How Addiction Actually Works
One mechanism, many substances
Most addictive substances and behaviours converge on the same underlying circuit: the brain's dopamine-driven reward and motivation system. In short — a substance triggers a dopamine spike well beyond an everyday reward like food or a conversation; repeated exposure causes the brain to dial down its own sensitivity in response (tolerance); and when the substance is removed, dopamine activity dips below baseline, producing the low mood, irritability, and craving of withdrawal. The full mechanism, including how long baseline sensitivity takes to recover, is covered in the Your Brain guide.
What This Guide Covers
What differs substance to substance is the speed and severity of that cycle: nicotine's tolerance builds within days, alcohol's withdrawal can be medically dangerous, caffeine's is a mild headache. The sections below cover those substance-specific timelines, along with the practical strategy the general mechanism alone doesn't tell you — what actually helps someone quit, how to recognise a developing problem, and how to get through a craving in the moment.
Why this framing matters
Addiction isn't a single, substance-specific phenomenon — it's a general property of the dopamine reward circuit responding to any sufficiently strong, sufficiently repeated stimulus. That's why the practical tools that help transfer across substances, even though the specific timelines and treatment options covered section by section differ substantially.