Smokers who are unable to quit should instead be encouraged to cut down, according to new advice from a health watchdog.
The National Institute for Health and Clinical Excellence - Nice - recommends that doctors prescribe nicotine gum and patches, even if patients only want to reduce the number of cigarettes they smoke.
The guidelines, which doctors will be expected to follow, say giving up tobacco entirely is the best for health, but if that is not possible then cutting back on cigarettes does reduce the harm from tobacco.
Nice also endorses increasingly popular electronic cigarettes, which contain nicotine rather than tobacco. E-cigarettes do not have a medical licence and cannot be prescribed on the NHS.
The body says their "effectiveness, safety and quality can't be assured", but doctors should "advise that these products are likely to be less harmful than cigarettes".
Professor Mike Kelly, director of Nice's Centre of Public Health, said smokers who try to cut down without using nicotine replacement products are unlikely to gain a health benefit because they tend to inhale more deeply.
"Tobacco is highly addictive, which is why people find it so difficult to stop smoking," he said. "Put simply, people smoke for the nicotine, but die because of the tar in tobacco."
Professor John Britton, chair of the Royal College of Physicians' tobacco advisory group, welcomed the new guidance.
"Smokers smoke for nicotine, and since tobacco smoke is by far the most harmful available source of nicotine, switching to alternatives as a short or long-term substitute is the obvious healthier choice," he said.
"This guidance has the potential to change millions of lives for the better."
Martin Dockrell, director of policy and research at the stop-smoking group Ash, said cutting down on cigarettes can be an important step to giving up.
He said: "We would recommend using licensed nicotine replacement therapies such as patches, gum or sprays because their safety and reliability is proven.
"But if smokers are using unlicensed e-cigarettes, they are still a much less harmful alternative to smoking."