The study shows users are more likely to develop lung disease, such as chronic bronchitis or emphysema.
And if you smoke both e-cigarettes and tobacco cigarettes, which many people do, then you're more than two and a half times likely to develop lung problems.
The researchers also say vaping doesn't necessarily help people kick the habit.
The FDA says e-cigarette makers can say they are an alternative to traditional cigarettes, but they cannot claim to help you quit smoking, nor can they say they are "much safer" than combustible cigarettes.