How do SSRIs work?

SSRIs exert their effect by inhibiting a serotonin transporter at the presynapse. Under normal circumstances, the serotonin from the synaptic cleft would be returned to the presynapses by this transporter, where it would be “packed” into small transport vesicles and released into the synaptic cleft again during a new synaptic transmission process. If the activity of the serotonin transporter is reduced, the serotonin cannot enter the synapse again and remains in the synaptic cleft.

However, since new serotonin is constantly being produced in the presynapse and prepared for release, the next time the transport vesicles are emptied, a veritable “serotonin avalanche” occurs in the gap between the synapses. The accumulation of serotonin is then usually sufficient to ensure synaptic transmission. At the post-synapse, sufficient amounts of serotonin activate the target structures of the substance, so-called receptors.

These receptors are located in the outer wall (membrane) of the postsynapse, penetrate it and are connected to small proteins inside the postsynapse. If serotonin docks to its receptor, its shape changes. This process also “moves” the small proteins inside, the signal is further amplified and continues in a “waterfall” fashion. It can reach the respective target region in the body and develop the desired effect there. However, serotonin transporters are not only present at the presynapses but also in some other parts of the body, such as the blood platelets (thrombocytes), which can lead to undesired effects when SSRIs are used.

Side effects of SSRI

In addition to the desired therapeutic effects, SSRIs have a number of unpleasant side effects. Common symptoms include dry mouth, abnormal sweating, headaches, tremors, and fatigue with simultaneous restlessness and insomnia. A particularly annoying, undesirable effect of SSRIs is the nausea that often occurs.Serotonin binds mainly in the digestive tract and in the nausea center of the CNS to target structures which have a stimulating effect on the nausea stimulus (emetic).

This causes annoying nausea, which is sometimes accompanied by vomiting, loss of appetite and weight loss. SSRIs can also have negative effects on potency and libido (desire for sexual intercourse). Another effect that should not be underestimated is the tendency to bleed when taking SSRI.

Under physiological (“normal”, healthy) conditions, serotonin mediates an important effect on the blood platelets (thrombocytes) by ensuring that they are stored together. In the event of injury, many platelets “stick” together to form a clot, which ensures wound closure and hemostasis immediately after tissue damage. If a patient takes SSRI, the serotonin transporter that transports the substance into the platelets is also inhibited.

If no serotonin reaches the blood platelets, they can no longer completely congregate and the time to hemostasis increases. Patients under SSRI influence should therefore always check whether they bleed for an unusually long time. In women, prolonged or increased menstruation can indicate prolonged bleeding times.

Particularly serious side effects of SSRI are associated with the so-called serotonin syndrome. Overdosage with SSRI and the resulting excessive amount of serotonin in the body causes severe abdominal pain with fever, high blood pressure, palpitations and general restlessness. If untreated, serotonin syndrome can be fatal if the stress on the circulation exceeds tolerable levels and the body’s own regulatory mechanisms fail.

Weight gain plays a minor role in SSRIs compared to tricyclic antidepressants. On the contrary, weight loss usually occurs due to a reduced feeling of hunger and reduced food intake. Weight gain when taking SSRIs is therefore not a direct side effect of the drug.

To prevent weight gain, the patient must monitor his or her food intake. An increased intake of calories over consumption leads to the build-up of fat reserves and makes the body weight increase. Patients should generally follow a balanced diet and use natural foods rather than highly processed junk food.

The choice of food also plays a role: protein-rich and fibre-rich products saturate carbohydrates over the long term, just as complex as in wholemeal products. In the case of fats, unsaturated fatty acids should be used in particular, as in fish and nuts. Physical activity also plays a major role in preventing weight gain.

Increased activity increases consumption and metabolic performance and can support active weight control. Our next article could also be interesting for you:

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Sexual dysfunction is considered a possible side effect of SSRI therapy. Symptoms include impotence, premature ejaculation, anorgasmia (disturbance of orgasm) and reduced or absent libido.

The frequency and severity of these side effects depends largely on the choice of the preparation. Sexual dysfunction can, but does not have to occur in every treated person. If the symptoms mentioned above occur, a change to another SSRI may be advisable. Our next article may also be of interest to you: Cause of erectile dysfunction