There can be a great deal of confusion surrounding the words addiction, physical dependence, and tolerance. People will use these words as if they are referring to the exact thing, but there is a significant difference between them. Misunderstandings about these terms can not only be confusing for the general public but also many in the medical profession. One of the main culprits blamed for this confusion is the fact that the Diagnostic and Statistical Manual of Mental Disorders has chosen to use the word dependency instead of the word addiction and people assume this to mean physical dependency.
Tolerance refers to a physiological state where the effectiveness of a drug has decreased due to chronic administration. This means that more of the drug will be required to achieve the same effect in the future. One of the reasons for why this occurs is that any organism can build up a resistance against the effects of some drugs.
There are said to be two mechanisms involved in tolerance: pharmacokinetic tolerance and pharmacodynamic tolerance. With pharmacokinetic tolerance there is a decreased quantity of the substance reaching the target area. There are different reasons for why this can occur but a common example is that there has been an increase in enzymes that lead to degradation of the drug. Pharmacodynamic tolerance occurs because there is a decreased response to the drug by the cellular mechanism. A common way that this happens is that there has been a reduction in the number of receptors.
Physical dependence refers to how the body experiences physiological adaptation in response to chronic use of a drug. Humans adapt so well to having these substances in their system that they suffer negative consequences if the drug is stopped abruptly – these are referred to as withdrawal symptoms. These withdrawal symptoms do not only occur with recreational drugs – they can also occur with other medications such as antidepressants. Those who develop a physical dependence will often usually develop tolerance to the drug as well. It differs from addiction because it is a physiological state and not a dysfunctional behavioral syndrome. It would be correct to say that most addicts will have developed a physical dependence on their drug.
Addiction can be defined as the compulsive use of drugs for non-medical reasons. The individual is likely to have developed physical as well as psychological dependence on the symptoms. This means that as well as feeling physically unwell when they stop the substance they will also feel psychologically unable to cope without the substance. In most instances the individual will have developed a tolerance to the euphoric effects of the drug so they will need to keep on taking more and more of it. Tolerance and physical dependence are physiological changes while addiction is a type of behavior.