Addiction is usually characterized by both tolerances to the substance and withdrawal. Tolerance is a reduced sensitivity to the substance with regular consumption. Thus, the person has to consume larger amounts of the substance to achieve the same experience. It is believed that tolerance occurs because the consumption of addictive substances affects the homeostatic mechanisms. This causes the body to produce the opposite effects to those caused by the drug in an attempt to re-create a balance. Thus, larger and larger doses are required to counter these changes and achieve a ‘high’. Withdrawal is the experience of symptoms that are the opposite of what the person experiences on consuming the substance in the event that they stop consuming it.&nbsp.Withdrawal is basically a state in which the changes in the brain functioning become evident once the effect of the drug has worn off.