"We found that e-cigarettes appear to be less addictive than tobacco cigarettes in a large sample of long-term users," said Jonathan Foulds from the Pennsylvania State University College of Medicine.
The popularity of e-cigarettes, which typically deliver nicotine, propylene glycol, glycerin and flavourings through inhaled vapour, has increased in the past five years.
E-cigarettes contain far fewer cancer-causing and other toxic substances than cigarettes, however their long-term effects on health and nicotine dependence are unknown, researchers said.
To study e-cigarette dependence, researchers developed an online survey, including questions designed to assess previous dependence on cigarettes and almost identical questions to assess current dependence on e-cigarettes.
Higher nicotine concentration in e-cigarettes liquid, as well as use of advanced second-generation e-cigarettes, which deliver nicotine more efficiently than earlier 'cigar-likes' predicted dependence. Consumers who had used e-cigarettes longer also appeared to be more addicted.
"However, people with all the characteristics of a more dependent e-cigarette user still had a lower its dependence score than their cigarette dependence score," Foulds said.
"We think this is because they're getting less nicotine from the e-cigarettes than they were getting from cigarettes," Foulds said.
"It has the potential to do good and help a lot of people quit, but it also has the potential to do harm. Continuing to smoke and use e-cigarettes may not reduce health risks. Kids who have never smoked might begin nicotine addiction with e-cigarettes. There's a need for a better understanding of these products," Foulds said.
The findings also have implications for developing e-cigarettes for smoking cessation.
"We might actually need e-cigarettes that are better at delivering nicotine because that's what is more likely to help people quit," Foulds added.
The study was published in the journal Nicotine and Tobacco Research.

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