More people than ever are dying from drug overdoses, with death tolls surpassing 72,000 in 2017, according to preliminary data out Wednesday from the Centers for Disease Control and Prevention.

The latest data, which won't be finalized until the end of this year, show that deaths from drug overdoses continue to rise, surpassing the record 63,632 deaths in 2016. The trend is a sign that public health officials are struggling in their efforts reduce death tolls amid the scourge of highly addictive, deadly opioids.

The increases in drug overdoses are largely propelled by opioids, which caused roughly 40,000 overdoses. Of these, 30,000 were from fentanyl, an opioid 50 times more potent than heroin. Fentanyl is made with chemicals in a lab, while heroin is made from the poppy plant.

Opioids kill people by making breathing slow or stop. Fentanyl, however, is especially lethal: Just a salt-shake amount into the palm is enough to kill most people.

The opioid crisis started with widespread prescribing in doctor's offices and hospitals of opioids such as OxyContin. As medical providers became more aware that people were becoming hooked to the drugs in the late 1990s and early 2000s, they limited them and patients turned to heroin, a cheaper, easily available alternative that affects the brain in a similar way. Health officials began to raise the alarm about the trend regularly late in former President Barack Obama's second term.

But in recent years, fentanyl has permeated the drug supply. Studies suggest that many drug users don’t know they've taken it, and instead intended to take cocaine or another drug. The early data released Wednesday suggests that deaths from prescription painkillers, methadone, and heroin fell in 2017.

The latest CDC data aren't final because deaths are still being investigated and because in many of the deaths, people have taken multiple drugs. Federal officials collect the information from states throughout each year.

The House passed a massive opioid bill in June, but Senate leaders have not yet announced whether they will vote on that version of the bill or pass their own measures. The Trump administration has said that combating the opioid crisis is a public health emergency and has released public service announcements on the issue, guidance to doctors, and advanced research on addiction and non-addictive pain medications.

The latest report suggests that the surge of drug overdoses hasn't shown a sign of slowing yet. Drug overdoses overall have contributed to lower life expectancy in the U.S. The latest figures could cause life expectancy to fall for the third year in a row, something that hasn't happened in 100 years. The cause the last time the U.S. hit that mark was an influenza epidemic that tore into the population during World War I, killing more people than combat did.