The opioid crisis has been ongoing in the US for a number of years, with 446,032 Americans dying from drug overdoses between 1999 and 2018. Tackling this issue requires an understanding of the ever-shifting trends concerning fatal drug use, as the substances driving these statistics tend to change over time. According to a new report from the Centers for Disease Control and Prevention (CDC), the percentage of overdose deaths caused by heroin and prescription drugs has begun to decline across America, while synthetic opioids are becoming deadlier than ever.

The report reveals that the number of fatal overdoses in the US dropped by 4.1 percent from 2017 to 2018. Of the 70,237 drug-related deaths that occurred in 2017, 47,600 involved opioids, while this class of substance was responsible for 46,802 of the 67,367 deadly overdoses reported the following year.

This shift appears to be driven largely by a reduction in the number of prescription opioid overdoses, which caused 13.5 percent fewer deaths in 2018 than in 2017. The report suggests that this may be thanks to the measures that have been put in place to improve prescribing practices across the country, resulting in a drop in the number of opioid scripts being filled since 2012.

Heroin-related deaths were also down by 4 percent, which the CDC says is partly due to improved access to life-saving medications like naloxone, which reverses the effects of opioid overdoses if administered quickly enough. However, the report also explains that heroin use may have dropped as people have been switching to stronger synthetic opioids like fentanyl, which is notoriously deadly.

This is something that appears to be shown in the data, which reveals a 10 percent increase in deaths caused by synthetic opioids between 2017 and 2018. This figure excludes deaths caused by Methadone, a synthetic opioid that is commonly prescribed to help heroin addicts wean themselves off drugs. It is therefore likely that the vast majority of synthetic opioid-related overdoses are being caused by illicit drugs, with fentanyl the likeliest candidate.

Given the complexity of the issue, it’s hardly surprising that the picture is not uniform across the country, with different states experiencing greatly contrasting overdose trends. West Virginia, for instance, saw 42.4 opioid-related deaths per 100,000 people in 2018 – the highest rate of any state. Prescription opioid fatalities were also higher here than anywhere else, as were synthetic opioid-related deaths.

Vermont, meanwhile, saw the highest rate of deadly heroin overdoses in 2018, with 12.5 per 100,000 members of the population dying after using the drug.

The situation appears much more optimistic elsewhere, though, with Ohio witnessing the largest overall decrease in opioid-related deaths, largely thanks to a 40.5 percent drop in prescription opioid fatalities compared to the previous year.

Commenting on these figures, study author Nana Wilson explained in a statement that “Opioid overdoses decreased from 2017 to 2018 but still remain high. Efforts must be strengthened to maintain and accelerate decreases in deaths involving prescription opioids and heroin and to prevent continued increases in overdose deaths involving synthetic opioids.”