A new government study suggests the number of US adults who have tried electronic cigarettes may be leveling off.

The proportion of adults who have ever used e-cigarettes rose from about 3% to 8% from 2010 to 2012. But there was no significant change last year, according to the CDC study published in Nicotine & Tobacco Research.

The study’s conclusions seem to parallel a modest decline in e-cigarette sales during the same period that have been noted in analyst reports.

The findings come from an annual survey of thousands of adults. It has been the CDC’s only source on e-cigarette trends since the devices started selling in the US in late 2006.

“The long-term public health impact of these products is uncertain,” the study’s lead author, Brian King, said Wednesday. But he called the leveling off in adults who have ever tried e-cigarettes “a positive note.”

The study also found the percentage of adults who are described as current e-cigarette smokers—that is, they said they’d used one at least once in the previous 30 days—has been hovering at around 2 percent.