Effects of Drugs on the Body Drug abuse is commonly defined as the harmful, non-medical use of a mind-altering drug. The constant misuse of such drugs can lead to poor health and to personality and behavioral problems. Some people use the term drug abuse of refer only to problems with illegal drugs. Other people include the harmful use of illegal drugs, even ones prescribed by a doctor. Cultural attitudes about a drug help determine whether its use is considered harmful. For example, both alcohol and marijuana can produce a similar form of intoxication. However, most people consider the moderate use of alco