Understanding Antidepressants and How They Work
Antidepressants are prescription medications used to treat major depressive disorder, anxiety disorders, chronic pain, and other conditions [1.6.1, 1.6.2]. They function by altering the levels of neurotransmitters—chemicals used by brain cells to communicate—which can help relieve symptoms of depression [1.2.7]. According to the National Institute of Mental Health (NIMH), these medications usually take 4 to 8 weeks to become fully effective [1.6.4, 1.6.6].
The choice of antidepressant depends on several factors, including a person's specific symptoms, other health conditions, potential side effects, and whether a close relative responded well to a particular medication [1.5.1, 1.5.4].
Selective Serotonin Reuptake Inhibitors (SSRIs)
SSRIs are the most commonly prescribed class of antidepressants because they are effective and generally have fewer side effects than older medications [1.2.7]. They work by specifically blocking the reabsorption (reuptake) of serotonin in the brain, making more of this neurotransmitter available [1.2.7, 1.2.8].
Examples of SSRIs:
- Citalopram (Celexa) [1.2.2, 1.2.3]
- Escitalopram (Lexapro) [1.2.2, 1.2.3]
- Fluoxetine (Prozac) [1.2.2, 1.2.3]
- Paroxetine (Paxil, Pexeva) [1.2.2, 1.2.5]
- Sertraline (Zoloft) [1.2.2, 1.2.3]
- Vilazodone (Viibryd) [1.2.2]
Common side effects can include nausea, headache, insomnia, weight changes, and sexual dysfunction [1.3.3, 1.3.7]. A rare but serious condition called serotonin syndrome can occur if SSRIs are taken with other medications that also increase serotonin levels [1.6.1].
Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs)
SNRIs function by blocking the reuptake of both serotonin and norepinephrine [1.2.7]. They are effective for depression and are also used for anxiety disorders and some forms of chronic pain [1.5.1].
Examples of SNRIs:
- Venlafaxine (Effexor XR) [1.2.7]
- Desvenlafaxine (Pristiq) [1.2.4]
- Duloxetine (Cymbalta) [1.2.4]
- Levomilnacipran (Fetzima) [1.2.4]
Side effects are similar to SSRIs but can also include increased sweating, dizziness, and dry mouth [1.3.9]. Some SNRIs may increase blood pressure [1.5.7].
Tricyclic Antidepressants (TCAs)
TCAs were among the first antidepressants developed [1.2.7]. They are effective but are prescribed less frequently today due to a higher risk of side effects [1.2.7]. They work by blocking the reuptake of serotonin and norepinephrine, but they also affect other neurotransmitters, leading to more side effects [1.2.7].
Examples of TCAs:
- Amitriptyline [1.2.3]
- Nortriptyline (Pamelor) [1.2.3]
- Imipramine (Tofranil) [1.2.3]
- Doxepin [1.2.3]
- Clomipramine (Anafranil) [1.2.2]
- Desipramine (Norpramin) [1.2.2]
Common side effects include dry mouth, blurred vision, constipation, drowsiness, and weight gain [1.3.6].
Monoamine Oxidase Inhibitors (MAOIs)
MAOIs are an older class of antidepressants that work by inhibiting monoamine oxidase, an enzyme that breaks down neurotransmitters like serotonin, norepinephrine, and dopamine [1.2.7]. They are highly effective but require strict dietary restrictions to avoid serious complications, such as dangerously high blood pressure when combined with foods containing tyramine (e.g., aged cheeses, certain meats) [1.2.7, 1.3.4].
Examples of MAOIs:
- Phenelzine (Nardil) [1.2.6]
- Tranylcypromine (Parnate) [1.2.6]
- Isocarboxazid (Marplan) [1.2.6]
- Selegiline (Emsam), available as a skin patch [1.2.6]
Atypical Antidepressants
This category includes medications that don't fit into the other classes and have unique mechanisms of action [1.2.7].
Examples of Atypical Antidepressants:
- Bupropion (Wellbutrin): A norepinephrine-dopamine reuptake inhibitor (NDRI) that is less likely to cause sexual side effects or weight gain [1.2.7, 1.5.1]. It is also used to help with smoking cessation [1.2.7].
- Mirtazapine (Remeron): This medication can cause drowsiness and is often taken at bedtime [1.2.7]. It may also lead to weight gain [1.3.5].
- Trazodone (Desyrel): Like mirtazapine, it often causes drowsiness and is prescribed for insomnia [1.2.7]. A rare but serious side effect is priapism [1.2.7].
- Vortioxetine (Trintellix): A serotonin modulator that acts as both an inhibitor and a receptor modulator [1.2.2].
Comparison of Antidepressant Classes
| Class | Mechanism of Action | Common Examples | Common Side Effects |
|---|---|---|---|
| SSRIs | Blocks reuptake of serotonin [1.2.7] | Fluoxetine (Prozac), Sertraline (Zoloft), Escitalopram (Lexapro) [1.2.2] | Nausea, insomnia, sexual dysfunction, headache [1.3.7] |
| SNRIs | Blocks reuptake of serotonin and norepinephrine [1.2.7] | Venlafaxine (Effexor), Duloxetine (Cymbalta) [1.2.7] | Nausea, dizziness, sweating, dry mouth, increased blood pressure [1.3.9] |
| TCAs | Blocks reuptake of serotonin and norepinephrine; affects other receptors [1.2.7] | Amitriptyline, Nortriptyline (Pamelor) [1.2.3] | Dry mouth, constipation, blurred vision, drowsiness, weight gain [1.3.6] |
| MAOIs | Inhibits monoamine oxidase enzyme [1.2.7] | Phenelzine (Nardil), Selegiline (Emsam) [1.2.6] | Dizziness, insomnia; requires strict dietary restrictions [1.3.4, 1.2.7] |
| Atypicals | Varies by medication [1.2.7] | Bupropion (Wellbutrin), Mirtazapine (Remeron), Trazodone [1.2.7] | Varies; can include sedation (Mirtazapine, Trazodone) or activating effects (Bupropion) [1.2.7] |
Conclusion
Many types of antidepressants are available, each with a different mechanism, benefit, and side effect profile. The selection process is highly individualized and involves careful consideration by a healthcare provider of the patient's symptoms, medical history, and other medications [1.5.1, 1.5.2]. Finding the right medication can sometimes be a process of trial and error, but open communication with a doctor is key to finding an effective treatment [1.5.2]. It's crucial to take medication as prescribed and to never stop taking an antidepressant abruptly, as this can cause discontinuation syndrome [1.3.1, 1.3.2].
For more information, you can visit the National Institute of Mental Health (NIMH) page on Mental Health Medications.
