Experts have claimed that battery-powered e-cigarettes can do more harm than good, as they apparently contain harmful chemicals.
Two leading Greek researchers have advised consumers to stop using the devices until ongoing safety studies are reported back.
The popularity of e-cigarettes has increased as consumers can inhale nicotine without tar, tobacco or carbon monoxide.
However, the US Food and Drug Administration has expressed concern after learning different brands delivered markedly varied amounts of nicotine vapour with each puff.
They have detected traces of powerful cancer-causing chemicals too.
Also, private enterprise Health New Zealand has found cancer-causing chemicals in the product.
"The scarce evidence indicates the existence of various toxic and carcinogenic compounds in e-cigarettes, albeit in possibly much smaller concentrations than in traditional cigarettes," the BBC News quoted the researchers as saying.
Meanwhile, a Department of Health spokeswoman insisted the government was working to ensure e-cigarettes were labelled and sold appropriately.
She said: "The Department of Health is not aware of any evidence about the long-term safety of e-cigarettes and, as such, would suggest that consumers exercise caution.
"E-cigarettes are not promoted by, or available on, the NHS."
The study has been published in the British Medical Journal.