The findings, published in the journal Addiction, raise questions about the effectiveness of Suboxone and addiction treatment in general, at a time when the federal government is spending hundreds of millions of dollars to subsidize the addiction treatment industry.

"The statistics are startling," said lead author G. Caleb Alexander, MD, "but are consistent with studies of patients treated with methadone showing that many patients resume opioid use after treatment."

Researchers say the continued use of pain medication during and after addiction treatment suggests that many patients did not have well-coordinated treatment for their addiction or their chronic pain.

“There are high rates of chronic pain among patients receiving opioid agonist therapy, and thus concomitant use of buprenorphine and other opioids may be justified clinically. This is especially true as the absence of pain management among patients with opioid use disorders may result in problematic behaviors such as illicit drug use and misuse of other prescription medications,” Alexander wrote.

Prescriptions for Suboxone and other brands of buprenorphine have soared in recent years as the U.S. grapples with an “opioid epidemic” that was initially fueled by painkillers, but is now increasingly caused by heroin and illicit fentanyl. Sales of buprenorphine now exceed $2 billion annually and are likely to keep growing.

Last year the federal government nearly tripled the number patients that can be treated with buprenorphine by an eligible physician. Raising the limit from 100 to 275 patients was intended to give addicts greater access to treatment, especially in rural areas where few doctors are certified to prescribe buprenoprhine.

An additional $1 billion in funding for addiction treatment was approved by Congress last year under the 21st Century Cures Act. Much of that money will be used to pay for buprenorphine prescriptions.

Addicts long ago discovered that buprenorphine can be used to get high or to ease their withdrawal pains from heroin and other opioids. Buprenorphine is such a popular street drug that the National Forensic Laboratory Information System ranked it as the third most diverted opioid medication in the U.S. in 2014.