Heroin users become physically and psychologically dependent on the drug, and experience heroin withdrawal symptoms if they stop taking it. Heroin's effects last for approximately four to six hours. As a result, addicts must take the drug several times a day to prevent the appearance of withdrawal symptoms. The need to continue taking the drug to avoid withdrawal is an important factor in heroin's addictiveness.

There are three phases of heroin withdrawal. The first is acute heroin withdrawal, in which the heroin addict experiences the withdrawal syndrome. This phase peaks after about three days and ends after about five days. The second phase occurs over the next two weeks. During this period, the body re-learns the process of making the endorphins which the user’s body has been substituting with heroin. The third phase can take anywhere from a week to a couple of months. During this phase, the body stabilizes its endorphin production. It is only after the completion of phase three that the former addict really feels good. However, it is the first phase that is the hardest to get through because the pain is so intense.

The primary symptoms of heroin withdrawal are:

• Abdominal cramps
• Depression
• Diarrhea
• Insomnia
• Nausea
• Vomiting

The most commonly experienced secondary symptoms of heroin withdrawal are: 

• "Goose Bumps”: Having goose bumps led to the origin of the phrase "quitting cold turkey."
• Alternating sweating and chills
• Anxiety
• Dehydration
• Dilated pupils
• Fever
• Gagging
• General body aches
• Hot flashes
• Hyperactivity
• Increased blood pressure
• Increased heart rate
• Irritability
• Leg cramps: Muscles that have been relaxed by the drug tighten and twitch, causing severe pain and uncontrolled, reflexive motion ("kicking the habit").
• Nervousness
• Perspiration
• Restlessness
• Watery eyes
• Weight loss

The horrible physical symptoms of heroin withdrawal are not the worst aspect of opiate addiction. The addict experiences psychological CRAVINGS that are very intense and become nearly impossible to fight. To quote Alfred Lubrano of the Knight Ridder/Tribune News Service: "The smell of burned matches, the sight of a $10 bill (the price for a 'dime bag' of drugs), even those 'Just Say No' anti-drug posters with a crossed-out needle, all act as potent cues that could bring even long-clean addicts to their knees, screaming for dope." Scientists have actually shown recovering addicts films of drug abuse while monitoring the drug users' brain activity. The results: Watching someone else use drugs, even on a film, spurs activity in the parts of the brain that govern motivation and craving.