Adult smokers who didn’t use electronic vaping devices were more than twice as likely to quit, according to the study.

Makers of electronic cigarettes and other vaping devices often tout their products as smoking cessation aids. But new research suggests that the devices haven’t helped many U.S. smokers quit.

In a study published Monday in the journal PLOS One, researchers at Georgia State University found that U.S. adult smokers who didn’t use electronic vaping devices were more than twice as likely to quit as those who did.

Moreover, more than 90% of smokers who also vaped at the outset of the study were still smoking a year later, according to the study. More than half of these smokers were also still vaping.