For decades, cigarette makers have been marketing the so-called light cigarettes - which contain less nicotine than regular smokes - with the implication that they are less harmful to smokers'' health, however, the new study from University of California, Los Angeles challenges the notion.
Light cigarettes have nicotine levels of 0.6 to 1 milligrams, while regular cigarettes contain between 1.2 and 1.4 milligrams.
The research team led by UCLA psychiatry professor Dr. Arthur L. Brody have found that low-nicotine cigarettes act similarly to regular cigarettes, occupying a significant percentage of the brain's nicotine receptors.
They also looked at de-nicotinized cigarettes, which contain only a trace amount of nicotine (0.05 milligrams) and are currently being tested as an adjunct to standard smoking-cessation treatments.
They found that even that low a nicotine level is enough to occupy a sizeable percentage of receptors.
"The two take-home messages are that very little nicotine is needed to occupy a substantial portion of brain nicotine receptors and cigarettes with less nicotine than regular cigarettes, such as ''light'' cigarettes, still occupy most brain nicotine receptors," said Brody.
"Thus, low-nicotine cigarettes function almost the same as regular cigarettes in terms of brain nicotine-receptor occupancy.
"It also showed us that de-nicotinized cigarettes still deliver a considerable amount of nicotine to the brain.
"It can cause specific neurons to communicate and thus increases dopamine for an extended period of time.
"Most scientists believe that's one key reason why nicotine is so addictive," he added.
During the study, fifteen smokers were given positron emission tomography (PET) scans, a brain-imaging technique that uses minute amounts of radiation-emitting substances to tag specific molecules.
In this case, the tracer was designed to bind to the nicotine receptors in the brain.
The researchers could then measure what percentage of the tracer was displaced by nicotine when the research subjects smoked.
The data showed that smoking a de-nicotinized cigarette and a low-nicotine cigarette occupied 26 percent and 79 percent of the receptors, respectively, which was very close to what the researchers had originally estimated.
"Given the consistency of findings between our previous study with regular cigarettes and the present study - that showed us that inhaling nicotine during smoking is solely responsible for occupancy of brain nicotine receptors," said Brody.
The study appears in online edition of the International Journal of Neuropsychopharmacology.