Antidepressants are medications primarily used to treat depression, though they can also help manage anxiety disorders and other conditions.
They work by altering brain chemistry, particularly neurotransmitters that regulate mood. While chemical imbalance is one theory behind depression, biological, psychological, and social factors also contribute.
There are several main classes of antidepressants: SSRIs, SNRIs, TCAs, and MAOIs. Atypical antidepressants are newer and don’t fit neatly into these categories.
Each type varies in how it works, its side effects, and what conditions it treats best. The choice of medication depends on symptom severity, other health conditions, and individual response.
This article is for informational and educational purposes only and is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician, therapist, or other qualified health provider with any questions you may have regarding a medical or mental health condition. Never disregard professional advice or delay in seeking it because of something you have read on this site.
How antidepressants work
Antidepressants work by acting on some part of neurotransmission within the brain.
Neurotransmission involves neurotransmitters, which are brain chemicals that travel around the brain and influence mood and behavior.
There are three main neurotransmitters that are influenced by antidepressants and are believed to be involved in the regulation of mood:
- Serotonin – this is believed to play a role in mood, feelings of happiness, appetite, and sleep.
- Dopamine – this plays a role in how we feel pleasure, motivation, rewards, arousal, and decision-making.
- Norepinephrine – this plays a role in regulating cognition, motivation, alertness, and regulating heart rate and blood pressure during stressful periods.
Types of antidepressants
Selective serotonin reuptake inhibitors (SSRIs)
Selective serotonin reuptake inhibitors (SSRIs) were developed in the 1980s and 1990s and work on affecting the use of the neurotransmitter serotonin in the brain.
SSRIs increase serotonin levels by blocking its reuptake into the presynaptic neuron. They are the most commonly prescribed antidepressants, used for depression, anxiety disorders, obsessive-compulsive disorder (OCD), posttraumatic stress disorder (PTSD), and panic disorder.
Common SSRIs include fluoxetine (Prozac), sertraline (Zoloft), and citalopram (Celexa). These medications are typically well tolerated and have fewer side effects than older classes.
Side effects may include headaches, nausea, insomnia, sexual dysfunction, and weight changes. Rarely, SSRIs may cause serotonin syndrome or increased suicidal thoughts in young people, especially when first starting treatment.
Monoamine oxidase inhibitors (MAOIs)
Monoamine oxidase inhibitors (MAOIs) were developed in the 1950s and were one of the earliest classifications of antidepressants.
MAOIs increase levels of serotonin, dopamine, and norepinephrine by blocking the enzyme monoamine oxidase.
MAOIs are primarily used for depression but also help relieve other conditions associated with depression or anxiety, such as agoraphobia, social phobia, and posttraumatic stress disorder.
Because of their interactions with foods high in tyramine (e.g., aged cheeses, cured meats, alcohol) and with other medications,
MAOIs can raise blood pressure to dangerous levels. They also carry a risk of serotonin syndrome when combined with certain drugs.
Tricyclics (TCAs)
Tricyclic antidepressants (TCAs) are known as a first generation of antidepressant drugs, invented after MAOIs.
TCAs were originally tested on people who had schizophrenia and became a popular antidepressant treatment in the 1960s.
TCAs block the reuptake of serotonin and norepinephrine. Though once widely used, they are now less common due to stronger side effects. TCAs are sometimes used for chronic pain, insomnia, migraines, OCD, and irritable bowel syndrome (IBS).
Examples include amitriptyline and nortriptyline. Side effects may include dizziness, fatigue, weight gain, dry mouth, nausea, sexual dysfunction, and irregular heartbeat.
TCAs may also elevate blood sugar and interact poorly with alcohol or certain emergency medications, making them unsuitable for some people with heart conditions or diabetes.
Serotonin-norepinephrine reuptake inhibitors
Serotonin-norepinephrine reuptake inhibitors (SNRIs) were introduced as a class of antidepressants in the mid-1990s.
SNRIs block the reuptake of both serotonin and norepinephrine (a chemical that plays a role in alertness, motivation, heart rate, and blood pressure).
They are used to treat depression, but can also be useful in treating other mental health conditions such as bipolar depression, obsessive-compulsive disorder (OCD), generalized anxiety disorder (GAD), attention deficit hyperactivity disorder (ADHD), chronic nerve pain, and fibromyalgia.
Common SNRIs include duloxetine (Cymbalta) and desvenlafaxine (Pristiq).
Side effects can include increased blood pressure, dizziness, nausea, muscle weakness, and agitation. Prolonged use may cause manic or hypomanic episodes, so they are often prescribed short-term or with caution in people with high blood pressure.
Atypical antidepressants
Atypical antidepressants are primarily newer types of medication that cannot be characterized under the branches of the other types of antidepressants.
Bupropion boosts dopamine and norepinephrine, making it helpful for depression. Mirtazapine is used to block the receptors of the hormone epinephrine (also known as adrenaline, a stress hormone). Agomelatine affects melatonin and serotonin, supporting circadian rhythm regulation.
Side effects vary but often include drowsiness or insomnia, weight gain, nausea, dry mouth, or sexual dysfunction. These medications may be used when standard options are ineffective or poorly tolerated.
Considerations
The best antidepressant depends on individual symptoms, medical history, and how the body responds.
It often takes 4 to 6 weeks to notice effects. SSRIs, for instance, may first improve energy or reduce anxiety before mood lifts.
If there’s no improvement after six weeks, a doctor may adjust the dosage or switch medications. Sometimes, combinations are used.
It’s crucial to take antidepressants consistently and under supervision, as high doses or drug interactions can trigger serotonin syndrome, a serious condition marked by confusion, high heart rate, and high blood pressure.
Stopping suddenly can lead to withdrawal symptoms like dizziness, tremors, or a return of depression. Tapering off slowly with medical guidance helps prevent this.
Do you need mental health support?
USA
Contact the National Suicide Prevention Lifeline for support and assistance from a trained counselor. If you or a loved one are in immediate danger: https://suicidepreventionlifeline.org/
1-800-273-8255
UK
Contact the Samaritans for support and assistance from a trained counselor: https://www.samaritans.org/; email jo@samaritans.org.
Available 24 hours a day, 365 days a year (this number is FREE to call):
116-123
Rethink Mental Illness: rethink.org
0300 5000 927
Further Reading
References
Institute for Quality and Efficiency in Health Care. (2015). Depression: How effective are antidepressants?
Krans, B. (2018, September 29). What Are MAO Inhibitors? Healthline. https://www.healthline.com/health/depression/what-are-mao-inhibitors
Sheffler, Z. M., & Abdijadid, S. (2020). Antidepressants . StatPearls [Internet].
