Earlier this year, I quit cigarettes with the help of Pfizer’s new smoking cessation drug, Chantix. I was skeptical at first, because the advertised success rate is only 1 in 5. However, I was never the pack-a-day type, and a month on Chantix seemed to do the trick. Quitting came with some other lifestyle changes. For instance, it was hard for me to go to the bar and watch friends take frequent cigarette breaks, so I found myself avoiding these excursions. While I thought this change in behavior was a matter of convenience, a new study in PNAS suggests that Chantix may have played a role in my reduced alcohol consumption.
Pia Steensland and colleagues trained rats to self-administer 10% ethanol (your average wine is 12%) and measured how this behavior changed with exposure to varenicline, the active ingredient in Chantix. They found that varenicline reduced consumption in a manner similar to naltrexone, the best available pharmaceutical treatment for alcoholism. Unlike naltrexone, which also reduces sucrose consumption, varenicline selectively targets rewards associated with alcohol.
Varenicline binds to nicotinic acetylcholine receptors (nAChRs). It has the highest affinity for the alpha4beta2 subtype and actually blocks nicotine from binding to them. At the same time, it has a lower potency than nicotine, meaning that it stimulates the receptors to a smaller extent than nicotine. These properties make it a good smoking cessation aide because it blocks the rewarding effects of cigarettes while stimulating nAChRs at low levels to stave off withdrawal symptoms. Furthermore, the drug is well-tolerated in humans.
The recent findings are fascinating because they confirm an overlapping mechanism for alcohol and nicotine addiction. Scientists observe a high correlation between both vices, and now they are beginning to elucidate the biochemical basis of this co-morbidity. It turns out that ethanol is capable of directly activating alpha4beta2 nAChRs, and previous studies have shown that the broad spectrum nAChR antagonist mecamylamine reduces ethanol consumption in a manner similar to varenicline.
The current study is part of a larger movement toward drugs based off the action of nicotine. Medicines that act on nAChRs are currently being developed for such mental disorders as schizophrenia and Alzheimer’s.