There's no success like failure...

From The British Medical Journal via Tobacco Analysis Blog via Freedom 2 Choose via Leg Iron:

Conclusions Available trials indicate that nicotine replacement therapy is an effective intervention in achieving sustained smoking abstinence for smokers who have no intention or are unable to attempt an abrupt quit. Most of the evidence, however, comes from trials with regular behavioural support and monitoring and it is unclear whether using nicotine replacement therapy without regular contact would be as effective.

[Skip a bit]

The results imply that compared with placebo twice* the number of smokers sustained six months’ abstinence as a result of nicotine replacement therapy. This equates to about an additional 3% of all smokers quitting who would otherwise not have done so**.

This is a similar effect size to treating smokers who are motivated to quit, where 4-5% might be expected to abstain for six months owing to use of nicotine replacement therapy. Previous data suggest that half of those who sustain six months of abstinence will maintain it for the rest of their lives.***

* The relative success compared to the placebo group is only of interest in deciding whether the treatment itself has any effect at all, and not whether that makes the treatment worthwhile. The use of the word "twice" suggests that nicotine replacement therapy is highly effective, but "twice" could mean that 0.1% of all smokers quit and 0.2% of all people using nicotine replacement therapy quite, for example.

** Of course that doesn't mean that 3% of smokers quit, it means that 3% more quit. Let's assume that five per cent of smokers quit for good every year x ten million smokers in the UK = 500,000 quitters. If the number of quitters goes up by 3%, then 515,000 smokers quit, those extra 15,000 quitters are only 0.15% of all smokers, for example.

*** But they tell us that only 2% or 3% of smokers who are "motivated to quit' actually quit long term. So out of ten million smokers in the UK, 250,000 give up permanently, so 3% x 250,000 = 7,500 = an additional 0.075%, call it a tenth of a per cent in round figures.

It appears that the NHS spends £74 million a year on stop smoking services. £74 million divided by those extra 7,500 quitters = nearly £10,000 per quitter.