(Reuters Health) - Online black-market sales of opioid painkillers more than doubled in the United States during the two years after these drugs were “rescheduled,” putting tighter restrictions on legal prescriptions and sales, according to a recent study.

In October 2014, hydrocodone combination products - the most popularly prescribed opioid pain relievers - were reclassified from the U.S. Drug Enforcement Administration’s schedule III to schedule II, imposing stricter controls on prescriptions written by doctors and on patients’ ability to refill them.

Almost immediately, the proportion of all drugs illicitly purchased in the U.S. from sellers on the “dark net” that were in the opioid category began rising, reaching 13.7 percent in 2016. Stronger, more dangerous opioids also gained in popularity in these so-called cryptomarkets, including fentanyl, which went from least common to the second most commonly purchased opioid, the study team found.

“As drug researchers, we are obviously acutely aware of the opioid crisis in the USA and the attempts to control it,” said one of the study authors, Jack Cunliffe, a researcher with the University of Kent in Canterbury, UK. They are also aware that interventions to reduce supply “have a history of pushing things to the black market - as the Iron Law of Prohibition states,” he said in an email.

The Iron Law of Prohibition refers to the idea that reducing supply through increased enforcement and changes to drug availability lead to illicit markets dominated by higher potency products, he and his colleagues write in The BMJ.

Indeed, the study team also found that illegal sales of the more potent opioids, oxycodone and fentanyl, increased by the greatest amounts in these cryptomarkets.

“Our dataset covered the period of the federal hydrocodone re-scheduling and, as a researcher interested in causal analysis, the initial approach was to see if we’d observe what we thought we’d observe - i.e. an increase (in cryptomarket sales) of prescription opioid set against no changes elsewhere,” Cunliffe said.

The researchers used special software to analyze drug sales in 31 of the world’s largest cryptomarkets operating from October 2013 to July 2016. They focused on six product types: prescription opioids, prescription sedatives, prescription steroids, prescription stimulants, other prescription drugs and illicit opioids such as heroin.

Based on sales before and after the opioid rescheduling, they saw no change in purchases of opioids from outside the U.S., and no changes in any other drug categories. But their model projected that opioids would have represented 6.7 percent of all drugs purchased in the U.S. from cryptomarkets without the schedule change. Instead, opioid market share was more than twice that by July 2016.

The study provides clear evidence that to solve the opioid crisis the approach should be to reduce demand and not to simply cut off supply, Cunliffe said.

“We demonstrate that cutting off supply leads to people sourcing their drugs from illegal and uncontrolled sources, and they buy products of higher strength - with all the dangers that this type of supply carries,” he said.

A better approach would be harm reduction, therapeutic intervention, reliable treatment options, dealing with over-prescription early on, and providing information on the danger of opioid use to reduce stigmas, Cunliffe added.

The study wasn’t a controlled experiment and doesn’t prove that DEA rescheduling of opioid products caused the surge in cryptomarket sales, the researchers acknowledge.

“The Martin et al study adds to a mounting body of evidence that multiple efforts to restrict access to prescription opioids coincided with efforts by many opioid users to access these drugs on the black market,” said Leo Beletsky, an associate professor of law and health sciences at Northeastern University in Boston, who co-authored an editorial accompanying the study.

The emergence of cryptomarkets during this time functioned as “disruptive innovation” in how people can obtain drugs outside legitimate channels, Beletsky said in an email.

“Demand for opioids in the U.S. will decrease sustainably only when high quality, evidence-based prevention and treatment programs are broadly implemented, robustly funded, and universally accessible,” Beletsky and Dr. Scott Hadland, a pediatrician with the Grayken Center for Addiction at Boston Medical Center, write in their commentary.

“Taken together, policy measures like up-scheduling, an introduction of abuse-deterrent formulations, prescribing limits, and prosecuting health care providers created a powerful push that precipitated the changes in the overdose dynamics we are contending with today,” Beletsky told Reuters Health.

SOURCE: bit.ly/2JU7nZy and bit.ly/2lmKu2n The BMJ, online June 13, 2018.