Researchers from Columbia University Medical Center (CUMC) found that e-cigarettes may function as a "gateway drug" - a drug that lowers the threshold for addiction to other substances, such as marijuana and cocaine.
"While e-cigarettes do eliminate some of the health effects associated with combustible tobacco, they are pure nicotine-delivery devices," said co-author Denise B Kandel, professor of sociomedical sciences (in psychiatry), Department of Psychiatry and Mailman School of Public Health, at CUMC.
In the study published in the New England Journal of Medicine, researchers Denise and Eric Kandel reviewed her earlier work on the gateway hypothesis and on the role of nicotine as a gateway drug, reported in a Science paper in l975.
They also reviewed subsequent studies in which they tested the gateway hypothesis experimentally in a mouse model.
In those studies, conducted in collaboration with Amir Levine, Yan You Huang, Bettina Drisaldi, Edmund A Griffin, and others at CUMC, they found that when mice are exposed to nicotine, it alters their brain biochemically and induces activation of a reward-related gene.
As a result, nicotine primes the animals' subsequent response to cocaine, providing a molecular basis for nicotine as a gateway drug for cocaine.
Denise Kandel's further analysis of 2004 epidemiologic data from a large, longitudinal sample suggested that nicotine also primes human brains to respond to cocaine.
She found that the rate of cocaine dependence was highest among users who started using cocaine after having smoked cigarettes.
"Our findings provided a biologic basis for the sequence of drug use observed in people. One drug alters the brain's circuitry in a way that enhances the effects of a subsequent drug," said Eric Kandel.
"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.
"We don't yet know whether e-cigarettes will prove to be a gateway to the use of conventional cigarettes and illicit drugs, but 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," he said.