There are many categories of antidepressants which are used to treat various depressive disorders. Each category medication has its own specific action on depression and function. The categories of antidepressants are TCAs, MAOIs, SSRIs, SNRIs, NDRIs, and combined inhibitors and blockers.

Tricyclic Antidepressants (TCAs)

Nature and Working of TCAs: One category of antidepressants is called tricyclic because of their chemical structure. These tricyclic antidepressants (TCAs) are very useful medications for treatment of panic disorder and depressive symptoms such as gloominess, pessimism, irritability, etc.

Serotonin, norepinephrine and dopamine are neurotransmitters in central nervous system that help in communication between nerve cells. These chemicals reside in the synaptic space and act as medium for communication between nerve ends. The sending nerve secretes neurotransmitters. And a receiving nerve will have receptors to receive communication through these neurotransmitters. The secreting nerve of these chemicals also re-absorbs them to maintain balance in the system. As a consequence, the levels of these neurotransmitters go down. When the levels of these neurotransmitters are decreased, it will lead to a condition of gloominess and sadness. These are the symptoms of depressive disorder. TCAs act in strengthening the supply of these chemicals which help in reducing depression. Some of the TCA medications are: Amitriptyline, clomipramine, amoxapine, desipramine, doxepin, imipramine, nortriptyline, protriptyline, dothiepin, trimipramine, etc.

Precautions with TCAs: TCAs should not be administered to people who have glaucoma, prostate problems, and certain heart diseases. Monitoring is needed with diabetic problems, thyroid problems, urinary retention, and also seizures.

Monoamine Oxidase Inhibitors (MAOIs )

Nature and Working of MAOIs: The neurotransmitters that we have discussed above are known as monoamines. While these neurochemicals assist as messengers of information between nerve ends, they also get metabolized by an enzyme called monoamine oxidase. This is where monoamine oxidase inhibitors come in where they retard the action of monoamine oxidase in destroying neurotransmitters. This will help in increasing the levels of neurotransmitters which, in turn, help in reducing the symptoms of depression. The MAOI medications are p henelzine, tranylcypromine, isocarboxazid, selegiline, moclobemide, cimetidine, etc.

Precautions with MAOIs: The enzyme, monoamine oxidase, destroys another amine also, called tyramine, along with serotonin, norepinephrine, and dopamine. This tyramine is responsible for blood pressure levels. When monoamine oxidase is inhibited, tyramine levels go up, resulting in sudden increase in blood pressure levels. This may prove fatal.

Caution: Seasoned cheese, chicken liver, pickled herring, broad-bean pods, etc., contain high levels of tyramine. Avoid these food items when on medication with MAOIs.

Selective Serotonin Reuptake Inhibitors (SSRIs)

Nature and Working of SSRIs: SSRIs are medications developed after MAOIs. As the name suggests, they selectively block re-absorbance of serotonin neurotransmitters so that their levels increase, resulting in the reduction of depressive symptoms. Citalopram, escitalopram, fluoxetine, paroxetine, sertraline, etc. are some of the SSRIs.

Precautions with SSRIs: People with uncontrolled epilepsy should not be treated with SSRIs. People under 18 and suffering from major depressive disorder, should not be medicated with SSRIs. Caution is also necessary while undergoing electroconvulsive therapy (ECT). SSRIs are a strict no-no during pregnancy and breastfeeding.

Serotonin and norepinephrine reuptake inhibitors (SNRIs)

Nature and Working of SNRIs: SNRIs are another category of antidepressant drugs that help in increasing the levels of serotonin and norepinephrine by retarding their re-absorption. Venlafaxine, duloxetine, etc. are some of SNRIs.

Precautions with SNRIs: People who are under treatment with MAOIs should not take SNRIs because the combination will result in serotonin syndrome. The syndrome occurs when serotonin levels increase abnormally due to the combined effect, which may prove fatal.

Norepinephrine and dopamine reuptake inhibitors (NDRIs)

Nature and Working of NDRIs: NDRIs are a category of antidepressant drugs which aid in increasing norepinephrine and dopamine levels in the brain by retarding their re-absorption into cells. Bupropion is the medication presently available. Radafaxine is still in clinical trials.

Precautions with NDRIs: These may affect blood pressure levels suddenly and may prove life-threatening sometimes.

Combined reuptake inhibitors and receptor blockers

Nature and Working of these Drugs: These are dual-action antidepressant drugs. They not only inhibit re-absorption of neu0.rotransmitters, but also block nerve cell receptors. This combined activity will decrease depression. Trazodone, Nefazodone, Maprotiline, etc. are some of these combined antidepressants.

Precautions with combined Drugs: Trazodone may affect a person with priapism, a condition where painful erections will be persistent without any reason. Sometimes surgical intervention may be needed to correct the situation. In some cases, nefazodone may severely affect liver.