Gaps between neurons that neurontransmitters pass across helping communication.
Intake of drugs in quantities that are potentially damaging to physical/mental health.
When a person is physically dependent on a drug and they have to take increasing amounts to gain the same effect they did previously.
Taking the drug becomes routine for the person, so they have to maintain drug use to gain pleasure, making withdrawal difficult due to habit.
Change in neurochemistry in the brain which stubstitues normal functioning so the body requires the drug to make the person feel normal.
Unpleasant physical effects when drug isn't taken by physical dependent drug users. Eg vomiting/headaches.