Addiction or substance abuse is a complex brain disease. There are two components to addiction, one is physical and the other is psychological factor. Addictive substances or behaviors change the reward circuits in the brain. The following are the factors that are responsible for developing addictions in an individual:

Genetics:
Genetic susceptibilities in individual play an important role in drug addiction. Some addictions like alcohol may be inherited. Individuals from families with a history of any kind of addiction are more likely to develop some other form of addiction.

Abuse:
Individuals who experience sexual, psychological, emotional or physical abuse are more likely to become addicts. These addictions become coping mechanism for dealing with strong negative emotions surrounding the abuse.

Environment:
Environment surrounding an individual also plays an important role in developing addiction. For example, children raised by addicted parents are more likely to view substance abuse and make the child to get addicted.

Substance:
Certain substances are more addictive than others, and the risk of getting addicted to substances like drugs such as cocaine, heroin, or methamphetamine is high when compared to other substances because of their ability to create dependence after relatively few uses.

Emotional Disorders:
Certain emotional disorders like anxiety, depression and bipolar depression etc. increase the risk of substance abuse and addictive behaviors. The individuals experiencing above conditions opt for drugs, alcohol, food, exercise, or work as a way to self medicate and escape the symptoms.

Low Frustration Tolerance:
Some individuals have a low frustration tolerance and they become easily upset over everyday stress factors and get addicted to the drugs.

All the above factors, play a role in addiction. One needs to control the above said factors in order to prevent drug addiction.