Image copyright Thinkstock Image caption Although smoking is becoming less popular in many parts of the world, the total number of smokers is growing

A blood test could help people choose a stop-smoking strategy that would give them the best chance of quitting, research in a Lancet journal suggests.

Studies show as many as 60% of people who try to give up start smoking again in the first week.

But researchers argue measuring how quickly a person breaks down nicotine could boost the chances of success.

Other experts say the cost-effectiveness of these extra tests would need to be assessed.

Patches or pills

Nicotine is one of the most addictive substances in cigarettes - smokers crave more nicotine when their body's levels drop, prompting them to smoke again.

But different people break down nicotine at different rates.

Some scientists suggest people who break it down more quickly may crave more cigarettes and in turn find it harder to quit.

In this study, researchers from the University of Pennsylvania in the US enlisted some 1,240 people on different smoking cessation programmes.

They checked each volunteer's blood to see if nicotine was broken down at a normal or slow rate.

Volunteers received either a nicotine patch, a drug called varenicline or treatment with a dummy pill.

Varenicline is a non-nicotine based drug that is available on prescription . Doctors balance potential side-effects - including the risk of depression and suicide - against the harms of continued smoking.

Everyone in the trial had access to behavioural counselling too.

Image copyright SPL Image caption Nicotine replacement can be in the form of patches and sprays

Scientists found people who broke down nicotine at a normal rate had a better chance of quitting while using varenicline than those using nicotine replacement patches.

Though volunteers who broke nicotine down more slowly had similar success rates whichever method they used, they reported more side-effects with the varenicline.

Prof Caryn Lerman, one of the lead researchers, said: "If these tests are used, people could have a sizeable chance of success.

Wider use

"For some people, with normal metabolism of nicotine, the chance of success might be low on the patches but could double if they take the pill while for a third of the population with slower breakdown, cheaper patches might be best."

Blood tests to check for nicotine breakdown speed are currently used in research but scientists say they could be easily developed for much wider use.

Dr Neil Davies, of the University of Bristol, provided an independent comment: "The results are an important scientific advance.

"If the findings can be replicated they could lead to changes in practice. But there are still questions that need to be answered.

"The cost-effectiveness of these tests would need to be taken into account."

Prof Robert West, from University College London, who was not involved in this paper, said: "We know that if people try to quit unaided their chance of success for a year is about 4%.

"The way to succeed is to keep trying. It is like rolling a dice. If you keep rolling it you will succeed but if you stop rolling you will fail."

The University of Pennsylvania research was published in the the Lancet Respiratory Medicine journal.