Costs related to narcotic painkillers are growing for workplace insurers, which are currently spending an estimated $1.4 billion on the drugs, The New York Times reports. The companies are facing payouts to workers with injuries who are being treated with opioids, including many who do not return to work for months—or who don't return at all.

Opioids can increase disability payouts and medical expenses by delaying employees' return to work, if the drugs are used too often, too early in treatment, or for too long. A study by the California Workers Compensation Institute conducted in 2008 found workers taking high doses of opioids to treat injuries, such as back strain, were out of work three times longer, compared to those with similar injuries who took lower doses of medication.

A 2010 study by the insurer Accident Fund Holdings found that when disability payments and medical care are combined, the cost of a workplace injury is nine times higher when a strong painkiller such as OxyContin is used, compared to when an opioid is not used, the article notes.

"What we see is an association between the greater use of opioids and delayed recovery from workplace injuries," Alex Swedlow, the head of research at the California Workers Compensation Institute, told the newspaper.

Although there is little evidence that opioids provide long-term benefits in treating common workplace injuries such as back pain, these drugs are widely prescribed for these problems.

Insurance industry data shows that between 2001 and 2008, opioid prescriptions as a percentage of all drugs used to treat workplace injuries rose 63 percent. Costs have also increased. To reverse this trend, some states have issued new pain treatment guidelines, or are expected to do so.