The regular habit of intake of drugs leading to physical, mental and psychological dependence is called drug addiction.
It is the self-administration of drugs for non-medical reasons.
It is described as a state, psychic and also physical, resulting from the interaction between a living organism and a drug, shown by behavioural responses that always include a compulsion to take the drug on a regular basis to experience its psychic effects and avoid discomfort of its absence.
A person may show dependency on more than one drug.
Addiction is harmful for the individual because it leads to mental and physical degeneration and is also harmful for the society.