Scientists have found that E-cigarettes are less addictive for smokers than cigarettes containing tobacco.

The popularity of e-cigarettes, which typically deliver nicotine, propylene glycol, glycerin and flavorings through inhaled vapor, has increased in the past 5 years, and currently there are more than 400 brands of 'e-cigs' available. E-cigs contain far fewer cancer-causing and other toxic substances than cigarettes, however their long-term effects on health and nicotine dependence are unknown.

Penn State College of Medicine researchers developed an online survey to study e-cigarette dependence, including questions designed to assess previous dependence on cigarettes and almost identical questions to assess current dependence on e-cigs. More than 3,500 current users of e-cigs who were ex-cigarette smokers completed the Penn State Cigarette Dependence Index and the Penn State Electronic Cigarette Dependence Index.

Higher nicotine concentration in e-cig liquid, as well as use of advanced second-generation e-cigs, which deliver nicotine more efficiently than earlier "cigalikes," predicted dependence. Consumers who had used e-cigs longer also appeared to be more addicted.

However, Prof. Jonathan Foulds said that people with all the characteristics of a more dependent e-cig user still had a lower e-cig dependence score than their cigarette dependence score. They think this is because they're getting less nicotine from the e-cigs than they were getting from cigarettes.

Although many regular users on e- cigarettes are trying to quit smoking, the Food and Drug Administration has not approved them for this use, and they cannot be marketed as a smoking cessation product.

The new questionnaire also allows for cross-comparisons between different nicotine and tobacco products. Foulds said that not only were e-cigs a booming industry, but new tobacco products were set to enter the market soon.

The findings are published in Nicotine and Tobacco Research.