Drug harms fall into two broad categories; those that affect you, and those that affect others. The personal ones include death, health problems (including mental health), accidents, addiction, relationship breakdown and legal trouble. Harms to other people include violence, financial problems, crime, and disruption of the family unit.
Risk becomes more serious with repeated use. For example, it can take only, “a few” uses of a drug to become addicted to it. One might conclude that trying to get away with taking drugs isn’t worth the risk. This might also apply to the most harmful drug of all; alcohol.