Serotonin is an inhibitory neurotransmitter that is involved
in sustaining stable mood and regulating sleep cycles. Effects of neurotransmission on something such as mood or fatigue are believable because these are rooted in biological processes, but prosocial behaviour seems to be a person's own choice or free will.
Serotonin has been shown to be involved in the symptoms of major depressive disorder. The serotonin hypothesis states that low levels of serotonin in the brain play a causal role in developing depression. Studies have mainly involved clinical trials with two groups of patients, one given a drug that affects levels of serotonin in the brain and the other a placebo
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Kirsch (2014) strongly opposed both the chemical imbalance theory and, more specifically, the serotonin theory for treating depression. His analysis of both the published data and the unpublished data showed that the observed effectiveness of antidepressants can mostly be attributed to the placebo effect.
The first meta-analysis by Kirsch and Sapirstein (1998), in which they demonstrated that 75% of the improvement in the medication condition also occurred in the placebo condition, caused havoc in academic circles. Critics claimed that their selection of publications had not been representative. As a reaction to this Kirsch et al (2002) replicated the meta-analysis with a different set of clinical trials.
The Doctor Who Gave Up Drugs, a series broadcast on BBC One in 2016, which followed Sarah, a 24-year-old who had been taking antidepressants since the age of 17. She was desperate to stop her antidepressants, saying they put her in a "chemical fog". Here her love of openwater swimming is used as a possible alternative treatment for depression. This is a new feature from the BBC in the UK.
Serotonin is perhaps best known as a neurotransmitter that modulates neural activity and a wide range of neuropsychological processes, and drugs that target serotonin receptors are used widely in psychiatry and neurology. However, most serotonin is found outside the central nervous system, and virtually all of the 15 serotonin receptors are expressed outside as well as within the brain, whilst serotonin regulates a surprising number of biological processes.
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