(Harvard): People sometimes confuse the words tolerance, physical dependence and withdrawal. Although related, these terms are not interchangeable.

• Tolerance means that, over time, a person will need larger doses to get the same effect first experienced with smaller doses. Because tolerance to some side effects does not occur, people with tolerance often face worsening side effects as they take larger and larger doses.
• Physical dependence means that the body gets used to having the substance or activity and "misses it" if its taken away. People with physical dependence who stop using their object of dependence or who decrease their dose might develop uncomfortable withdrawal symptoms.
• Withdrawal refers to a range of typical symptoms that vary depending on the substance or activity in question, but they often reflect the opposite of the high. How long withdrawal symptoms last and how severe they are depends on which substance (or activity) a person uses, at what dose, and for how long. The fear of withdrawal symptoms sometimes makes people nervous about stopping or lowering their dose. Thats sometimes true even for people who no longer derive pleasure from their object of addiction.