The number of opioid painkillers prescribed in the United States has fallen significantly since peaking in 2010, a new analysis by the Centers for Disease Control and Prevention (CDC) has found. However, federal health officials say the nation’s struggle with opioid and heroin addiction is far from abated, The New York Times reports

The CDC analysis, which used retail prescription data from health tech company QuintilesIMS, found that overall, the number of opioids prescribed across the country fell 18 percent from 2010 to 2015, with prescriptions for higher, more dangerous doses dropping by 41 percent since then. But the report also noted that the prescribing rate in 2015 remained three times as high as in 1999, when health officials say the United States’ opioid crisis was just beginning.

The report also found that there are still vast regional differences in the number of opioids doctors dole out, with more prescriptions per capita in places like Maine, Nevada and Tennessee than in most of Iowa, Minnesota and Texas. What’s more, CDC researchers noted that opioid prescriptions increased in 23 percent of the counties surveyed.

Since it examined only prescribing data through 2015, the analysis did not take into account a series of recent attempts to reduce opioid addiction across the country, including CDC guidelines issued last year that set insurer limits on how many pills doctors can prescribe. However, the report noted that earlier actions, such as state crackdowns on local pain clinics, efforts by the Department of Veterans Affairs to curtail painkiller prescriptions and the federal government’s tightening of prescribing rules for hydrocodone in 2014 may have contributed to the declines.

However, addiction experts who commented on the study also warned that the study’s averages could be misleading. Digging deeper into the report, researchers noted that a lion’s share of opioid volume is still driven by a very small number of prescribers. The analysis also found that larger amounts of the highly addictive drugs appear to be prescribed in so-called micropolitan counties—urban clusters of 10,000 to 50,000 people anchored to larger rural regions—as well as in those with larger white populations, higher unemployment and higher Medicaid enrollment rates.

And despite the national decline in opioid prescriptions, the report found that the average number of days opioid prescriptions are meant to last has increased more than 70 percent since 2010.

“We still have too many people getting medicine at too high a level and for too long,” said the CDC’s acting director, Anne Schuchat, MD, adding that the quantity of opioids prescribed in 2015 alone would be enough to provide every American with 24/7 painkillers for nearly three weeks. 

Meanwhile, many parts of the United States continue to grapple with recent increases in opioid overdoses, new hepatitis C virus (HCV) infections and, in some instances, HIV outbreaks among injection drug users—many of whom started out taking prescription painkillers. The CDC report also noted that even if opioid prescribing continued to drop, it probably would not have an immediate effect on the country’s addiction epidemic because there are so many already addicted.