We explain for what case each type of antidepressant is designed.
Antidepressants are drugs used to treat depressive disorders . However, they also have many other indications, and are used to treat different anxiety disorders and other types of disorders.
In this article we will learn about the four types of antidepressants that exist (and some of their subtypes): we will analyze their characteristics, examples, mechanism of action, indications, side effects and adverse reactions.
- Recommended article: “The 4 types of anxiolytics (uses, effects and indications)”
Antidepressants: characteristics
Its mechanism of action changes from one antidepressant to another; that is why there are different types of antidepressants, classified into different groups, mainly according to their mechanism of action.
Generally, however, antidepressants achieve their effects (reducing depressive symptoms and improving mood) by increasing certain substances in the brain: dopamine (DA), serotonin (SA) and norepinephrine (NA).
That is, antidepressants are generally agonists of these three monoamines (SA, NA and DA); in turn, these substances are divided into two chemical groups. Thus, while dopamine and norepinephrine are catecholamines, serotonin is an indolamine.
These three substances mentioned are, in turn, three types of neurotransmitters, and have a key role in mood and depressive symptoms. As we will see, to achieve this increase, they are based on selectively inhibiting the receptors of these substances (this is the case of SSRI, ISRN, dual antidepressants…), or on blocking the action of an enzyme that degrades them (types of MAOI antidepressants). , etc.
Types of antidepressants
We are going to see what the different types of antidepressants consist of , according to their mechanism of action.
In addition, we will review them in chronological order of discovery (with those that were discovered first first):
1. MAOIs
The first of the types of antidepressants are MAOIs (Monoamine Oxidase Inhibitors) . They were the first antidepressants discovered and used, and therefore, they are the oldest. What they do, as their name suggests, is to inhibit monoamine oxidase (MAO). Monoamine oxidase is an enzyme that breaks down amines in the brain (serotonin, dopamine, and norepinephrine).
By degrading them, their brain concentration decreases; That is why MAOI antidepressants, by blocking this action, increase the concentration of amines. In depression, these substances are found in low concentrations; by increasing them, depressive symptoms improve. This is how MAOIs work.
1.1. Types of MAOs
There are two types of monoamine oxidases (MAOs): MAO A and MAO B. MAO A metabolizes norepinephrine, serotonin (5-HT), and tyramine (which increases norepinephrine), while MAO B metabolizes only dopamine and tyramine.
1.2. Types of MAOIs
Consequently, there are two types of MAOI antidepressants: type A and type B. Type A MAOIs are used to treat depression (since norepinephrine and serotonin are associated with depression), and MAO Bs are used to treat depression. Parkinson’s (since dopamine is altered in this disease).
1.3. MAOI and RHYMES
In turn, this type of antidepressant can be MAOI (irreversible and non-selective, which inhibit both MAO A and MAO B) or RIMAS [IRMAS] (reversible and selective, which only inhibit MAO A, without destroying it) .
MAOIs, unlike RIMAS, do destroy MAO (and it takes up to 15 days to synthesize new enzyme). MAOIs increase serotonin, norepinephrine, dopamine, and tyramine levels.
One of its side effects is that it increases blood pressure; Associated with them is the so-called “risk of the cheese effect”, which consists of the risk of suffering a hypertensive crisis, a cardiovascular condition and hemorrhage, due to eating foods that contain tyramine (such as cheese).
This happens because when taking MAOIs, tyramine increases in concentration, and if more tyramine is also consumed, the concentration is excessive, producing this hypertensive risk. The RIMAS, for its part, increase the levels of norepinephrine, serotonin and tyramine. They have fewer side effects than MAOIs, and less associated risk of the so-called “cheese effect.” An example of a RIMA is moclobemide.
1.4. Indications
The indications for these types of antidepressants (IMAO and RIMAS) are: atypical depression, panic disorder and social phobia .
