A new review has cast doubt on the safety of e-cigarettes and their use as a smoking cessation aid.

However, the report from the Center for Tobacco Research and Education in California, says in cases where other smoking cessation methods have failed, doctors should support patients who wish to use e-cigarettes to quit smoking in these circumstances.

The review of research to date on e-cigarettes says while data are limited, it is clear that e-cigarette emissions are not merely 'harmless water vapour' and can be a source of indoor air pollution.

It says it is reasonable so assume that, if existing smokers switched completely from conventional cigarettes, with no other changes in use patterns, there would be a lower disease burden caused by nicotine addiction.

However, the review said the current evidence, although limited, pointed to high levels of dual e-cigarette and conventional cigarette use, no proven cessation benefits, and rapidly increasing youth initiation with e-cigarettes.

"Although some cite a desire to quit smoking by using the e-cigarette, other common reasons for using the products are to circumvent smoke-free laws and to cut down on conventional cigarettes, which may reinforce dual use patterns and delay or deter quitting."

The review, published online in the journal Circulation, points out that studies among youth find that as many as one third of young people who use e-cigarettes have never smoked a conventional cigarette.

It ways nicotine is a highly addictive substance with negative effects on animal and human brain development, and this development is ongoing in adolescence.

The report says high rates of dual use of both type of cigarette may result in a greater total public health burden and possibly increased individual risk if a smoker maintains an even low-level tobacco cigarette addiction for many years instead of quitting.

It says 100% smoke-free policies have a bigger effect on smoking prevalence, as well as hospital admissions for heart disease than weaker policies, such as allowing e-cigarette smoking.

"Introducing e-cigarettes into clean air environments may result in population harm if use if the product reinforces the act of smoking as socially acceptable or if use undermines the benefits of smoke-free policies."

The review says doctors should tell patients the safest and most proven quit-smoking drug therapies are nicotine replacement medications Champix and Zyban. Referrals to quit smoking free phone lines or other counselling support enhances the effectiveness of these medications, the review says.

The report says if other smoking cessation therapy has not worked on a patient, or if the patient refuses to employ this therapy, and wants to use e-cigarettes to try to quit smoking, it is reasonable to support the attempt.

However, it says patients should be informed that while the e-cigarette aerosol is likely to be much less toxic than cigarette smoking, the products are unregulated, contain toxic chemicals and have not been proven as cessation devices.

The report says the patient should be advised not to use e-cigarettes indoors or around children, as bystanders may be exposed to nicotine and other toxins, at levels much lower than cigarettes, through passive exposure to the e-cigarette aerosol.

It says as there are no long-term safety studies of the use of the new product, patients should be urged to set a quit date for e-cigarette use and not plan to use the product indefinitely.

Patients should also be advised to quit smoking tobacco cigarettes entirely as soon as possible, as continued cigarette use, even at reduced levels can impose health risks, particularly for heart disease.

The report says there is currently no evidence that cigarette companies are acquiring or producing e-cigarettes as a strategy to phase out regular cigarettes.

One of the three authors of the review article, in the 'disclosures section', is a consultant to several pharmaceutical companies that market smoking cessation medications and has been a paid expert witness in litigation against tobacco companies.

Only one in two says HSE right on e-cig ban