The Neurobiology of Tobacco Addiction – Part I

Blog Post created by dr_hays on Sep 11, 2015

In the comments of a previous blog, The Key to Stopping Smoking, I briefly discussed the impact tobacco addiction has on the brain.  Setting aside the equally important behaviorally side of tobacco dependence – automatic responses to triggers, habits, emotions – there are three primary factors that influence the addictiveness of tobacco.  I will focus today’s blog on the first factor – genetics.

There are several known genes that influence how our brains respond to tobacco and can make a person more susceptible to tobacco dependence.  More specifically, these genes influence the number of receptors that respond to nicotine (1).  For those who are genetically prone toward tobacco dependence, ongoing exposure to high levels of nicotine desensitize these receptors to the drug’s effects and can lead to the growth of many more– all of which crave nicotine.   The quick growth of receptors overwhelms the reward center in our brains and is largely responsible for the cravings and withdrawal symptoms we experience when trying to quit. 

Here is one way to think about it. 

When we are hungry for food, our body sends us signals that we need to eat.  Some signs include hunger pangs, mood changes, or light-headedness.  When we eat, these symptoms go away and we experience relief (and pleasure if it is something tasty).  Each of the nicotine receptors in our brain act like little stomachs, but the only thing that will satisfy or “feed” them is nicotine.  When a person does not smoke for several hours, nicotine levels start to drop.  At a certain point, the nicotine receptor will start sending unpleasant “hunger” signals to the body that intensify with time until they are provided with more nicotine.  With smoking, we call these hunger signals cravings and withdrawal.  Many people feel intense cravings when they awaken in the morning as their receptors have gone 6-8 hours without nicotine and are very hungry.  For some of my patients, this requires smoking more cigarettes in the first hours after waking to relieve cravings and withdrawal.  The continued presence and demands of many nicotine receptors can keep us stuck in a daily cycle of tobacco use which makes it difficult to quit. 

However, there is good news!  When a person stops using tobacco (like many of you have done here on Ex), these receptors start to go away.  Research shows that after 6-12 weeks, a person's brain starts to resemble that of a non-smoker, though there can be variation between individuals (2).  It is for this reason that stop smoking medications are often recommended - they can relieve cravings and withdrawal symptoms when a person is trying to quit.  The less time a person has to struggle through intense cravings, the more time they can commit to changing old behaviors, developing coping skills, and creating a new, smoke-free life. 

Here is a Mayo Clinic Youtube video that helps explain why it can be hard to stop smoking

I will plan to address the other factors that impact the neurobiology of tobacco addiction next week – the free-basing of nicotine and speed of delivery.  Until then feel free to share any thoughts, questions, or experiences in the comments below!

Added References:

1. Davies GE, Soundy TJ. The genetics of smoking and nicotine addiction. S D Med. 2009;(Spec No):43–49

2. Cosgrove, K.P., et al. β2-nicotinic acetylcholine receptor availability during acute and prolonged abstinence from tobacco smoking. Archives of General Psychiatry 66(6): 666-676, 2009.