Antidepressants are one of the most prescribed drugs in developed countries. There are many different types of antidepressants with different mechanisms of action. However, one thing is common – the drugs change the balance of neurotransmitters in the central nervous system.


Neurotransmitters are substances that help to transmit nerve impulses among the neurons and we suppose that the imbalance of neurotransmitter systems can cause occurrence of many psychiatric disorders. Antidepressants decrease anxiety, depression and fear. This makes them great in therapy of chronic depression, bipolar disorder and anxiety disorders (such as obsessive-compulsive disorder). Considering the extent of use of these drugs, we should be aware of their side effects. I shall mention the most used groups of antidepressants.


Tricyclic antidepressants

Drugs of this group affect repeated absorption of neurotransmitters such as norepinephrine and serotonin, thereby increasing their effect. This group includes for example substances such as amitriptyline or prothiaden.


The adverse effects may be relatively numerous and they are caused by the excessive neurotransmitter effect - dry mouth, palpitations, constipation, excessive sweating, drowsiness and weight gain. These side-effects usually disappear within a week of usage, but when they last, it is advisable to change the drugs for different type of antidepressants.


SSRI antidepressants

This group includes the most commonly used antidepressants. Their effect is focused mainly on the neurotransmitter serotonin. The drugs block its uptake and thus increase its effect. The commonly used substances are citalopram, escitalopram, fluoxetin, sertraline and paroxetine.


Side-effects include nausea, loss of appetite, diarrhea, decreased sexual libido, breast enlargement in men, troubles with ejaculation (including painful ejaculation), disturbed sleep pattern, excessive sweating and dry mouth. These effects usually last only for a short time and disappear in few weeks.

Very dangerous side effect is the so-called serotonin syndrome. It occurs due to excessive increase of the serotonin effect. It usually results from the combination of SSRI antidepressants with other compounds that increase the serotonin's effect (cocaine, amphetamines, opiates, LSD, monoamine oxidase inhibitors, certain prokinetics, etc.). The syndrome includes mental restlessness, palpitations, sweating, dilated pupils, hand tremor, high blood pressure and increased body temperature. The symptoms may develop relatively quickly and the syndrome can be easily fatal.


SARI antidepressants

Drugs in this group also increase the effects of serotonin. A typical example is substance known as trazodone. Possible side-effects include dry mouth and relatively dangerous priapism.


SNRI antidepressants

These antidepressants decrease repeated absorption of serotonin and norepinephrine. The most typical active substance is venlafaxine. Adverse effects of these drugs are similar to SSRI antidepressants (see above), including the serotonin syndrome.


Monoamine oxidase inhibitors

Monoamine oxidase is an enzyme, which causes breakdown of neurotransmitters such as epinephrine, norepinephrine and serotonin. Antidepressants of this group have the ability to block the function of monoamine oxidase, thereby reducing degradation of the mentioned neurotransmitters, causing their increased effectiveness.


Adverse effects may be very variable - loss of appetite, dizziness, insomnia and palpitations. An important side effect can be high blood pressure, which may be associated with headache, or chest pain. The risk of side effects increases in patients taking these drugs, who eat foods rich in the amino acid tyramine (red wine, bananas, cheese).


Jiri Stefanek, MD  Author of texts: Jiri Stefanek, MD
 Sources: basic text sources