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Serotonin and depression24
It is unknown precisely what causes depression. It is thought to be likely that an imbalance of neurotransmitters or hormones in the body can lead to the disorder.
An association has been made between depression and serotonin, although scientists are unsure whether decreased levels of serotonin contribute to depression or depression causes a decrease in serotonin levels.
Although it is possible to measure the level of serotonin in the bloodstream, via a serum serotonin level test, it is currently not possible to measure serotonin levels within the brain. Researchers do not know whether serotonin levels in the bloodstream reflect the serotonin levels in the brain.
Serotonin levels are heavily associated with depression, although some studies have contradicted this.
It is believed that medication such as selective serotonin reuptake inhibitors (SSRIs) that can affect the levels of serotonin in the body work as antidepressants and are able to relieve the symptoms of depression. It is unknown precisely how they work, however.
A study published in 2014 may offer evidence contrary to these widely-held theories. Scientists ran mice without the capacity to create serotonin through a series of behavioral tests.The mice did not show any signs of depression, suggesting that factors other than serotonin could be involved with the development of depression.12 A similar conclusion was drawn by a professor of psychiatry writing an editorial piece for The BMJ in April 2015. He suggested that low serotonin is a mythical cause of depression.
Recent developments on the link between serotonin and depression from MNT news
A study from researchers at Duke University in Durham, NC (published in February 2015) found that mice deficient in serotonin were more vulnerable to social stressors than a group of healthy control mice.
A study in mice suggested that serotonin deficiency may not play as influential a role in depression as has previously been thought.
SSRIs and serotonin levels4
SSRIs are approved by the Food and Drug Administration (FDA) to treat depression and are the most commonly prescribed antidepressants. Common examples of SSRIs are fluoxetine (Prozac), citalopram (Celexa) and sertraline (Zoloft). The less commonly used MAOI (monoamine oxidase inhibitors) such isocarboxazid (Marplan) prevent serotonin breakdown.
Probably the most famous medical use of serotonin alteration is in the role of anti-depressants with selective serotonin (SSRIs) and norepinephrine (SNRIs) reuptake inhibitors.
Normally once a neurotransmitter has transmitted its neural impulse it is generally reabsorbed. SSRIs inhibit the re-absorption of serotonin (and norepinephrine) neurotransmitters and thus increase the levels in the synapse of the nerves in the brain, and thus elevate mood.
They are also effective in the treatment of anxiety, panic disorders and obsessive-compulsive disorders.
Recreational drugs such as MDMA and cocaine also inhibit the re-absorption of serotonin in order to create their highs.
Minor side effects of SSRIs and SNRIs that typically decrease after the first or second week of use include:4
- Weight loss or gain
- Increased sweating
- Sleepiness or insomnia
- Dry mouth
- Suicidal thoughts
- Sexual dysfunction.
SSRIs and suicide
Zoloft causes some younger users of the drug to report being suicidal. The FDA requires all antidepressants to carry a black-box warning about the danger of suicide during the initial stages of treatment, especially in children.
Antiemetics - preventing and treating nausea
The antiserotonergic drugs that act on the 5-HT3 receptors e.g. ondansetron (Zofran) are extremely important drugs used in nausea from chemical toxins such as chemotherapy drugs and drugs used in general anesthesia.
They act centrally on the area in the brain involved with nausea.
Migraine - the treatment of migraine headaches
Migraine is the most frequent neurological disorder in the adult population worldwide, affecting up to 12% of the general population.
Serotonergic vasoconstrictive antimigraine drugs - the Triptans - e.g. almotriptan (Axert), Rizatriptan (Maxalt), sumatriptan (Alsuma) and zolmitriptan (Zomig) are effective in reducing migraine symptoms and are well tolerated.5
Appetite suppressants - to help reduce obesity
Serotonergic appetite suppressants such as fenfluramine (Pondimin) and chlorphentermine - are no longer licensed for this use.
Several functions have been attributed to the serotonergic system including cognition, emotion and motor behavior; thus altered serotonergic neurotransmission may contribute to the motor and non-motor features commonly associated with Parkinson's disease.6
Serotonergic anti-Parkinsonian drugs (pergolide, cabergoline) have been used in the treatment of Parkinson's disease and are no longer licensed, but research continues in this area.
The cause of premenstrual syndrome (PMS) is unknown, but an over sensitivity to one of the female hormones, progesterone, seems to reduce the level of serotonin in the brain.
Some SSRIs are licensed to help women through difficult physical and emotional symptoms around the changes in their monthly menstrual cycle, even if the woman is not clinically depressed. The drug need not be taken throughout the whole cycle, and women may find relief within a few days of starting to take it.7
New research is examining the role of serotonin inhibition in treating obesity.8
Irritable bowel syndrome
Work continues to evaluate the evidence of the value and safety of serotonin receptor modulation in irritable bowel syndrome. Alosetron and cilansetron are currently in use in the US.
The FDA have issued a warning about taking SSRIs or SNRIs (used for depression, anxiety, pain, and many other conditions) with triptans. Taking these medicines together can cause a very rare but serious condition called serotonin syndrome.
On the final page we look at 'serotonin syndrome' and we discuss some natural ways to boost serotonin levels.