Cigarette smoking may have effects on the human brain similar to those of antidepressant drugs, and this may explain the high rate of smoking among depressed people and their resistance to quitting.

Researchers have noted previously that depressed people are more likely to smoke and are more resistant to quitting. However, it was unclear if nicotine or other chemicals taken in during smoking directly affected the brains of people who were depressed.

In a new study Dr Gregory Ordway, professor of …