Vapers around the world can breathe easy knowing that E-cigarettes are not harmful, according to new research.
A leading vape brand carried out the two year, 200 person study that found the tobacco alternative does not damage the heart or lungs or cause any health problems.
It backs claims that the smoking devices are a safer option than cigarettes used by an estimated three million Britons, say scientists.
The volunteers were monitored for illness, had their lung function examined and had exposure to nicotine measured.
They also underwent electrocardiograms that monitor heart rate.
Lead author Tanvir Walele, director of scientific affairs at Amsterdam based Fontem Ventures which makes e-cig brand blu, said: "This study shows after two years of continual e-cigarette use, there were no signs of serious health complications in smokers."
The 24 month clinical trial reported in Regulatory Toxicology and Pharmacology showed smokers who used vaping products suffered no harm.
No serious safety concerns were recorded or clinically relevant findings observed in all medically-defined safety criteria.
Incredibly, the use of the vaping products actually revealed a reduction in nicotine withdrawal symptoms.
It also reduced participants exposure to cigarette smoke constituents, and there was no increase in their body weight.
Mr Walele: "Clinical data over a two year period gives us a much clearer picture about longer term vaping, and the potential implications for the health of smokers, so they can make an informed decision."
He said it follows a scientific review last year that found smokers who used e-cigs in the short to medium term - for two years or less - had no increased health risks compared to smokers who did not use them.
They could also help conentional cigarette smokers reduce or quit their habit. But that team said there is just a small number of published clinical studies currently available, and more research is needed.
Mr Walele said: "Governments and policy-makers should ensure that regulatory frameworks reflect this emerging scientific consensus, as more long term research demonstrates the safety profile of e-cigarettes.
"This research suggests we need e-cigarette regulation that is not modelled on tobacco product regulation, but encourages innovation and compliance with robust product quality, manufacturing and safety standards."
Although e-cigarettes do not produce smoke, their nicotine content has left some users worried as to whether their vapour may damage DNA and lead to tumours or other health problems.
Electronic vapour products (EVPs) are becoming an increasingly popular alternative to conventional tobacco cigarettes among smokers worldwide.
They are battery-powered devices that deliver vaporised nicotine and flavourings to users from an 'e-liquid.'
Mr Walele added : "In conclusion, the use of the e-cig for up to 2 years in this study appears to be an acceptable alternative for smokers, with the advantage of reducing the exposure to potentially harmful smoke constituents."
Last year Public Health England says the devices are '95 per cent safe' - and 'must be clearly positioned as products that help adult smokers to quit.
But recent research has also suggested teenagers who start smoking are up to two and a half times more likely to become regular smokers within a year.
