Definition: An addiction occurs when you cannot permanently stop yourself from doing something even though it is harmful to you. Usually the things we become addicted to act directly upon the brain and body to produce a desirable alteration in how we think or feel. Common addictions are to tobacco products, drugs, alcohol, gambling, pornography. When we speak of addiction we often use terms like "tolerance" and "withdrawal". Tolerance occurs when it takes more and more of the substance to get the same amount of pleasure. Withdrawal occurs when you experience painful, and sometimes dangerous, symptoms when you go for any period without that substance. An addiction can be psychological, physical, or both.