Since 2001 the number of young people using illegal drugs has dropped by 900,000 to about 2.7 million. This drop is an important development for all the obvious reasons, plus one. Substance abuse is a disease. Until recently, we failed to grasp the nature of this disease and how to reduce the suffering it causes.

For decades, we did not want to believe that alcohol or drugs could have the power to take over our lives, despite the evidence we witnessed when our loved ones grappled with drug addiction. We did not understand...