How antidepressants work: Pharmacology of anti-depressants

Antidepressants are the drugs used by psychiatrists for treating patients suffering from symptoms such as low mood, lack of self esteem, lack of interest, lethargy, excessive sadness, self regret, feeling of worthlessness…etc, which are collectively known as ‘depressive symptoms’. There are several antidepressants that have been used to treat these symptoms and although it may not bring about a lasting cure, in most instances it can manage the symptoms giving relief to the patient until they are able to cope with such symptoms on their own.

Commonly used antidepressants

Among the most common antidepressants that are being used, selective serotonin reuptake inhibitors (SSRI) and Tricyclic Antidepressants (TCA) are rather common with another category of drugs known as ‘MAO inhibitors’ or monoamine oxidase inhibitors. In order to understand how these antidepressants work, it is necessary to understand ‘what is the basis of depression’ among patients who are having symptomatic depressive illness.

The biochemical basis of depression

According to scientists, the reason for clinical depression could largely be due to the diminished levels of neurotransmitters (e.g serotonin and norephinephrin) within the ‘synaptic junctions’ existing between two neurons in the human brain. The neurons are the ones which transmit signals and the neurotransmitters are the chemical substance which carries a message from one neuron to the next. The transmitters are usually located at the end portion of the neuron known as the ‘synapse’. In response to a transmissible signal such as feeling of hunger, happiness, excitement…etc, the transmitters are released into the synaptic junction. It could them stimulate the receptors at the beginning of the next neuron which initiate a signal propagation. Following stimulating the receiving neuron, the neurotransmitters will again be re-absorbed into their original location in a process known as a ‘re-uptake’. As a result, these transmitters will be able to perform the same function over and over again.
In patients with depression, there seems to be an inherent deficiency of these neurotransmitters and therefore the signals may not be propagated effectively.

The basis of antidepressant actions

Thus, the actions of antidepressants would either be to increase the existence of adequate amount of neurotransmitters within the synaptic junction or else to prevent its natural destruction through a substance known as ‘monoamine oxidase’.

Specific actions of antidepressants

Thus, both SSRIs and TCAs will inhibit the re-uptake process and will make available more neurotransmitters within the synaptic junction. However, the MAO inhibitors will act in a different manner and will inhibit the action of Monoamine oxidase thus preventing the breakdown of the neurotransmitters thereby increasing its availability for normal signal transmission.
Although this is a simplified explanation of how antidepressants are functioning, it captures the most important aspect necessary in explaining the phenomenon.
Source:  http://pandula77.hubpages.com/hub/How-antidepressants-work-Pharmacology-of-anti-depressants