Can you please define drug addiction?

Psychiatric Disorder. Drug addiction is defined as the use of prescription or illegal drugs for reasons other than their intended use, causing impairment in one's ability to work, to engage in meaningful relationships, and to enjoy life. Addiction usually leads to dependence and tolerance making it very difficult to stop. There are many different forms of treatment. Your pmd can provide you with resources.
Brain disease. A pathway deep in your brain is associated with necessary behaviors like eating, breathing, etc. When this pathway is triggered, a signal goes to another part of your brain that says "i like that." ie, breathing is necessary so humans "like" breathing. In addiction the drug takes over these pathways, and convinces you the drug is necessary & pleasureable, despite all the evidence to the contrary.
Temprory altof brain. Historically, addiction has been defined as physical and psychological dependence on psychoactive substances (for example alcohol, tobacco, heroin, caffeine and other drugs) which cross the blood-brain barrier once ingested, temporarily altering the chemical milieu of the brain.