Smokers slowly build up nicotine levels to a peak, rather than receiving a burst of the drug in their brain with each drag, according to researchers at the Duke University Medical Center.

Vertex News reported March 9 that researchers who used PET scans to track brain activity during smoking also found that nicotine took longer to reach the brains of addicted smokers, possibly because their smoking-damaged lungs worked less efficiently. Eventually, however, both addicted and non-addicted smokers had the same levels of nicotine in their brains.

The study was published online in the Proceedings of the National Academy of Sciences.