Antidepressant Medications

Introduction to Antidepressants

In addition to antipsychotics and antianxiety drugs, there are four major classes of antidepressants. St. John’s Wort is another herbal antidepressant.

Antidepressants increase neurotransmitters in the brain.

Antidepressants work on norepinephrine, serotonin, or both. Most patients with major depressive disorder tend to be low on norepinephrine and serotonin. Antidepressants increase the brain’s access to those two neurotransmitters.

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Selective Serotonin Receptor Inhibitors

Selective serotonin reuptake inhibitors (SSRIs) are the most widely prescribed class of antidepressants and include drugs such as Zoloft or Lexapro. SSRIs mostly increase the brain’s access to serotonin.

Increasing levels of serotonin can help improve symptoms of depression.

Gastrointestinal upset is the most common side effect, so providers should instruct patients to take with food to ease symptoms. Diarrhea is another side effect that improves over time as the body acclimates to the drug.

The most severe side effect is serotonin syndrome. It’s a potential SSRI complication wherein the brain accesses too much serotonin. The patient may exhibit agitation, tremors, diaphoresis-dilated pupils, and tachycardia. Providers must watch for these side effects.

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Serotonin-Norepinephrine Reuptake Inhibitors

Serotonin-norepinephrine reuptake inhibitors (SNRIs) include drugs such as Pristiq and Cymbalta. They increase the brain’s access to both serotonin and norepinephrine.

Providers must watch for hypertension when administering any drug that increases the availability or amount of norepinephrine, a powerful vasoconstrictor.

Providers should not mix SNRIs with any other type of antidepressants, such as tricyclic or Monoamine oxidase inhibitors (MAOI). It puts the patient at significant risk for hypertension and hypertensive crisis.

Tricyclic Antidepressant

Tricyclic antidepressants are one of the older classes of antidepressants and include “-ine” drugs such as amitriptyline. Tricyclic antidepressants have an anticholinergic effect. They “dry up” a patient.

A tricyclic antidepressant features three cyclic rings in the drug structure.

Tricyclic side effects mimic those of anticholinergics. They include dry eyes, dry mouth, and constipation. Orthostatic hypotension is prominent with tricyclic antidepressants. Providers must tell patients to get up slowly from sitting to standing when they first start taking the drug. Otherwise, they might experience orthostatic hypotension or syncope.

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Monoamine Oxidase Inhibitors

Monoamine oxidase inhibitors (MAOIs) were the first class of developed and marketed antidepressants and include drugs like phenelzine. Safer, better medications have developed over the years. MAOIs include some severe side effects.

People who take MAOIs need to avoid fermented foods like wine and cheese.

The biggest risk MAOIs pose is hypertensive crises. Patients on MAOIs can’t consume a large amount of a compound called tyramine, found in foods, such as wine, cheese, some types of chocolate, and many fermented foods. Providers must inform patients of the risks.

Patients taking MAOIs can’t take SSRIs because it increases the risk for serotonin syndrome. Providers should generally avoid combining different antidepressant medication classes because it increases the medications’ risks.

St. John’s Wort

St. John’s Wort is an herbal remedy patients can take for depression. It’s known to have antidepressant properties. Patients should not take it with other antidepressants because it severely increases the risk for serotonin syndrome.

Summary

The four major classes of antidepressant drugs are selective serotonin receptor inhibitors, serotonin-norepinephrine receptor inhibitors, tricyclic antidepressants, and monoamine oxidase inhibitors. St. John’s Wort is another herbal remedy. 

They all enhance the brain’s access to the neurotransmitters norepinephrine and serotonin. They have varying side effects, so providers must educate patients on them. Providers must also watch for serotonin syndrome.