(CNN) Adult smokers who vape are more likely to quit using cigarettes, according to a study released Monday. But e-cigarettes also increase the risk of relapse in some former smokers, the researchers found.

"This study is the first to point out that even if smokers may succeed in stopping smoking with the aid of electronic cigarettes, they still need to be monitored by doctors and health professionals to prevent a relapse in the long term," said Ramchandar Gomajee, the paper's lead author and a researcher at France's Pierre Louis Institute of Epidemiology and Public Health.

The findings suggest that e-cigarette use may affect current and former smokers differently: helping people addicted to cigarettes kick the habit, perhaps, but also drawing some who had already quit back to smoking.

The study, published in the medical journal JAMA Internal Medicine, tracked more than 5,000 daily smokers for an average of two years in France. It found that smokers who vaped used fewer cigarettes per day and were more than one and a half times as likely to quit completely.

But researchers also looked at more than 2,000 former smokers and found that those who used e-cigarettes were more likely to relapse back to smoking. "Thus, while [e-cigarette] use can help persons reduce their smoking levels in the short term," the researchers wrote, "there is no evidence that it is an efficacious smoking cessation aid in the long term."