Experts have warned the public to wait for more evidence before purchasing and consuming e-cigarettes.
Writing in the British Medical Journal today (January 20th), Andreas Flouris and Dimitis Oikonomou from the Institute of Human Performance and Rehabilitation in Greece, highlighted the lack of evidence concerning e-cigarettes.
The tobacco substitutes are widely available despite a lack of conclusive evidence regarding the safety of their long-term use.
Drs Oikonomou and Flouris said: "Our knowledge on the acute and long term effects of e-cigarette use is, at best, very limited."
They urged the public to exercise caution, and if possible, wait for at least another year for further research regarding the prolonged use of the product.
E-cigarettes, or electronic cigarettes, are battery operated items which allow users to inhale a nicotine vapour.
Retailers recommend them because they lack the tar and chemicals found in traditional cigarettes.