Now, a team of University of Michigan scientists is reporting new evidence of why that might be: Smoking produces major changes in the flow of "feel good" chemicals between brain cells, both temporarily and long-term. And those changes in flow match up with changes in how smokers say they feel before and after smoking.
It's the first time smoking has been shown to affect the human brain's natural system of chemicals called endogenous opioids, which are known to play a role in quelling painful sensations, heightening positive emotions, and creating a sense of reward. It's the same system that is stimulated by heroin and morphine.
The research team, from the U-M Medical School, will present the results Tuesday afternoon in a lecture at the annual meeting of the Society for Neuroscience.
The new results come from a pilot study involving a small group of young male pack-a-day smokers and non-smoking comparison subjects. Despite their study's small size, the researchers say the surprisingly large effect on opioid levels they found suggests a promising road for further discovery. That may lead to better understanding of why smoking affects people the way it does -- including the mystery of why it's often so hard to quit, despite tobacco's many health dangers.
"It appears that smokers have an altered opioid flow all the time, when compared with non-smokers, and that smoking a cigarette further alters that flow by 20 to 30 percent in regions of the brain important to emotions and craving," says David J. Scott, a graduate student in the U-M Neuroscience Program who will present the results. "This change in flow as seen on a brain scan correlated with changes in how the smokers themselves reported feeling before and after smoking."