This is a hotly debated issue. Generally, when people speak of addiction, what they are referring to is a person’s continued use of a drug despite the fact that it is harmful to their health and their general ability to function adequately.
When someone has been taking an opiate on a regular basis, the brain adapts to this and changes its circuitry. When the opiate is no longer taken, inhibited neurons start functioning again. This causes an imbalance of chemicals in the brain, which interacts with the nervous system to produce classic withdrawal symptoms.
The reasons for the abuse of any type of drug are, according to the MRC.:
To alter mood states
To improve health
To cope with personal, social or interpersonal situations
For enjoyment, taste