Many factors determine how successful a person will be at quitting smoking, however, having a mental health condition such as depression can make it especially hard to kick the habit. New studies hope to shed some light on why.
Although smoking is now banned in most public venues and campaigns have largely been effective in raising awareness of its significant health risks, for many people, quitting smoking feels like a near impossible challenge. One of the key reasons why smoking is so addictive is that nicotine activates our brain’s reward pathways. When we are exposed to nicotine either via a cigarette, vape, nicotine patch, or nicotine gum, this stimulates the release of dopamine into these pathways, the neurotransmitter responsible for the feel-good sensations we experience from both natural (e.g., tasty food) or secondary (e.g., money) rewards. This release of dopamine generates the pleasurable “buzz” that many smokers recall experiencing when they smoked their first cigarette. It can also enhance sensations of pleasure and prolong the experience of pleasure. These sensations are what drives many people to become regular smokers.
Although nicotine is known to be an especially difficult substance to quit, conditions that affect a person’s sensitivity to rewards may determine how likely they are start smoking in the first place, and how difficult they may find it to stop. New research suggests that depression – a psychiatric condition often characterised by a reduced ability to experience pleasure – may do just this. Individuals with depression have been found to smoke at much higher rates than individuals who have never been depressed. Furthermore, quitting smoking often increases the risk for depression recurrence for individuals with a history of the condition. Importantly, depression has been found to be associated with reduced sensitivity to rewards and weaker activation in brain reward pathways in response to pleasurable events. Given that nicotine enhances reward sensitivity, one intriguing hypothesis is that individuals with depression may be more likely to smoke because smoking restores their ability to experience pleasure (even if only temporarily).
In a study conducted at Harvard Medical School’s McLean Hospital, we sought to test this hypothesis by having smokers and non-smokers, with and without a history of depression, play a computer game that required learning through trial-and-error which of two shapes was associated with a higher chance of winning a monetary reward. Prior studies in non-depressed individuals have found that people tend to bias their responses toward the shape that has the highest probability of paying, however, this bias is weakened or even absent in individuals with depression. The results of this study showed that compared to individuals who had never been depressed, individuals with a history of depression showed reduced reward sensitivity on the task. However, this was not the case for individuals with a history of depression who smoked. Instead, these individuals showed levels of reward sensitivity that were comparable to people who had never had depression before (see Figure 1 below).
Figure 1. Individuals with a history of depression showed reduced reward sensitivity relative to individuals without a history of depression, however, this was not the case for individuals with prior depression who smoked.
These findings suggest that the reductions in reward sensitivity that accompany depression may be reversed by smoking, and this may be what drives increased rates of smoking in people who are prone to depression.
There are several important implications of these findings. First, the results highlight a possible reason why individuals with current or past depression may be more likely to start smoking and find it more difficult to quit. If smoking restores a depressed person’s ability to experience pleasure and if quitting exacerbates depressive symptoms, it is not surprising why depression and smoking often go hand-in-hand. Second, the study raises the important notion that new medications that target the same pathways as nicotine, may be helpful in alleviating some of the symptoms of depression for people who have failed to respond to traditional antidepressant medications or psychotherapy. This is an exciting new prospect given that many of the treatment options available for depression often fail to improve symptoms characterised by loss of pleasure, even if they are more effective at targeting other features of depression, such as sad mood and negative thinking. Finally, the findings of this study highlight the importance of managing depressive symptoms when a person prone to depression tries to quit smoking. It is possible that a two-pronged approach focused on managing cravings as well as managing the mood symptoms that can accompany cravings, may be most effective in individuals with a history of depression who want to quit.