An addiction is literally the compulsive need for a substance, an activity, a food, a person, etc. It is the obsessive and habitual physiological and emotional reliance on a specific thing to fulfill a "hunger" within you. It comes in many forms, but most commonly, we associate addictions with substances like alcohol, methamphetamine, cocaine, heroin and other drugs. For example, my guess is that many of you have some level of addiction to your iPhones and iPads, etc. Why? Because you can't get along without them and you have a need to stay connected to your friends, family, etc. These communication devices are extremely addictive. But not necessarily damaging to you in the way a substance addiction is.
I know that many of you have heard it before, but just for the record anything that you compulsively need in order to function is bad for you and can potentially hurt or even kill you. But most especially this applies to drugs and alcohol. The severity with which drugs and alcohol can affect your life is huge. The damage to your brain is irrevocable. It cannot be undone. Withdrawal from an addiction of course depends on what you are addicted to, but most of us associate it with drugs. The symptoms of withdrawal from drugs are both physical and psychological and can range from feeling like you have snakes crawling all over your body to the sweats to hallucinations and insomnia. Depending upon the substance it can take days or weeks to withdraw from a drug.
Withdrawal from food or sex takes on physical and psychological characteristics as well because you may become anxious, stressed, depressed and irritable. This process may also take days or weeks depending upon the strength of your addiction. Again, the severity of the addiction determines the severity of the withdrawal. And if it's bad, it could lead to suicide. The important things is first, don't become addicted to anything! But if you do, please seek help. You cannot go through withdrawal without help.