2. Tricyclic antidepressants
The second types of antidepressants to be discovered and marketed are tricyclic antidepressants . Their name is due to their chemical structure, which is tricyclic (they are formed by chains of three rings). Some of them are: clomipramine, imipramine, amitriptyline, doxepin, desipramine…
As for their therapeutic effects, what this type of antidepressant does is inhibit the reuptake of norepinephrine (NA), serotonin (5-HT) and dopamine (DA). That is, they are agonist drugs. Its therapeutic effects (reduction of depressive and/or anxious symptoms) appear 2 or 3 weeks after starting treatment. Its side effects, on the other hand, appear earlier (from the first shot).
Other chemical effects of these types of antidepressants are the antagonism of acetylcholine (Ach) (they decrease its concentration), and the antagonism of histamine. They also block a receptor called alpha-adrenergic receptors.
2.1. Side effects
All these effects related to different substances and receptors, entail important secondary effects. The antagonism of acetylcholine produces the so-called “anticholinergic effect”, which consists of the appearance of sedation, dry mouth, urinary retention, constipation and cognitive blunting.
Histamine antagonism produces the “antihistamine effect,” which leads to sedation and weight gain. Finally, blockade of alpha-adrenergic receptors causes orthostatic hypotension, dizziness, and drowsiness.
2.2. Adverse reactions
The adverse reactions (which are usually more serious and less frequent than the side effects) of this type of antidepressants, the tricyclics, include the appearance of hypomania (in people over 50 years of age) and the so-called “Neuroleptic Malignant Syndrome” (NMS) .
NMS includes the following symptoms: high fever, muscle rigidity, arrhythmias, dyspnea, and cyanosis. One in five patients with NMS dies, and it is a fairly common syndrome.
23. Indications
Tricyclics are indicated for all cases of depression, especially for melancholic depression.
They are also indicated for some anxiety disorders (panic disorder and generalized anxiety disorder [GAD]: in these cases, the ideal is imipramine and clomipramine), OCD (obsessive-compulsive disorder) (imipramine), anorexia (imipramine ), chronic pain (amitriptyline, which is also used in post-traumatic stress disorder [PTSD]), and childhood bedwetting (imipramine).
3. SSRIs
SSRIs (Selective Serotonin Reuptake Inhibitors), as their name suggests, inhibit serotonin reuptake, increasing the concentration of this substance in the brain . Therefore, they are serotonin agonists. Some of them are fluoxetine, paroxetine, sertraline, citalopram and escitalopram.
SSRIs are one of the most widely used types of antidepressants today, as they produce fewer side effects than the previous types. Its therapeutic effects appear after 2 weeks of starting its intake, and side effects, before 2 weeks.
3.1. Indications
SSRIs are used for depression and depressive symptoms of adaptive conditions; also in OCD, in anxiety disorders (panic disorder, GAD, social phobia and PTSD [paroxetine]), as well as in bipolar disorder. Fluoxetine is often used in bulimia. Finally, they are also indicated for impulse control and chronic pain.
3.2. Side effects
Side effects of SSRIs include: sexual dysfunction, increased anxiety on first shots, gastrointestinal discomfort, and sleep and movement disturbances.
4. Fourth generation antidepressants
The latest and most recent types of antidepressants are the 4th generation antidepressants . The two best known are reboxetine and venlafaxine.
Reboxetine selectively inhibits norepinephrine reuptake, and is a perfect complement to some SSRIs. For its part, venlafaxine dually inhibits the reuptake of serotonin and norepinephrine (it is an agonist). Venlafaxine is the disorder of choice for GAD. Another dual antidepressant is duloxeine.
These types of antidepressants, the dual ones, are the ones with the fewest side effects, since they do not affect histamine or acetylcholine.
Bibliographic references
- Ban, T.A. (2001). «Pharmacotherapy of mental illness-a historical analysis.». Progress in neuropsychopharmacology & biological psychiatry.
- Stahl, SM (2002). Essential psychopharmacology. Neuroscientific bases and clinical applications. Barcelona: Ariel.
To the classic question “what do you do?” I always answer “basically I am a psychologist”. In fact, my academic training has revolved around the psychology of development, education and community, a field of study influenced my volunteer activities, as well as my first work experiences in personal services.