Experts have expressed fears that not enough is known about the safety of electronic cigarettes.
So-called 'e-cigarettes' are battery-operated devices that allow users to breathe in a nicotine vapour, rather than smoking actual cigarettes.
However, the US Food and Drug Administration has previously expressed concern after detecting a number of toxins in e-cigarettes.
In contrast, a private body called Health New Zealand recommends the devices as a safer alternative to regular tobacco products, while a publicly-funded Greek research institute called Demokritos has taken a neutral stance.
Writing in the British Medical Journal, Andreas Flouris and Dimitris Oikonomou, from the Institute of Human Performance and Rehabilitation in Greece, conceded that 'alternative smoking strategies are always welcome in an effort to reduce the threat to public health'.
However, they emphasised that more research is needed, as our knowledge of the long-term effects of e-cigarette use is 'at best, very limited'.
According to the Electronic Cigarette Company, e-cigarettes are the latest celebrity 'must-have' item.
The company's website features images of a number of well-known faces, including Leonardo DiCaprio, Lindsay Lohan and Kate Moss, using its products.