Preliminary data shows that drug overdose deaths may have fallen by 5 percent in 2018 — the first drop in overdose deaths since the country’s opioid epidemic began in the 1990s.

The data, first reported by the New York Times, seems like good news. A 5 percent drop would amount to hundreds or even thousands of lives saved each year: According to the preliminary data from the Centers for Disease Control and Prevention, there were more than 68,000 drug overdose deaths in 2018, compared to more than 72,000 overdose deaths reported in the preliminary data for 2017. (The final data for 2017 put overdose numbers slightly lower — at a bit more than 70,000.) If nothing else, the figures suggest the opioid crisis may be starting to level off.

But there are also several reasons to be cautious about the report:

1) The latest CDC data is preliminary and subject to change. Overdose deaths could end up higher or lower than the data says right now. We just won’t know until the final figures come out later this year, likely around December.

The preliminary estimate for 2017 was off by roughly 2,000 overdose deaths. If the deviation is the same in 2018, but this time overdose deaths were undercounted, then 2018 could have been worse, not better, than 2017. We are just a margin of error from these numbers looking very different.

2) This isn’t the first time that it’s appeared the opioid epidemic has leveled off. Between 2011 and 2012, drug overdose deaths appeared to level off around 41,500. Then, dangerous synthetic opioids, particularly illicit fentanyl, seeped into the black market — and overdose deaths skyrocketed to 70,000 in 2017.

The fentanyl outbreak is still centered on parts of the Northeast and Midwest. If fentanyl starts to spread to other parts of the country in full force, overdose deaths could rise in other places too — and so would the overall death toll.

Or something unpredictable could happen, just like fentanyl took many people by surprise.

3) Overdose deaths from synthetic opioids, such as fentanyl, are still trending up, based on the preliminary CDC data: Synthetic opioid overdose deaths excluding methadone were estimated at nearly 32,000 in 2018, up from more than 29,000 in 2017. Deaths linked to cocaine and psychostimulants, like meth, also increased. Most of the drop in overdose deaths is linked to a fall in opioid painkiller deaths, as prescriptions to those drugs also fall. But if other overdose deaths continue to go up, they could overcome any drop in painkiller deaths.

4) Even if the drop in overdose death found in the preliminary data holds up, America still has an alarmingly high overdose death rate. At more than 68,000 drug overdose deaths, 2018 would still be the second-worst year for drug overdose deaths in US history — adding up to more than deaths linked to guns, cars, or even HIV/AIDS at its peak. This is not where the country should want to end up on drug overdoses.

There is some room for optimism. The painkiller numbers in particular suggest efforts to curtail prescriptions to those drugs are working, although there are some concerns about balancing out such efforts to make sure people with genuine need for painkillers can still get the drugs.

In the past few years, the federal government has also committed billions of additional dollars to addiction treatment and harm reduction efforts, such as distribution of the opioid overdose antidote naloxone, in response to the opioid crisis. While that’s far from the tens of billions that experts say is ultimately needed to fully reverse the epidemic, it’s still more funding — and it could be helping mitigate the crisis right now.

But the celebration should be tempered by the many caveats around the CDC data and the tens of thousands of overdose deaths that continue occurring each year in America.