It’s easier than ever for doctors to prescribe a key medicine for opioid addiction since the U.S. government lifted an obstacle last year. But despite the looser restrictions and the ongoing overdose crisis, a new study finds little change in the number of people taking the medication.

Researchers analyzed prescriptions filled by U.S. pharmacies for the treatment drug buprenorphine. The number of prescribers rose last year after doctors no longer needed to get a special waiver to prescribe the drug, while the number of patients filling prescriptions barely budged.

It may take more than one year to see a bigger increase in patients, said study co-author Dr. Kao-Ping Chua of the University of Michigan Medical School.

“There are so many other barriers to prescribing that we have to address,” said Chua.

The findings were published Wednesday in the New England Journal of Medicine.