Nutt et al.’s experts ranked heroin as the most addictive drug, giving it a score of 3 out of a maximum score of 3. Heroin is an opiate that causes the level of dopamine in the brain’s reward system to increase by up to 200% in experimental animals. In addition to being arguably the most addictive drug, heroin is dangerous, too, because the dose that can cause death is only five times greater than the dose required for a high.
Heroin also has been rated as the second most harmful drug in terms of damage to both users and to society. The market for illegal opiates, including heroin, was estimated to be $68 billion worldwide in 2009.