Like conventional cigarettes, electronic ones may function as a "gateway drug" that can prime the brain to be more receptive to harder drugs, US researchers said on Wednesday.

The findings add to the debate about the relative risks and benefits of electronic cigarettes, the increasingly popular devices that deliver nicotine directly without burning tobacco.

"With e-cigarettes, we get rid of the danger to the lungs and to the heart, but no one has mentioned the brain," said Dr Eric Kandel of Columbia University, the co-author of the report published in the New England Journal of Medicine.

In laboratory studies, the researchers showed that "once mice and rats are on nicotine, they are more addicted to cocaine" after being introduced to that drug, said Dr Aruni Bhatnagar of the University of Louisville, who was not involved in the study but chaired a 10-member American Heart Association panel on the impact of e-cigarettes.

That was true even when the mice received nicotine without burning tobacco, Kandel told Reuters in a telephone interview.

Kandel won a Nobel Prize in 2000 for his work on memory.

The findings by Kandel and his wife, Columbia University researcher Denise Kandel, expand on her earlier work on nicotine as a "gateway drug", a theory she first reported on in 1975.

"E-cigarettes have the same physiological effects on the brain and may pose the same risk of addiction to other drugs as regular cigarettes, especially in adolescence during a critical period of brain development," they wrote.

Although it is not yet clear whether e-cigarettes will prove to be a gateway to the use of conventional cigarettes and illicit drugs, they said "that's certainly a possibility".

"Nicotine clearly acts as a gateway drug on the brain, and this effect is likely to occur whether the exposure comes from smoking cigarettes, passive tobacco smoke, or e-cigarettes," they wrote.

Electronic cigarettes are now a $3 billion business with 466 brands that include candy flavoring and are increasingly popular among youth, according to the World Health Organization.

Using 2004 epidemiologic data from a large, longitudinal sample, Denise Kandel found that the rate of cocaine dependence was highest among users who started using it after having smoked cigarettes.

Dr Shanta Rishi Dube of the Georgia State University School of Public Health, who was not involved in the research, said the results "appear valid based on prior studies that have looked at nicotine as a potential gateway".

Bhatnagar said the findings strengthen the case for regulation of e-cigarettes by the US Food and Drug Administration.

(China Daily 09/05/2014 page10)