Of all the psychotropic drugs, the serotonin reuptake inhibitors (SSRIs) are the most prescribed both in Spain and in most industrialized countries. This type of antidepressant is popular for several reasons: it is indicated for the most prevalent disorders such as major depression or anxiety disorders, they are effective and their side effects are almost always well tolerated.

If we understand why depression occurs, we can also understand how SSRIs are effective in treatment and through what mechanism they act . We will briefly review how they work, what their properties and adverse effects are and in which disorders they are most frequently prescribed.

What is an SSRI?

Although it can be cumbersome, it is necessary to understand how neurons function at the cellular level when they communicate with each other through neurotransmitters in order to understand how serotonin reuptake inhibitors modify neuronal activity.

Serotonin release and reuptake

When the neurons communicate with each other, the presynaptic neuron (the emitter of chemicals that the other will receive) releases neurotransmitters into the synaptic space, which are picked up by the receptors of the postsynaptic neuron . In the case of the neurotransmitter circuits called serotonin, neurons use this neurotransmitter to communicate. One neuron releases serotonin into space and the other collects it, understanding that it must be activated.

What happens is that not all the neurotransmitters are received and sometimes they remain floating in the intersynaptic space. There are some pumps that are responsible for cleaning this neurotransmitter that is left over and return it to the presynaptic neuron.

In depression and other disorders, it is hypothesized that there is very little serotonin in this space, so that post-synaptic, serotonin-hungry neurons create many receptors to receive neurotransmitters but are not activated and do not release anything, as in a state of hibernation.

SSRIs block reuptake pumps and allow more and more serotonin to build up in space. Post-synaptic neurons, because they sense that the concentration of serotonin in space is higher and more neurotransmitter is available, begin to decrease the number of receptors because they no longer think they need so many. The neuron relaxes its strict rule of not releasing anything, and begins to let go of serotonin and activate the rest of the neurons in the circuit.

Types of SSRIs

Not all SSRIs are the same. Each drug uses a different active ingredient that will have a specific therapeutic dose.Also, because each active ingredient acts on different serotonin receptors , its side effects will also be different. It is this relationship between the efficacy, safety and tolerance of the drug that defines whether it is preferable to use one or the other.

Below is a list of the SSRIs on the market. In pharmacies we will find them under different trade names depending on the country. For example, fluoxetine is more widely known as Prozac , or escitalopram under the name Cipralex:

  • Citalopram
  • Escitalopram
  • Fluoxetine
  • Fluvoxamine
  • Paroxetine
  • Sertraline

Safety, Tolerance and Side Effects

In general, SSRI psychotropic drugs are safe . Unlike lithium salts, the toxic dose is difficult to achieve by mistake when taking SSRIs. Also, they do not produce the same tolerance as other drugs such as benzodiazepines, so there is no need to increase the dose because of the properties of the SSRI.

On the other hand, the side effects it produces are minor . They can produce nausea, dry mouth, sweating, anorgasmia, decreased sexual desire and blurred vision, among others, which are much less frequent. Abrupt cessation of SSRI use, although not addictive, can cause withdrawal, as the brain becomes accustomed to the presence of the substance. For this reason, the withdrawal of the drug is done gradually.

The SSRIs interact with many other medications , so close supervision by the prescribing psychiatrist is necessary. For example, some antidepressants remain in the system for days or weeks after they are stopped. When someone taking this type of antidepressant switches to SSRIs, there may be an overlap between the effects of the previous medication that has not yet been excreted and the SSRIs. This causes the patient to suffer from serotonin syndrome, an excess of serotonin causing a confusional state, agitation, headache, nausea, etc. and must be treated urgently.

Uses in Psychiatry

Like tricyclic antidepressants, SSRIs are used for a wide variety of disorders. Naturally, the main use is in patients with major depressive episodes or depressive symptoms. The use of SSRIs is very effective in ending the depressive symptomatology that may be found in patients with anxiety disorders, personality disorders, gender dysphoria, bulimia nervosa, autism, etc.

Because serotonin is also involved in anxiety, the benefit of SSRIs in anxiety disorders is often twofold. On the one hand it calms the negative mood, and on the other it reduces the experience of anxiety . Especially in patients who experience chronic levels of anxiety such as in generalised anxiety disorder, obsessive-compulsive disorder, post-traumatic stress or acute stress reactions, serotonin reuptake inhibitors will be very useful.

These patients, when taking SSRIs, experience a significant drop in anxiety levels. This allows them to release the worries and anxiety that torment them, regaining much of their quality of life and leading a functional life.