Researchers from the U.S. National Cancer Institute (NCI) used what they noted was “high-quality death certificate data” from the World Health Organization Mortality Database from the years 2001 to 2015 to conduct the survey. Other nations included were Australia, Chile, Denmark, England and Wales, Estonia, Finland, Germany, Mexico, the Netherlands, Norway, and Spain. Data from England and Wales was combined for the study’s purposes.

In the U.S. in 2015, drug overdoses accounted for 35 deaths in 100,000 men and 20 deaths in every 100,000 women, according to a report on the survey in U.S. News and World Report. Men’s overdose deaths typically occur at double the rate of women in a particular population. In comparison with the U.S., the next highest rate was found in Estonia, where drug overdoses accounted for 20 deaths per 100,000 men.

While troubling, this doesn’t come as a total shock to anyone paying attention how U.S. drug overdose rates have been climbing in recent years, with a record-number 71,568 Americans dying from drug overdoses in 2017 alone, according to the Centers for Disease Control and Prevention (CDC). Drug overdoses now outpace other fatalities including suicide and death from the flu and pneumonia, and that’s largely caused by the growing opioid crisis, including deaths caused by potent synthetic opioids such as fentanyl. In 2016, fentanyl accounted for nearly half of all overdose deaths, a previously unheard-of rate.

Researchers have also noted that in the 21st century, drug overdose mortality rates in the U.S. have more than doubled.