Well known for their medical use of relieving severe pain, narcotics are commonly abused drugs because of their euphoric effect and highly addictive quality. Most of the drugs in this category are administered orally or through intramuscular injection, and can be legally obtained under medical supervision. But narcotics such as heroin, opium, morphine, and codeine are frequently sold on the illicit market to addicts. (Not as well known are the narcotics hydromorphone, meperidine, and methadone.)

When narcotics are regularly used, the body eventually demands more of the drug in order to achieve the same high, which is known as developing a drug tolerance. Withdrawal symptoms such as watery eyes, runny nose, yawning and perspiration will develop only six to eight hours following the last use of the drug. Within 48 to 72 hours, more severe withdrawal symptoms may develop, including restlessness, irritability, appetite loss, tremors, stomach cramps, diarrhea, and chills alternating with excessive sweating. It may take one to two weeks for the body to return to "normal."