How peer pressure may influence an individual?

Under the effect of peer pressure and the desire to be accepted, a person can engage in harmful behavior such as smoking or drug addiction. 

Under the effect of peer pressure, a person can lose their identity because of being forced to conform to rules that don't resonate with their personality.

A person might over-spend money on luxury items or brands just to get accepted by their peers or by their social group. 

As a person conforms to the rules set by others, they might lose the sense of their own self and might end up with low self-confidence.

Under the effect of peer pressure, a person can stick to the opinion of the group even if it's not right for them. For example, a person might choose a career that they don't like just because everyone is recommending it.

When a person doesn't work on fulfilling their own important needs then they might not experience happiness. Because people who do anything to get accepted by others ignore their own needs, they usually become unhappy.

Under the effect of peer pressure, many people feel compelled to get married at a certain age or when they discover that all of their friends are married. This type of thinking can lead to a wrong marriage partner choice. (See Why Beautiful Women Marry Less Attractive Men?)

Peer pressure can make a person less brave. If a person always chooses to stay in their comfort zone and to copy others then they might not have the chance to develop the courage needed to face life problems.

After making a decision influenced by peer pressure, the person will have to find a way to convince themselves that they took the right decision. Self-deception is a strategy people use to convince themselves that they did the right thing when they feel unhappy.

As a result of taking so many decisions because of peer pressure, a person will end up with the habit of following the herd regardless of what they believe in.

Many people keep their unwanted jobs, do what they hate and don't dare to make changes to their lives because of peer pressure. (See Why do people hide emotional pain?)

As a result of living the life others are dictating, a person who follows the herd usually ends up dissatisfied with their life.