The pursuit of drugs is universal and inescapable, irrespective of time or species and in the private lives of popes and presidents, crooks and ordinary citizens alike. The struggle between this natural drive and societal law has become a deadly war that can never be won. But there is an answer, the lessons learned from animals show that we can make peace with the fourth drive, understand that drugs are a kind of medication needed to change how we feel, and use our human privileges of technology and education to design safe intoxicants. This book addresses the ageless question of why we seek drugs. Siegel, a renowned psychopharmacologist, explains his controversial theory of the fourth drive - a drive as powerful as hunger, thirst and sex - the desire for intoxication.