Although some narcotics like codeine and morphine are legal if prescribed for pain relief, heroin is an illegal narcotic because it has dangerous side effects and is very addictive.

Many people who are addicted to heroin inject the drug into a vein with needles, and may inject the drug several times a day. Over time, the needle marks, or tracks, can become permanent scars. 

Often, heroin addicts will share needles, which can lead to infection with dangerous germs like hepatitis B or C or HIV, the virus that causes AIDS.

Heroin is a very addictive drug and many people find it extremely difficult to stop using it — even after using it for just the first or second time. Heroin users constantly crave their next dose.

If heroin addicts suddenly try to stop using the drug or are unable to get another dose, they often develop withdrawal symptoms, like feelings of panic, sleeplessness, bad chills and sweats, muscle pain, stomach cramps, nausea, vomiting, and diarrhea.

Taking an overdose of heroin can cause a person to stop breathing and die.