Electronic cigarettes vary enormously in how big a nicotine hit they give to users, which is thought to be a factor behind the low rate of quitting tobacco smoking in an Auckland University trial.
The kind of Elusion e-cigarette used in the trial delivers 19 micrograms of nicotine per puff. This is less than 40 per cent of the nicotine from the Green Smoke brand, and less than 20 per cent of the hit of a tobacco cigarette, according to the results of mechanical tests by Christchurch researcher Dr Murray Laugesen and his colleagues on e-cigarettes available from New Zealand shops or the internet.
They also found only low levels of toxins were produced by the e-cigarettes, many times less than in the smoke from real cigarettes.
E-cigarettes have developed rapidly since their emergence a decade ago and are fast growing in popularity. The battery-powered devices look not unlike real cigarettes, but produce a nicotine vapour rather than smoke.
Dr Laugesen told the Herald future quit-smoking trials would now want to focus on e-cigarettes that delivered the higher amounts of nicotine because they might produce greater quit rates.
"Stronger brands and legalisation of sale could reasonably be expected to improve results considerably."
Quit rates in the trial of 657 smokers were much lower than anticipated, the researchers, including Dr Laugesen, wrote in the Lancet medical journal. They concluded that e-cigarettes, with or without nicotine, were about equally effective as nicotine patches at helping smokers to quit tobacco and stay off it for six months.
On other measures, however, the trial found that e-cigarettes containing nicotine were superior to patches - the median time to returning to smoking was more than twice as long; addiction and withdrawal effects were not as bad; and tobacco usage was lower.
Dr Laugesen said the greater reduction in addiction scores could be expected to lead to more success when the nicotine e-cigarette users next tried to quit tobacco.
The refillable or cartridge e-cigarettes in the bench tests ranged in start-up and running costs for the first 90 days - with one refill a day - from $3.24 to $6.97 a day. The factory-made tobacco cigarettes cost $8.40 for 12. Twelve cigarettes a day delivered 19.2mg of nicotine and one cartridge in the Elusion just 4mg, while one fill of the newer Elusion Ego refillable supplied 11.3mg.
Some public health researchers argue they will keep people smoking long-term while others think they aid quitting.
Nicotine per puff
100 micrograms - Tobacco cigarette
49mg - Green Smoke
45mg - Elusion Ego
40mg - Liberty disposable
35mg - EasyPuff
31mg - Liberro
23mg - Mirage Goldstar
20mg - Republic Union
20mg - Blu ecig
19mg - Elusion