Tolerance, dependence and addiction are three separate conditions that can be linked to the use of certain over-the-counter and prescription drugs. Although they often are mistakenly confused with one other, each condition has distinct characteristics, including:

• Tolerance. Occurs in patients who use certain medications over a long period of time and find that larger amounts of the drug are required to obtain the same effect achieved at the initial dosage.
  
  
• Physical dependence. Occurs in patients whose bodies adapt to using a drug. Patients who become physically dependent upon a drug will suffer symptoms of withdrawal if their bodies are suddenly deprived of the medication.
  
  
• Addiction. A primary physical and psychological disease. It is characterized by harmful and compulsive use of a drug that results in repeated and significant adverse consequences. Addiction to painkillers such as opioids is uncommon when they are used correctly under close supervision of a physician  to control pain such a migraine attack.