Drug dependence is a medical term that refers to the state of needing a certain drug in order to function normally. When the drug is taken away, the person experiences distressing symptoms. Drug dependence is not always about using illegal drugs. For example, a diabetic can become dependent on the drug insulin. Without this drug, this person would die. Drug dependence is different than addiction or drug abuse, although people commonly use all three terms interchangeably. Addiction always refers to a physical state of chemical reliance on a drug to feel normal. A person addicted to alcohol or sedatives will undergo a physical withdrawal syndrome with symptoms such as delirium, tremors, sweats, and so forth, once the drug is taken away from him. A person can be dependent on a drug without being physically addicted to it. In other words, he has a psychological but not a physical dependency. The person may experience mental distress, a sense of loss or even depression when his drug is not available, but this is not the same as going through a physical withdrawal syndrome.