The highly addictive substance nicotine found naturally in tobacco has many effects on the brain. When a person smokes the nicotine found in cigarettes alters the chemicals in brain very quickly. This causes changes to your mood and concentration levels and also produces feelings of pleasure and reduces stress and anxiety.

These mood changes are one of the main factors that cause people to become addicted to smoking. In addition to this, the more you smoke the more your brain gets used to nicotine; meaning you need to smoke a greater number of cigarettes to reach the same effect.

Recent studies show that due to these effects, most people that try cigarettes only once or twice go on to become addicted. You can read a full article by the BBC here:

http://www.bbc.co.uk/news/health-42619664