Tricyclic antidepressants: uses and side effects
Although today they are less used than the SSRIs and other more modern antidepressants, the tricyclics were for many decades the pharmacological treatment of choice for depressive disorders.
In this article we will describe What are tricyclic antidepressants? , what they are used for and what are their most common side effects.
- Related article: "Types of antidepressants: characteristics and effects"
What are tricyclic antidepressants?
Tricyclics are psychotropic drugs that are used to treat depressive disorders s, although in many countries they have been replaced as drugs of choice by other more effective antidepressants. The effects of drugs useful in treating depression are usually related to the agonism of serotonin and norepinephrine.
The name of these drugs comes from their chemical structure: they are composed of three rings of atoms. Years after the advent of tricyclic antidepressants, tetracyclics also appeared, which are formed by four rings instead of three.
From the moment it appeared imipramine, the first antidepressant of this class , a large number of tricyclics have been manufactured with some differential characteristics. Among the most common are clomipramine, amitriptyline, nortriptyline, desipramine, maprotiline, doxepin, amoxapine, protriptyline and trimipramine.
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What is your mecanism of action?
The tricyclic antidepressants are agonists of the monoamines, a type of neurotransmitter very relevant in the nervous system of human beings. These potentiating effects affect serotonin, norepinephrine and, less significantly, to dopamine.
Its main therapeutic activity is due to the inhibition of the reuptake of these neurotransmitters, which increases the availability of monoamines in the synaptic space. However, also affect collateral histamine and acetylcholine , on which they exert an antagonistic effect.
Due to the low specificity of its mechanism of action, which are not directed only to the most relevant neurotransmitters as with other antidepressants, tricyclics may be useful to relieve symptoms of depression but also cause side effects and very significant adverse reactions.
History of these drugs
The tricyclics were discovered in the manufacturing process of antipsychotic drugs. In 1950, clomipramine, a neuroleptic with a tricyclic structure, was synthesized . Information about this drug led soon after to the creation of imipramine, the first tricyclic used specifically to treat depression.
In recent decades the popularity of tricyclics has declined in most parts of the world due to the discovery of more effective and safe antidepressant drugs, particularly selective serotonin reuptake inhibitors (SSRIs) and fourth generation antidepressants, such as venlafaxine and reboxetine.
Its functions
Despite its name, tricyclic antidepressants are not used only in cases of depression, but throughout its history have been applied to a large number of different psychological disorders.
1. Depressive disorders
The main indication of tricyclics is the treatment of depressive disorders , both major depression and other milder variants, particularly dysthymia. Currently they are prescribed mostly in melancholic depression and in cases that do not improve by the consumption of other antidepressants with fewer side effects.
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2. Anxiety disorders
Some tricyclics are occasionally used to treat various anxiety disorders: imipramine has been shown to be effective in generalized anxiety disorder and panic disorder, while clomipramine is still used in cases of obsessive-compulsive disorder (very related to depression) and amitriptyline in post-traumatic stress.
- Related article: "Obsessive-Compulsive Disorder (OCD): what is it and how does it manifest?"
3. Chronic pain
Among the disorders related to chronic pain that have been treated by tricyclic include fibromyalgia and neuropathic pain; It is believed that the agonism of serotonin and norepinephrine indirectly influences the production of endogenous opioids , which have analgesic effects. Amitriptyline seems to be especially useful in this regard.
4. Insomnia
The sedative side effects of tricyclic antidepressants have led to their being used occasionally to treat insomnia symptoms. However, it is important to bear in mind that there are other more specific drugs for these problems, and above all that psychological therapy is the most recommendable way to face the difficulties to sleep.
5. Eating disorders
Again, the therapeutic effects of tricyclics in eating disorders they are associated with one of its most frequent side effects : the weight gain. In particular, clomipramine is sometimes prescribed as part of therapy for anorexia nervosa.
6. Night enuresis and night terrors
Imipramine is effective in treating two childhood sleep disorders: nocturnal enuresis and nocturnal terrors. These effects are related to the decreased delta sleep or slow waves , during which these episodes appear.
- Related article: "Types of brain waves: Delta, Theta, Alpha, Beta and Gamma"
Side effects of tricyclic antidepressants
Although the side effects associated with the use of tricyclic antidepressants depend in large part on their agonism or antagonism to certain neurotransmitters, in this section we will focus on the collateral reactions most commonly associated with this class of psychotropic drugs as a whole.
As we mentioned in the previous section, between the most common side effects of tricyclic antidepressants we found sedation and weight gain; both are due to the inhibition of histamine activity.
Blockade of acetylcholine receptors causes side effects such as constipation, urinary retention, dry mouth, blurred vision and memory problems . On the other hand, the inhibition of alpha-adrenergic receptors is related to alterations of the blood circulation, especially dizziness and orthostatic hypotension.
Among the serious adverse reactions to the consumption of tricyclics highlights the neuroleptic malignant syndrome , consisting of the appearance of respiratory, cardiac and muscular alterations that can cause coma and, in approximately one fifth of cases, death. This syndrome seems to be more frequent in people older than 50 years.
The high addictive potential of the tricyclics is also noteworthy, because pharmacological tolerance develops easily. The appearance of a severe withdrawal syndrome after abrupt cessation of consumption is also a consequence of tolerance. Likewise, the risk of overdose and suicide is strikingly high .
