NEW YORK (AP) — U.S. overdose deaths last year likely fell for the first time in nearly three decades, preliminary statistics suggest.

The Centers for Disease Control and Prevention posted the provisional numbers showing nearly 68,000 drug overdose deaths were reported last year. The number may go up as more investigations are completed, but the agency expects the tally will end up below 69,000.

Overdose deaths had been climbing each year since 1990, topping 70,000 in 2017.

The numbers were celebrated by the U.S. secretary of health and human services. “Lives are being saved, and we’re beginning to win the fight against this crisis,” Alex Azar wrote in a tweet.

But the overdose death rate is still about seven times higher than it was a generation ago.

Researchers do not believe this is the start of a dramatic decline. Data from the first months of this year likely will show the decrease lessen a bit rather than accelerate, said Farid Ahmad of the CDC’s National Center for Health Statistics.

The improvement was driven by a drop in deaths from heroin and prescription painkillers. Those falls were offset somewhat by continuing growth in deaths involving fentanyl, cocaine and psychostimulants like methamphetamines. Overdose deaths often involve more than one drug.

It can take months for authorities to complete toxicology tests and other elements of a death investigation involving drugs. And some states report faster than others. The CDC is expected to report more complete data later this year.

The current overdose epidemic has killed more people than any other in U.S. history, and it had been on a soaring trajectory. From 2014 to 2017, overdose deaths jumped by 5,000 or more each year.

Experts trace the epidemic’s origins to 1995 and the marketing of the prescription painkiller OxyContin. It was meant be safer and more effective than other prescription opioids, but some patients found themselves hooked and drug abusers found they could crush the tablets and snort or inject them to get high.

Gradually, more addicts turned to cheaper street drugs such as heroin and fentanyl. In 2015, heroin began causing more deaths than prescription painkillers or other drugs. In 2016, fentanyl and its close cousins became the biggest drug killer, and in 2018 they were involved in about 46 percent of the reported overdose deaths, according to the preliminary CDC data.

Strategies to reduce drug overdose deaths have included tougher policing, treatment program expansions, policies to limit opioid painkiller prescriptions and wider distribution of the overdose-reversing drug naloxone.

Haffajee and other researchers are trying to figure out what measures are most responsible for the slight improvement.