Because they see it modelled by others
Environmental factors, such as the influence of parents or older people, play a role in initial alcohol use. For example, parents who drink regularly and who view drinking favourably may have children who do the same.
As part of normal developmental transitions
Adolescents who are in the process of puberty may drink alcohol as part of the dramatic physical, emotional and social change of adolescence. In other words, drinking is a part of self-exploration, especially if their peers are also beginning to drink. Likewise, young people in college or university may drink alcohol during this time of transition to adulthood in order to explore their own values and beliefs about alcohol.
To relieve stress
Some new drinkers may use alcohol as a way to escape or cope with problems. Alcohol may temporarily relieve stress and focus attention elsewhere, but the problems remain well after they stop drinking.