A chemical imbalance in depression affects 10% at most.
Personal stories on depression and statistics from mental health organisations are in our newspapers on almost a daily basis, so it’s obviously a very topical issue at the moment. According to the OECD, Ireland’s suicide rate is 11 per 100,000 population which is just below the EU average of 12.2 percent, however there will always be incidents of suicide that are not reported as such. Many voluntary organisations are working hard to support people who are suffering from mental health illnesses, although as with almost everything these days, someone somewhere is profiting from it.
Pharmaceutical companies sell antidepressants on the basis that they correct a chemical imbalance in the brain of the sufferer. The research suggests that there may be a chemical imbalance (i.e. a deficiency in the neurotransmitter serotonin) in some people with depression, however it is not the only possible cause of the condition. "Less than 10% of clinical depression is thought to have a chemical basis. Appropriate psychotherapy has still been shown to be more effective than drug treatment alone in the treatment of chemically based depression, and far more effective in preventing relapse. By far the majority of depressions are learned phenomena, not chemical ones.” 
The concern is that many people believe that the chemical imbalance (if it is present in the patient) causes the condition. Psychologist Christopher M. France of Cleveland State University and his colleagues discovered that 84.7 percent of participants found it “likely” that chemical imbalances cause depression. The only thing that this shows us is that the pharmaceutical companies have done an excellent job of advertising the chemical imbalance deficiency, as a likely cause of depression.
Supposing there was evidence of a chemical imbalance in 100% people suffering with depression, considering everyone has a different life story and unique circumstances, it would still be extremely difficult to ascertain whether or not there was correlation or causation between the imbalance and depression. For example, "Aspirin alleviates headaches, but headaches are not caused by a deficiency of aspirin.” Hal Arkowitz, Associate Professor of Psychology, University of Arizona.
The idea that anitdepressnats have been willingly accepted by the entire medical community is not true and neither is the notion that they unequivocally agree with the industry-backed studies that have been published. Also, many books have been written on the subject such as Pharmageddon and Bad Pharma. Dr. Ben Goldacre has two TED Talks on how the results of the double-blind placebo controlled studies are not always accurate. “In fact, seven trials were conducted comparing reboxetine against a dummy placebo sugar pill. One of them was positive and that was published, but six of them were negative and they were left unpublished. Three trials were published comparing reboxetine against other antidepressants in which reboxetine was just as good, and they were published, but three times as many patients' worth of data was collected which showed that reboxetine was worse than those other treatments, and those trials were not published. I felt misled.” - Dr. Ben Goldacre, British Physician.
Even if we include the carefully selected clinical trials that are presented by the drug companies, the efficacy of the drugs for people with low mood is still poor. "When FDA clinical trial data are aggregated, antidepressants do outperform placebo pills for people who have severe depression, but there is minimal benefit for mild or moderate depression.” 
Furthermore, for patients with more serious issues relating to depression, antidepressants are not always very effective and often don’t perform nearly as well as sugar pills.
Still, 10% of people responding to the antidepressants should be enough to warrant the continuation of research in this area and the use of the drugs themselves, however anyone considering taking them should determine whether or not the negative side-effects that they may experience such as nausea, weight gain and sexual problems, are worth the risk. 
One of the biggest problems is that some people who are told they have an imbalance tend to lose hope in any sort of talk therapy or cure that isn’t a pill. "Recent experiments show that presenting depressed people with the idea that they have a chemical imbalance makes them more pessimistic about the future, does not reduce self-blame, and undercuts their view about whether psychological therapy will help.”
Finally, there are some interesting facts, stats and expert viewpoints. Of course you can take or leave any and all of those points, but I wonder what answer you’ll get if you ask yourself the following question. Considering that everyone has a unique set of experiences, circumstances and subjective interpretations of life events, how well could a variation of an antidepressant adjust to all of those complexities so as to best serve each individual suffering from a condition that cannot be seen?
- Tyrrell, M. and Elliott, R. Is depression caused by chemical imbalance? Retrieved from: http://www.clinical-depression.co.uk/depression-faq/is-depression-caused-by-chemical-imbalance/ [Accessed (March 27, 2015]
- Healy, D. Pharmageddon, University of California Press; 1 edition (March 12, 2012)
- Goldacre, B. (June 2012). What doctos don’t know about the drugs they prescribe, Retrieved from: http://www.ted.com/talks/ben_goldacre_what_doctors_don_t_know_about_the_drugs_they_prescribe?language=en
- Coping With Side Effects of Depression Treatment. Retrieved from: http://www.webmd.com/depression/features/coping-with-side-effects-of-depression-treatment [Accessed March 27, 2015]
- Rothenburg, J. Ten troubling facts about anti-depressants, Retrieved from:https://www.psychologytoday.com/blog/charting-the-depths/201404/10-troubling-facts-about-antidepressants [Accessed March 27, 2015]
- Jay C. Fournier, MA; Robert J. DeRubeis, PhD; Steven D. Hollon, PhD; Sona Dimidjian, PhD; Jay D. Amsterdam, MD; Richard C. Shelton, MD; Jan Fawcett, MD, Antidepressant Drug Effects and Depression Severity. Retrieved from: http://jama.jamanetwork.com/article.aspx?articleid=185157 [Accessed March 27, 2015]
- Joshua J. Kempa, James J. Lickel b, Brett J. Deacon (February 2014) Effects of a chemical imbalance causal explanation on individuals’ perceptions of their depressive symptoms, Retrieved from: http://www.uw-anxietylab.com/uploads/7/6/0/4/7604142/chemical_imbalance_test_brat.pdf [Accessed (March 27, 2015]
- Arkowitz, H. and Lilienfeld, S.O. Is depression just bad chemistry? Retrieved from: http://www.scientificamerican.com/article/is-depression-just-bad-chemistry/ [Accessed March 27, 2015]
- Suicide rates hit an all-time high as 554 take own lives. Retrieved from:
- http://www.independent.ie/irish-news/health/suicide-rates-hit-an-alltime-high-as-554-take-own-lives-30601624.html [Accessed March 27, 2015]
- Ireland’s suicide rate is below EU average – OECD report. Retrieved from: http://www.thejournal.ie/ireland-oecd-study-1369502-Mar2014/ [Accessed March 27, 2015]