Genes to blame for difficulty in quitting

A new study shows some smokers have a genetic factor which makes it more difficult to quit smoking.  Smokers who have an abundance of "mu opioid receptors" (MOR) in their brain, are more likely to relapse because their brains find nicotine more rewarding. PET scans were used to show that smokers with excess MOR's had different genetic factors than smokers with less MOR's.
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