Is Depression a Disease? -- Part II
Debunking the disease model of depression
Posted Oct 17, 2009
The disease (or defect) model of depression represents a mainstream view of this condition. In my last post, I started the series by asking whether this approach should go unchallenged. In this post, I briefly debunk four commonly held arguments that are used to support the disease model.
(1) Depression must be a disease because it is disabling and aversive. Yes, depression is horrible and undesirable and associated with impairments. Many real diseases are undesirable and associated with impairments. However, just become something is bad does not make it a disease. As Randolph Nesse has so nicely argued, fever and cough and pain are unpleasant and undesirable but far from being diseases, these responses are actually protective of health (without a capacity for pain, you are prone to become severely injured or dead!). Number one is a phony argument.
(2) But haven't scientists discovered the brain areas or regions that are responsible for depression? This one is easy. No. Although there is research that correlates patterns of brain structure or function to the symptoms of depression, almost no evidence establishes that any brain pattern is a cause of depression, as opposed to just being an effect of depression (i.e., feeling sad all the time changes brain function. Is that interesting or surprising?). In fact there are no laboratory tests of any kind, including brain images, that are truly diagnostic of depression! One common metaphor that is used to support the disease model of depression is that it is like diabetes. Leaving aside the question of whether a depressed person needs their prozac as the diabetic needs their insulin, one problem with the metaphor is that unlike diabetes (and most physical diseases), there are no diagnostic tests or even reliable signs of the disorder that are independent of the person's own report of symptoms.
(3) But isn' t it accepted that depression is genetic? If so, isn't it just a matter of time before they discover the disease genes? Yes, there is evidence that depression has substantial heritability. But this does not mean that depression is a disease. Intelligence, extraversion, and just about every trait that has been ever studied has been found to be substantially heritable but I hope you would agree that the heritability of intelligence and extraversion does not make these traits diseases! In other words, just because something is heritable (i.e., is related to genetic variation) this does not make it a disease. As far as the search for specific 'disease genes' for depression, this venture is not going well at all. Perhaps the most celebrated depression candidate gene involved the 'serotonin transporter gene.' However, the scientific evidence favoring a relationship between the serotonin transporter gene and depression has almost completely unraveled. Most behavioral genetics experts do not expect a single gene of large effect will ever be discovered to explain depression vulnerability.
(4) What about the efficacy of antidepressant medicines? Doesn't that clinch the idea that depression must be a disease? Yes, antidepressants are effective at reducing the symptoms of depression for a majority of depression sufferers. This is a good thing. However, this is not a strong clincher argument. First off, the efficacy of antidepressants is somewhat overstated. Second, these medications do not appear to have any specific efficacy for depression per ce. They are used for the treatment of a wide variety of different clinical problems including, OCD, eating disorders, and pain. If these drugs address a depressive disease, they are also addressing an OCD disease, an eating disorders disease, and a pain disease. Unless these different conditions are all the same disease it is more likely, these drugs are not treating any specific disease process per ce; rather they are having a beneficial nonspecific effect, such as improving a person's overall hedonic tone. Third, it is unwise to assume that a remedy ever tells us about original causation. Do you agree that it would be absurd to argue that because aspirin is useful for treating a headache, a headache is caused by a lack of aspirin? How different is the argument that because prozac is useful for treating a depression, a depression is caused by a lack of .......
More to come.