What is serotonin syndrome?

What is serotonin? 

Serotonin is a neurotransmitter, i.e. a substance that transmits information throughout the body. It is synthesised from an amino acid: tryptophan and has many roles.

Serotonin is produced by neurons to communicate with other neurons in the brain. It is often called the "happiness hormone" because of its important effect on mood. Indeed, serotonin plays a role in the regulation of behaviour and mood, anxiety and learning. It is also involved in motivation and decision making. 

It is not only produced in the central nervous system (5% of total serotonin), but also in the blood and the intestine (95% between the two of them). In the blood it acts, in particular, on blood coagulation and on the regulation of the blood vessels diameter. In the digestive tract, it is involved in the functioning of the microbiota (the bacteria that line the inside of the intestine) and in the contraction of the intestine, thus promoting digestion.

Serotonin deficiency can lead to many symptoms and diseases, including depression. Psychological manifestations such as neurosis, anxiety, aggressive behaviour, mood disorders, panic attacks, nervousness, exhaustion and phobias can also occur.

In addition to psychological consequences listed above, serotonin deficiency can also cause physiological problems such as:

• Headaches,
• Muscle pain,
  
• Concentration problems,
  
• Sleep disorders, 
  
• Muscle pain,
  
• Sexual problems (such as premature ejaculation),
  
• Decreased libido, 
  
• High blood pressure, etc.
  

There are many causes of serotonin deficiency. For example, it can be due to :

• Lack of sunlight (sunlight stimulates the production of serotonin in the brain),
• Stress, which tends to reduce the amount of serotonin produced by the brain,
  
• Unbalanced diet. A lack of tryptophan (found in legumes, soy, brown rice, cod and fish in general, peanuts, pumpkin seeds, milk, cheese, poultry, eggs, brewer's yeast, parsley, chocolate, etc.) may lead to lack of serotonin.
  

What can you do in case of serotonin deficiency leading to depression?  

As we have seen, serotonin deficiency can be the cause of depression. Various treatments for depression exist, but the most commonly prescribed drugs are the selective serotonin reuptake inhibitors, or SSRIs. These medications increase the amount of serotonin available in the brain. SSRIs thus improve the mood and reduce anxiety.

To understand how SSRIs work, we need to look at our synapses. The synapse is where two neurons meet. The role of serotonin is to improve synaptic transmission (the passage of information from one neuron to another). 

The goal of SSRIs is to block the reuptake (reabsorption) of serotonin by the neurons. Thus, serotonin remains in the synapse for a longer period of time, increasing the stimulation of the neurons.

Nevertheless, since the 1960s, several scientific publications have reported behavioural, neuromuscular and neurovegetative manifestations following the association of substances that amplify serotonergic transmission. These publications have led to the identification of the serotonin syndrome.

What is serotonin syndrome?

Serotonin syndrome is caused by the increased stimulation of serotonin receptors in the brain. It is mainly due to the use of certain drugs (such as SSRIs, monoamine oxidase inhibitors or other antidepressants), an overdose of certain drugs or, more frequently, to undesirable drug-drug interactions. These interactions involve either two drugs that stimulate serotonin receptors when taken together or a serotonergic drug and a drug that slows down the body's elimination of the first drug (thus increasing its concentration).

Symptoms often appear within 24 hours of taking a drug or drugs affecting serotonin receptors.

The nature and severity of these symptoms can vary greatly from person to person.

Symptoms of serotonin syndrome may include:

• Anxiety,
• Agitation,
  
• Impatience,
  
• Confusion,
  
• Tremors,
  
• Muscle spasms,
  
• Muscle rigidity,
  
• Elevated heart rate,
  
• Sweating and/or chills,
  
• Vomiting,
  
• Diarrhoea.

These symptoms usually disappear within 24-72 hours of taking the drug(s), but may last longer depending on the time it takes for the body to completely eliminate the medication.

Clinical severity may range from a mild form that is difficult to identify to a rare but potentially lethal form that can provoke metabolic acidosis, rhabdomyolysis, acute renal failure, seizures, disseminated intravascular coagulation (DIC) and acute respiratory distress syndrome (ARDS).

If serotonin syndrome is diagnosed and treated promptly, the prognosis is generally good. Discontinuation of all drugs affecting serotonin receptors is necessary. Symptoms are often relieved with a sedative (e.g. a benzodiazepine), however most patients need to be admitted to hospital for further testing, treatment and monitoring.

In more severe cases, admission to an intensive care unit is necessary. Sometimes the person's body temperature needs to be cooled down using, for example, a body mist or a ventilator, and it is often necessary to measure the body temperature continuously. Patients with organ failure are also taken care of. 

In rare cases, if the symptoms do not disappear quickly, a serotonin inhibitor, such as cyproheptadine, may be administered.

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