New research shows that how fast a smoker breaks down nicotine could provide a guide in working out how best to quit.

How quickly a smoker breaks down nicotine is a guide to which therapy is best for kicking the habit.

Authors of new research say most smokers who try to give up tobacco fail within the first week, so matching them to the best treatment is essential.

Previous research has found a link between tobacco craving and levels of an enzyme called CYP2A6 which breaks down nicotine.

The faster the nicotine is metabolised, the likelier it is that the smoker will want to light up again soon, and the harder it will be to quit.

Scientists in the US and Canada used a biomarker - the speed at which CYP2A6 does its job - to see whether nicotine patches or a non-nicotine replacement drug called hantix or Champix) were more effective.

Smokers who broke down nicotine quickly - most smokers, in fact - were twice as likely to quit if they used varenicline than if they used patches, they found.

They also had a better chance of staying of tobacco six months later.

Slower metabolisers found nicotine patches to be as effective as varenicline, but without that drug's side effects.

The studies covered 1,246 smokers who wanted to quit, divided roughly equally into fast and slow metabolisers.

The smokers were randomly assigned to an 11-week course that comprised either a nicotine patch plus a dummy pill, varenicline plus a dummy patch or a dummy patch and a dummy pill.

The study did not cover electronic cigarettes, which some advocates say are a useful tool for giving up smoking.

The study appears in the journal The Lancet Respiratory Medicine.