A physical dependence and a psychological addiction are two different things, and anyone with a substance abuse problem may have one or the other, or even both conditions at the same time. A physical dependence starts with a tolerance. The more that you use the substance in question the more your body can utilize at once, and it will take increasing amounts of the drug for you to experience the same effects as the last use. The cells in the body learn to function with the drug, and if the drug is discontinued then the body may suffer from physical withdrawal symptoms. The substance abuse has caused your body to depend on the substance, and when it is not available then your bodily and cellular functions are disrupted as a result. This can lead to cold sweats, shaking, nausea, and other physical withdrawal symptoms during the detox period.
A psychological addiction is somewhat different from a physical dependence, but both of these conditions can be present at the same time. A psychological addiction occurs in the brain, and the user feels that they must have the drug and will do almost anything to get it. Compulsive gamblers have a psychological addiction, and many drugs can also cause this problem even if they do not make the user physically dependent. This type of addiction can be more difficult to treat than a physical one, because detox will remove the substances from your system but it will not stop you from craving the substance on a psychological level.