The grip of opioid addiction is so strong that many people who undergo treatment relapse repeatedly. Now a study by Johns Hopkins University researchers offers new clues about why treatment is so difficult.

The researchers discovered that 43 percent of people receiving buprenorphine, a widely used anti-addiction medication, filled at least one prescription for opioids — which they presumably consumed or diverted to others.

They also found that the average length of stay on buprenorphine was just 55 days, much less than the months or years that experts believe it may take to conquer a substance-abuse disorder with the help of such drugs. Once patients stopped getting the anti-addiction medication, two-thirds of them went back to filling prescriptions for opioids, according to the study, published Thursday in the journal Addiction.

Caleb Alexander, co-director of the Center for Drug Safety and Effectiveness at the Johns Hopkins Bloomberg School of Public Health, said his team's research "raises important questions about the quality of care these patients are receiving and the degree to which their care is coordinated across our fragmented health-care system."

Alexander said people receiving medication-assisted treatment with buprenorphine or methadone may see one provider for that drug, another for their primary care and yet another if they are brought to an emergency room. Despite the growth in many states of databases designed to help providers track a patient's drug purchases, doctors are often unaware of what other physicians may be prescribing.

Inefficiency and poor communication are to blame much more than drug-seekers trying to manipulate the system, Alexander said.

"The big concern is fragmentation of care," he said. The databases, known as prescription drug monitoring programs, "are not a panacea," he added. "Many doctors don’t use them. Many doctors aren’t even registered. Many who are registered don’t use them regularly."

"I don’t think we can put this entirely on patients or providers or any other single stakeholder," Alexander said.

The study looked at the records of 38,096 buprenorphine users in 11 states between January 2010 and July 2012. Because buprenorphine is sometimes prescribed for pain, the researchers analyzed a subset of those people who received a form of the drug, Suboxone, that is only prescribed to combat the cravings of opioid addiction. Even among those 20,124 people, 27 percent used another opioid during treatment, and 54 percent received one after treatment ended.

The National Institute on Drug Abuse puts the relapse rate for drug addiction at 40 to 60 percent, which is similar to the rate at which people with other chronic diseases suffer setbacks.

Despite the discouraging statistics, research shows that medication-assisted treatment is one of the most successful and common ways to combat addiction.

"But our study raises important questions about the real-world quality of medication-assisted treatment," Alexander said.