of studies) published in the journal PAIN, lead author Kevin Vowles and his colleagues estimate that up to 30 percent of the opioids prescribed for pain are misused and that about 10 percent of pain patients are addicted to them.
They also question whether opioids should be prescribed at all for chronic pain.
“It is not clear whether the risks of opioid use outweigh the potential for benefit. The efficacy of opioids and their suitability for the long-term management of chronic pain still remain very much in question and while this uncertainty in effectiveness is well established, it stands in somewhat stark contrast to the clinical reality of chronic pain treatment, where rates of prescriptions have skyrocketed such that opioids are now among the most frequently prescribed medications,” wrote Vowles.
“We are not certain whether the benefits derived from opioids, which are rather unclear based on the extant literature, compensate for this additional burden to patients and health care systems.”
The researchers noted there was extremely wide variation in the rates of opioid misuse and addiction in the studies they analyzed. Rates of “problematic use” ranged from less than 1% all the way up to 81%.
One study -- a review of 25 research reports – left the barn door wide open by broadly estimating the “prevalence of problematic opioid use behavior” at 0% to 50% of pain patients.
“The vagueness inherent in these definitions, areas of overlap among them, and their sometimes interchangeable use have made it difficult to determine exact rates and types of problematic opioid use,” conceded Vowles.
Exactly what constitutes opioid misuse is also debatable.
Vowles defined misuse as “opioid use contrary to the directed or prescribed pattern of use, regardless of the presence or absence of harm or adverse effects.” Such a definition means a patient who has stopped using a prescribed opioid – even if they no longer have pain – is misusing the medication.
(Several years ago this writer was sent home from the hospital after surgery with a two week supply of Vicodin. Fortunately, the surgery was successful and the pain subsided after a few days. A half empty bottle of Vicodin sat unused in my medicine cabinet for years before I had sense enough to throw it out. Under Vowles’ definition, I had “misused” the Vicodin.)
Studies by some of the nation’s largest drug screening companies consistently show that many Americans don’t take the drugs that are prescribed for them. A large study by Quest Diagnostics found that 60% of Americans failed to take a medication as prescribed by their physicians and that 42% had no drugs in their system. Should they be included in estimates of misuse?
Rates of addiction in the studies analyzed by Vowles also varied greatly – from 0.7% of pain patients up to 34.1%.
An adjusted analysis by Vowles estimated the average rate of addiction at 8% to 12% -- a figure nearly double the estimate of the National Institutes of Health (NIH). According to the NIH, only about 5% of patients taking opioids as directed for a year end up with an addiction problem.
“Misuse, abuse and addiction mean different things to different researchers,” said Lynn Webster, MD, past president of the American Academy of Pain Medicine and vice president of scientific affairs at PRA Health Sciences.
“We must keep in mind that behaviors determine the diagnoses of misuse, abuse and addiction and these behaviors are subjective interpretations. Subjective interpretations are influenced by one's biases and perspective. Misuse to one researcher can be addiction to another. Unfortunately there has not been a standard interpretation of behaviors and I doubt there ever will be due to personal beliefs about opioids and addiction.”
While Webster doesn’t take issue with the design of the study – he does dispute the overall conclusion that the risks of opioid abuse outweigh the benefits.
“It is undoubtedly true that some people should not be prescribed opioids. But even using their reported averages for abuse and addiction, a majority of people do not abuse or become addicted and therefore shouldn't necessarily be denied treatment particularly if there is no other option,” Webster wrote in an email to Pain News Network.
Ironically, only one study analyzed by Vowles even looked at the recreational abuse of opioids – perhaps the biggest contributor to the so-called “epidemic” of prescription drug abuse in the U.S. That study estimated the rate of abuse by pain patients at just 8% -- far below their estimated rates of misuse.
Vowles admits there are several limitations to his study.
“The most obvious is the degree of variability within this literature. In spite of our attempts to minimize the impact of this variability, the range of misuse and addiction was incredibly broad,” he wrote.
“These sources of variability will likely continue to cloud our ability to make precise estimates. There is clearly room here for a series of carefully controlled studies where sources of variability are held constant, or as constant as possible, to more clearly illuminate prevalence rates of problematic opioid use in individuals with chronic pain.”