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Scientists Discover Why Quitting Smoking Can Cause Temporary Depression

Canadian scientists say that very heavy smokers who quit smoking can experience a spike in an enzyme called MAO-A. MAO-A metabolizes serotonin and so too much MAO-A can result in too little serotonin and feelings of sadness and depression.

Heavy smokers who quit their habit sometimes experience feelings of sadness that closely mimic the feelings of clinical depression. This can make maintaining abstinence from cigarettes much harder than it would otherwise be and may in part explain why about 50% of people who quit smoking relapse back to tobacco within three days of stopping use.

Researchers at Canada’s Centre for Addiction and Mental Health (CAMH) say they think they’ve figured out why quitting smoking can make some people feel so sad.

Dopamine is the body’s major feel-good neurotransmitter, and most studies which have examined tobacco’s effects on mood and pleasure have centered around this chemical. Researchers at CAMH, however, examined the effects of tobacco use cessation on an enzyme in the brain called MAO-A, which is an enzyme that metabolizes (removes) excesses of another feel-good chemical, serotonin, from the brain.

The researchers found that very heavy smokers who quit smoking developed an acute spike in MAO-A levels in the brain which caused a corresponding dip in serotonin levels and thus, feelings of depression.

Why Does This Happen?

The scientists believe that decreased levels of a chemical called harman in the body result in the MAO-A spike. Harman is a chemical that is formed and consumed when tryptophan in cigarettes is burned and then inhaled. When people stop smoking, harman levels in the body fall and this seems to lead to a spike in MAO-A levels.

Only Very Heavy Smokers Are Affected

  • In clinical tests, people who smoked more than 25 cigarettes per day saw MAO-A levels rise by 25% upon quitting.
  • People who smoked between 14 and 25 cigarettes per day saw no appreciable rise in MAO-A levels.

Why Is This Significant?

The researchers say that understanding how and why quitting smoking leads to feelings of depressions may lead to interventions that would make giving up the habit a little bit easier.

Suggested interventions include giving recently quit smokers an anti depressant called Moclobemide or improving cigarette filters so they do a better job of removing harman from cigarette smoke that is inhaled into the body.

The full study results can be examined in the August edition of Archives of General Psychiatry.

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