But while e-cigarettes may be designed to help people quit smoking, according to recent research they may act as a "gateway" to harmful illicit drugs.
Like conventional cigarettes, the devices are said to raise the risk of addiction to banned substances such as cannabis and cocaine.
Scientists pointed out that while eliminating many of the toxic compounds found in tobacco, e-cigarettes delivered highly addictive "pure nicotine".
In mice, nicotine was found to alter brain biochemistry and prime the animals to develop a need for cocaine.
Analysis of human data suggested it had the same effect in people, with cocaine addiction rates highest among former cigarette smokers.
"Our findings provided a biological basis for the sequence of drug use observed in people," US neuroscientist Professor Eric Kandel, who conducted the research with his wife, Dr Denise Kandel, said.
"One drug alters the brain's circuitry in a way that enhances the effects of a subsequent drug."
Writing in the New England Journal of Medicine, the married couple from Columbia University, New York, warned: "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."
The typical e-cigarette user is a long-term smoker who has been unable to quit, they said.
But popularity of the devices was increasing at an accelerating rate among adolescents and young adults.
"The effects we saw in adult mice are probably even stronger in adolescent animals," said Eric Kandel, who in 2000 shared the Nobel Prize in Physiology or Medicine for his research on the physiological basis of memory.
"E-cigarettes may be a gateway to both combustible cigarettes and illicit drugs.
"Therefore, we should do all we can to protect young people from the harmful effects of nicotine and the risks of progressing to illicit drugs."
His wife added: "The recent legalisation of marijuana in Colorado and Washington has rekindled the debate about whether marijuana is a gateway drug.
"Yet both proponents and opponents of legalisation have overlooked the role of nicotine in leading to the use of illicit drugs and to addiction."
Professor Jeffrey Lieberman, chair of psychiatry at Columbia University Medical Center, said: "The emergence in our society of new recreational pharmaceuticals such as e-cigarettes and legalised marijuana, while justifiable on one level, may have adverse consequences of which we are not fully aware.
"The Kandels' research on 'gateway' drugs demonstrates such grave potential consequences."
More than a million people in the UK are believed to get their nicotine "fix" from e-cigarettes, but opinion is divided about the safety of the devices.
E-cigarettes have a surprisingly long history dating back to 1963 when Herbert A Gilbert, a 40-a-day smoker from Beaver Falls, Pennsylvania, filed a patent for a "smokeless non-tobacco cigarette".
His invention worked by gently heating a nicotine solution to produce a vapour that could be inhaled, thereby "replacing burning tobacco and paper with heated, moist, flavoured air".
But at a time when 70% of adult males in the UK alone were regular smokers, he failed to secure financial backing for the idea.