According to the dictionary definition, dependency refers to a submissive, obedient state characterized by the loss of personal freedom.

Many people believe that their main goal in life is to live a pleasant, easy and active life, to achieve a "good" social status that satisfies their expectation and of those around them, and to control their life and psychological mental state.
A mixture of these goals can lead to dependency. A general rule says that if a behaviour is followed by a pleasant outcome, this behaviour will be repeated in the future.

From a psychological point of view,
dependency refers to an excessive, abnormal and harmful behavior.

It might sound unbelievable, but almost all human activities - such as working, feeding, sex, collecting valuable materials, taking pills, drinking alcohol , and taking drugs can turn into a dependency.

Once a person loses their freedom, their personality slowly and insidiously changes. A self-dilusional reality is created by the addict through lies and twisted explanations that protect the person from losing the their self-esteem and other peoples' respect, therefore stops the addict from becoming aware of these changes.

Many people do not like to be called substance dependents, because this term is perceived throught its negative connotation. Personal freedom, self-determination, self-control, being a efficient member of the society, and being healthy are few of the most valuable traits. As long as a person is dedicated to their personal pleasures and pasions without losing their health, social status, or the ability to work, they will not be classified as substance addicts. This term (substance addict) is only used when the values mentioned above are impaired, the person's life perspectives and interests narrow, and the addictive behaviour becomes dominant (without being followed by its initial satisfaction). Finally, tge person discovers that drinking offers no satisfaction. A similar situation is faced by an workoholic (a person who is works abusively) who continues to work excessively even when they have lost the interest on the work related results and success. The inner dynamic of dependency leads to a progressive incapacity to perceive pleasure and a general loss of life appetite.

There are two types of dependences: physical dependency and psychological dependency.

Physical dependency is caused by the constant, frequent and abusive consumption of harmful substances. The body adjusts to these substances causing an increased tolerance. In this state, the body needs the substance to function normally.
Physical dependency occurs when the addict stops using the substance, and is characterized bythe occurance of withdrawal syndrome (unpleasant physical symptoms). Therefore, the body will function normally only when the person returns to the use the substance.

We can talk about a psychological dependency when the person displays an inner desire and an obsessive need to consume the harmful substance in order to achieve pleasurable outcomes or to avoid discomfort.
A psychological dependent uses that substance to obtain a comfortable psychological state and to cope with stressful situation and low moods. When the addict cannot consume the substance, they experience uncomfortable feelings (even fear).

Psychohogical and physical dependency can develop independently.
Each individual that develops an addicted displays a typical, unhealthy and disfunctional emotional, cognitive, and behavioral patterns long before the actual onset of the dependency. When the dependency develops, decisive for it's onset is the person's need to use the substance in order to achieve certain pleasurable outcomes, and not the actual use of drugs.