SSRI: types, functioning and effects of this antidepressant

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

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

• Related article: "Psychopharmaceuticals: drugs that act on the brain"

What is an SSRI?

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

• You may be interested: "Types of neurons: characteristics and functions"

Serotonin release and reuptake

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

What happens is that not all neurotransmitters are received and sometimes it remains floating in the intersynaptic space. There are pumps that are responsible for cleaning this excess neurotransmitter and returning it to the presynaptic neuron.

In depression and other disorders it is hypothesized that there is very little serotonin in this space, so that postsynaptic neurons, starved for serotonin, they 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 they allow more and more serotonin to accumulate in space. Postsynaptic neurons, as they perceive that the concentration of serotonin in space is higher and there is more neurotransmitter available, they begin to decrease the number of receptors because they no longer believe they need so many. The neuron relaxes its strict rule of releasing nothing, and begins to release 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, as 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 you can see a list of the SSRIs marketed. In pharmacies we will find them under different commercial names depending on the country. For example, fluoxetine is more widely known as Prozac, or the escitalopram under the name of Cipralex:

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

Safety, tolerance and side effects

In general, SSRI psychotropic drugs are safe. Contrary to what happens with lithium salts, the toxic dose is difficult to reach by mistake when we take SSRIs. Likewise, they do not produce the same tolerance as other drugs such as benzodiazepines, so that it is not necessary to increase the dose due to the properties of the SSRI.

On the other hand, the side effects it produces are minor. They can cause nausea, dry mouth, sweating, anorgasmia, decreased sexual desire and blurred vision, among others much less frequent. The abrupt cessation of SSRI use, even if it does not generate addiction, can cause withdrawal, as the brain gets used to the presence of the substance. For this reason, the withdrawal of the drug is done gradually.

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

Uses in psychiatry

In the same way as 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 it is very effective to end depressive symptoms that can be found in patients with anxiety disorders, personality disorders, gender dysphoria, bulimia nervosa, autism, etc.

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

These patients, when taking SSRIs, experience a significant decrease in anxiety levels. This allows them to loosen the worries and restlessness that torments them, recovering much of their quality of life and leading a functional life.