Question: What is (are) Prescription and Illicit Drug Abuse ?
Answer: Physical dependence is a normal process that can happen to anyone taking a medication for a long time. It means that the body (including the brain) is adapting to the presence of the drug, and the person may require a higher dosage or a different medication to get relief; this condition is known as tolerance. They may also suffer from withdrawal or feel sick when they stop taking the medication abruptly. However, the symptoms of withdrawal can usually be prevented or managed by a physician, which is why it is so important to talk to a doctor before stopping a medication. Someone who is addicted to a drug may also be physically dependent on it, but rather than benefitting from the drugs effects, an addicted person will continue to get worse with continued or increasing drug abuse. An addicted person compulsively seeks and abuses drugs, despite their negative consequences.
Source: NIHSeniorHealth

Question: What are the symptoms of Prescription and Illicit Drug Abuse ?
Answer: Not always. Some warning signs, such as sleep problems, falls, mood swings, anxiety, depression, and memory problems -- can also be signs of other health conditions. As a result, doctors and family members often do not realize that an older person has a drug problem, and people may not get the help they need.
Source: NIHSeniorHealth