I am a depression patient. It is certainly true that various substances can induce depression. I do not believe that the original poster was implying that depression is without very real biological causes; merely that these causes are more nuanced than the phrase "chemical imbalance" implies. Here is some food for thought.
SSRIs, or serotonin reuptake inhibitors, are the most commonly prescribed antidepressants in the United States due to their relative safety and efficacy. It is widely thought that these drugs achieve effectiveness through their ability to increase serotonin levels in the brain. Now, here comes the mystery: while serotonin levels rise almost immediately following introduction of the drug, the antidepressant effects do not become apparent until several weeks of treatment have passed. Why is that? No one knows for sure, but a few interesting theories have emerged.
The most interesting theory, in my opinion, involves hippocampal neurogenesis and BDNF levels. A few recent studies have shown that one thing that the SSRIs share in common is that they all promote neurogenesis in the hippocampus. A further study showed that the antidepressant effects of SSRIs on behavior in rats exposed to artificially induced stressors could be completely nullified by slightly irradiating the hippocampus, thus negating the growth of new neurons promoted by the SSRIs. The antidepressant effect was gone even though serotonin levels remained elevated.
This conclusion provided compelling but not conclusive evidence that neurogenesis is involved in antidepressant effectiveness. Yet even here, the picture was not altogether clear: while patients diagnosed with clinical depression generally show less hippocampal neurogenesis than controls, it is not at all clear whether this deficit is a cause or effect of clinical depression. Is it possible that depression, once established, can cause physical changes in brain structure? If so, that might explain why cognitive behavioral therapy in conjunction with antidepressant medication is a more effective depression treatment than either of the two alone.
Interestingly enough, strenuous aerobic exercise is known both to be an effective treatment for mild to moderate forms of depression as well as a promoter of hippocampal neurogenesis. An increasing number of psychiatrists are in fact prescribing exercise regimens as treatment for some forms of depression because it seems to work.
The bottom line is: there's a lot we don't know about depression, and while we have effective treatments, the reality is that the causes of depression simply cannot be adequately summed up as a "chemical imbalance." Drugs are appropriate for some patients and inappropriate for others. I encourage anyone interested in the subject to do some reading, as the brain is (at least, to a layman like me) the most fascinating information processing system ever.
While we don't know the exact causes, and there are complex factors in play, it is most certainly a chemical imbalance. Imagine you could take a perfect chemical "snapshot" of the brain/body when it's in a normal mood and again in depressed state. Do you seriously think there would be no difference chemically?
I've take SSRIs off & on for the last 15 years. I'm currently on them after experiencing suicidal depression this summer. (I suspect it was partially induced by taking Chantix.)
Exercise can help, but in my case it doesn't make much difference. When my latest onset hit I was (and still am) in the best shape of my life and maintaining 10% body fat. I've been doing Crossfit for the last 15 months. Very strenuous.
"Do you seriously think there would be no difference chemically?"
No, I do not think that. In fact, I stated quite clearly that depression causes measurable changes in brain morphology and function. My entire argument was to support the assertion that the phrase "chemical imbalance" is merely an insufficient label for a complex psychological and biological phenomenon.
SSRIs, or serotonin reuptake inhibitors, are the most commonly prescribed antidepressants in the United States due to their relative safety and efficacy. It is widely thought that these drugs achieve effectiveness through their ability to increase serotonin levels in the brain. Now, here comes the mystery: while serotonin levels rise almost immediately following introduction of the drug, the antidepressant effects do not become apparent until several weeks of treatment have passed. Why is that? No one knows for sure, but a few interesting theories have emerged.
The most interesting theory, in my opinion, involves hippocampal neurogenesis and BDNF levels. A few recent studies have shown that one thing that the SSRIs share in common is that they all promote neurogenesis in the hippocampus. A further study showed that the antidepressant effects of SSRIs on behavior in rats exposed to artificially induced stressors could be completely nullified by slightly irradiating the hippocampus, thus negating the growth of new neurons promoted by the SSRIs. The antidepressant effect was gone even though serotonin levels remained elevated.
This conclusion provided compelling but not conclusive evidence that neurogenesis is involved in antidepressant effectiveness. Yet even here, the picture was not altogether clear: while patients diagnosed with clinical depression generally show less hippocampal neurogenesis than controls, it is not at all clear whether this deficit is a cause or effect of clinical depression. Is it possible that depression, once established, can cause physical changes in brain structure? If so, that might explain why cognitive behavioral therapy in conjunction with antidepressant medication is a more effective depression treatment than either of the two alone.
Interestingly enough, strenuous aerobic exercise is known both to be an effective treatment for mild to moderate forms of depression as well as a promoter of hippocampal neurogenesis. An increasing number of psychiatrists are in fact prescribing exercise regimens as treatment for some forms of depression because it seems to work.
The bottom line is: there's a lot we don't know about depression, and while we have effective treatments, the reality is that the causes of depression simply cannot be adequately summed up as a "chemical imbalance." Drugs are appropriate for some patients and inappropriate for others. I encourage anyone interested in the subject to do some reading, as the brain is (at least, to a layman like me) the most fascinating information processing system ever.