SSRI Basics: How They Work

A straightforward explanation of what SSRIs are, how they work, and what to expect when taking them.

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Reviewed by the HeyPsych Medical Review Board

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Medical Review Board

Published: January 15, 2024

Last Updated: January 9, 2026

Last Reviewed: January 9, 2026

Article

7 min read

Overview

SSRIs (Selective Serotonin Reuptake Inhibitors) are the most commonly prescribed antidepressants. Despite their widespread use, many people don't understand how they work or what to expect. This guide breaks it down in plain language.

What Are SSRIs?

SSRI stands for Selective Serotonin Reuptake Inhibitor. Common SSRIs: • Fluoxetine (Prozac) • Sertraline (Zoloft) • Escitalopram (Lexapro) • Citalopram (Celexa) • Paroxetine (Paxil) • Fluvoxamine (Luvox) What they treat: • Major depression • Generalized anxiety disorder • Panic disorder • Social anxiety disorder • OCD • PTSD • Some eating disorders

How SSRIs Work

The simple version: SSRIs increase serotonin levels in your brain. Serotonin is a neurotransmitter (brain chemical) involved in mood regulation. The slightly more detailed version: • Your brain cells communicate using chemical messengers like serotonin • After serotonin delivers its message, it gets reabsorbed (reuptake) • SSRIs block this reabsorption • More serotonin stays available between brain cells • This eventually helps regulate mood Important reality check: We don't fully understand how SSRIs work. The "chemical imbalance" theory is oversimplified. SSRIs do increase serotonin, but the relationship between serotonin and mood is complex. What matters is that they help many people—we're still figuring out exactly why.

What to Expect: Timeline

Week 1-2: • Side effects may start immediately • Mood improvement: None yet (this is normal!) • Some people feel worse before better Week 2-4: • Side effects often decrease • You might notice small improvements in sleep, appetite, energy • Mood may still be low Week 4-6: • Mood improvements typically become noticeable • Full effects not reached yet • Side effects mostly resolved Week 6-12: • Full therapeutic effect develops • This is when you can truly evaluate if the medication is working Key takeaway: SSRIs require patience. If you're not better after 2 weeks, that's expected—not a sign of failure.

Common Side Effects

First 1-2 weeks (usually temporary): • Nausea • Headache • Increased anxiety or jitteriness • Sleep changes (insomnia or drowsiness) • Dizziness • Upset stomach Ongoing side effects (may persist): • Sexual dysfunction (decreased libido, difficulty orgasming) • Weight changes (usually gain) • Emotional blunting (feeling less intensely) • Vivid dreams • Fatigue Managing side effects: • Take with food if nauseous • Take at night if drowsy, morning if it interferes with sleep • Give it time—many side effects improve • Talk to your doctor about switching medications if side effects persist • Don't suffer in silence

Important Things to Know

SSRIs are not addictive: • You won't crave them or need increasing doses • But you shouldn't stop abruptly (see below) They're not "happy pills": • SSRIs don't make you artificially happy • They help regulate mood to a normal baseline • You still feel normal emotions Younger people need monitoring: • People under 25 have increased risk of suicidal thoughts when starting SSRIs • This doesn't mean SSRIs cause suicide • Close monitoring, especially in first weeks, is essential • Benefits usually outweigh risks, but awareness is important They work best with therapy: • Medication + therapy is more effective than either alone • SSRIs can make it easier to engage in therapy • Therapy provides skills medication can't

Stopping SSRIs

Never stop suddenly: • Can cause discontinuation syndrome • Symptoms: dizziness, nausea, fatigue, irritability, brain zaps (electric shock sensations) • Not dangerous, but very uncomfortable How to stop properly: • Taper gradually under doctor supervision • Usually over 2-4 weeks minimum • Slower is better, especially for Paxil and Effexor • Some people need months to taper When to consider stopping: • You've been stable for 6-12 months • Stressors that triggered depression/anxiety are resolved • You have good coping skills in place • In consultation with your doctor When to stay on: • Multiple previous episodes (3+) • Severe episodes • History of relapse when stopping • Ongoing risk factors • Some people need long-term treatment—and that's okay

What If They Don't Work?

Give it a full trial: • Adequate dose for 6-8 weeks minimum • Many people quit too early If one SSRI doesn't work: • Try a different SSRI (they're not all the same) • Try a different class (SNRI, bupropion, mirtazapine) • Consider augmentation (adding another medication) • Ensure diagnosis is correct • Evaluate for treatment-resistant depression approaches Response rates: • About 50-65% respond to the first SSRI tried • Another 15-25% respond to a second medication • Treatment-resistant doesn't mean untreatable—there are many options

Talking to Your Doctor

Questions to ask: • Why this specific SSRI? • What side effects should I watch for? • When should I call if I'm concerned? • How long before I should expect improvement? • What's the plan if this doesn't work? Be honest about: • All symptoms you're experiencing • Side effects, even embarrassing ones • Whether you're taking it as prescribed • Other medications or supplements • Alcohol or drug use • Suicidal thoughts (they need to know) Advocate for yourself: • If side effects are intolerable, speak up • If you don't feel heard, seek a second opinion • You're a partner in your treatment, not a passive recipient

Conclusion

SSRIs aren't perfect, but they're a valuable tool for many people struggling with depression and anxiety. They require patience, monitoring, and often some trial and error. Understanding how they work and what to expect helps you make informed decisions and stick with treatment long enough to know if it's working. If you're considering SSRIs or currently taking them, know that it's okay to have questions and concerns—your doctor should be willing to address them.