Drug overdose deaths in the U.S. went up slightly last year after two big leaps during the pandemic.

Officials with the Centers for Disease Control and Prevention say the numbers plateaued for most of last year. Experts aren't sure whether that means the deadliest drug overdose epidemic in U.S. history is finally reaching a peak, or whether it'll look like previous plateaus that were followed by new surges in deaths.

"The fact that it does seem to be flattening out, at least at a national level, is encouraging," said Katherine Keyes, a Columbia University epidemiology professor whose research focuses on drug use. "But these numbers are still extraordinarily high. We shouldn't suggest the crisis is in any way over."

An estimated 109,680 overdose deaths occurred last year, according to numbers posted Wednesday by the CDC. That's about 2% more than the 107,622 U.S. overdose deaths in 2021, but nothing like the 30% increase seen in 2020, and 15% increase in 2021.

While the overall national number was relatively static between 2021 and 2022, there were dramatic changes in a number of states: 23 reported fewer overdose deaths, one — Iowa — saw no change, and the rest continued to increase.

Eight states — Florida, Indiana, Kentucky, Maryland, Michigan, Ohio, Pennsylvania and West Virginia — reported sizable overdose death decreases of about 100 or more compared with the previous calendar year.

Some of these states had some of the highest overdose death rates during the epidemic, which Keyes said might be a sign that years of concentrated work to address the problem is paying off. State officials cited various factors for the decline, like social media and health education campaigns to warn the public about the dangers of drug use; expanded addiction treatment — including telehealth — and wider distribution of the overdose-reversing medication naloxone.

Plus, the stigma that kept drug users from seeking help — and some doctors and police officers from helping them — is waning, said Dr. Joseph Kanter, the state health officer for Louisiana, where overdose deaths fell 4% last year.

"We're catching up and the tide's turning — slowly," said Kanter, whose state has one of the nation's highest overdose death rates.

Beginning in the mid-1990s, abuse of prescription opioid painkillers was to blame for deaths before a gradual turn to heroin, which in 2015 caused more deaths than prescription painkillers or other drugs. A year later, the more lethal fentanyl and its close cousins became the biggest drug killer.

Last year, most overdose deaths continued to be linked to fentanyl and other synthetic opioids. About 75,000, up 4% from the year before. There also was a 11% increase in deaths involving cocaine and a 3% increase in deaths involving meth and other stimulants.

Overdose deaths are often attributed to more than one drug; some people take multiple drugs and officials say inexpensive fentanyl is increasingly cut into other drugs, often without the buyers' knowledge.

Research from Dr. Daniel Ciccarone, a drug policy expert at the University of California, San Francisco, suggests "there appears to be some substitution going on," with a number of people who use illicit drugs turning to methamphetamines or other options to try to stay away from fentanyl and fentanyl-tainted drugs.

Ciccarone said he believes overdose deaths finally will trend down. He cited improvements in innovations in counseling and addiction treatment, better availability of naloxone and legal actions that led to more than $50 billion in proposed and finalized settlements — money that should be available to bolster overdose prevention.

"We've thrown a lot at this 20-year opioid overdose problem," he said. "We should be bending the curve downward."

But he also voiced some caution, saying "we have been here before."

Consider 2018, when overdose deaths dropped 4% from the previous year, to about 67,000. After those numbers came out, then-President Donald Trump declared "we are curbing the opioid epidemic."

But overdose deaths then rose to a record 71,000 in 2019, then soared during the COVID-19 pandemic to 92,000 in 2020 and 107,000 in 2021.

Lockdowns and other pandemic-era restrictions isolated people with drug addictions and made treatment harder to get, experts said.

Keyes believes that 2022's numbers didn't get any worse partly because isolation eased as the pandemic ebbed. But there may be issues ahead, others say, like increased detection of veterinary tranquilizer xylazine in the illicit drug supply and proposals to scale back things like prescribing addiction medications through telehealth.

"What the past 20 years of this overdose crisis has taught us is that this really is a moving target," Keyes said. "And when you think you've got a handle on it, sometimes the problem can shift in new and different ways."