The misuse and abuse of, and overindulgence in drugs have become a common occurrence in all age groups but more prevalent in adolescents and adults.
Some become addicted to certain drugs unconsciously and some consciously. To abuse a drug simply means to use a drug for non-medical purposes.
For example, taking a drug only for the effect it produces is an outright abuse of such drug and it eventually leads to addiction with time.
One however can become addicted unknowingly by administering such drug without resultant cure for the intended illness.