Bupropion and varenicline are standard treatment for smokers looking to quit but researchers have so far been unable to determine exactly how they work.
Using brain imaging, researchers from the University of California in Los Angeles found patients treated with bupropion or varenicline had reduced activity in parts of the brain known to be associated with smoking-related cravings. It is hoped the findings will improve understanding of such cravings and how treatment can be improved.
In one study, researchers assessed changes in brain activation in response to smoking cues among 30 smokers.
Participants were randomly assigned to take either bupropion or placebo for eight weeks. They underwent functional MRI scans within one week of joining the study and again after eight weeks after the treatment period ended.
During the scans, participants were shown short videos containing either smoking cues or neutral cues, which acted as controls. They were then asked to report how strongly they craved cigarettes after watching the video.
Participants treated with bupropion had fewer cravings in response to smoking cues than those who watched the placebo video.
The brains of the bupropion group showed reduced activation in areas of the brain known to be associated with cravings, including limbic and prefrontal regions.
Activation in these brain regions was consistently lower among those with fewer cravings regardless of whether they received treatment or placebo.
Authors concluded: ‘These results demonstrate that treatment with bupropion is associated with an improved ability to resist cue-induced craving and a reduction in cue-induced activation of limbic and prefrontal brain regions.’
Meanwhile, a second similar study of 22 patients also found those treated with varenicline experienced a reduction in both brain activity and reported cravings in response to smoking cues.