People start drinking alcohol for reasons such as:
Pleasure
To be sociable
To feel relaxed
To forget worries
Out of the ten people who start drinking for such harmless reasons, two become physically dependent on and mentally addicted to alcohol.
Their body becomes so much accustomed to the use of alcohol over a period of time, that when they stop drinking, “withdrawal symptoms”, such as sleeplessness, anxiety, nervousness, tremors, convulsions, hallucinations etc. occur. This state is called Physical Dependence.
Alcohol becomes so central to their thoughts, emotions and activities that they cannot control the craving for drink. This state is called Psychological Dependence.
(Source: Webhealthcentre.com)