alcohol
Nicotine, by a very wide margin.
Nicotine is the most abused substance and its use causes the most diseases and deaths.
The most commonly abused prescription drugs are: narcotics, anxiolytics like Valium/Ativan/Xanax, and amphetamines. Any controlled substance has the potential for abuse as well as psychological and/or physiological addiction.
By a substantial margin, alcohol is the most widely abused drug in every age group—including children. However, marijuana is the most widely used illicit substance among all age groups, but “club” drug use is increasing.
Alcohol.
indicators show that hydrocodone is the most commonly abused narcotic analgesic
Meth
alcohol
Sugar
ANY substance that is being abused can be an addiction.
Tobacco
Nicotine and/or caffeine