E-cigarettes produce more harm than good, a new study concludes. The researchers say the number of adults who use e-cigarettes to quit smoking is much lower than the number of teens and young adults who start smoking regular cigarettes after trying e-cigarettes.

They calculated 2,070 adult smokers who used e-cigarettes in 2014 would quit smoking regular cigarettes in 2015 and remain smoke free for at least seven years, according to Consumer Reports. They also estimated 168,000 teens and young adults who tried e-cigarettes in 2014 would start smoking regular cigarettes in 2015 and eventually become daily smokers. Overall, e-cigarette use in 2014 would lead to 1.5 million years of life lost, they estimated.

“If e-cigarettes are to confer a net population-level benefit in the future, the effectiveness of e-cigarettes as a smoking cessation tool will need to be much higher than it currently is,” the researchers wrote in the journal PLOS One.