Antidepressants are among the most prescribed medications in the United States. Per CDC data, approximately 13.2% of U.S. adults reported using antidepressants in the past 30 days. Despite this widespread use, substantial confusion exists about how antidepressants work, what they treat, and what to expect.
This article addresses SSRIs and SNRIs — the two most commonly prescribed antidepressant classes — covering FDA-approved indications, mechanism of action, expected effects, and side effect profiles. The goal is informed patient engagement with antidepressant treatment decisions.
Selective Serotonin Reuptake Inhibitors (SSRIs)
Mechanism
SSRIs inhibit reuptake of serotonin at the synaptic cleft, increasing serotonergic neurotransmission. They have minimal effect on other neurotransmitter systems, accounting for their favorable side effect profile relative to older antidepressants like tricyclics.
Common SSRIs and FDA approvals
- Sertraline (Zoloft) — Major depression, panic disorder, OCD, PTSD, social anxiety, PMDD
- Escitalopram (Lexapro) — Major depression, generalized anxiety disorder
- Fluoxetine (Prozac) — Major depression, OCD, bulimia, panic disorder, PMDD, treatment-resistant depression (with olanzapine)
- Paroxetine (Paxil) — Major depression, OCD, panic disorder, social anxiety, GAD, PTSD, PMDD
- Citalopram (Celexa) — Major depression (dose-limited due to QTc concerns)
- Fluvoxamine (Luvox) — OCD (primary indication in U.S.)
Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs)
Mechanism
SNRIs inhibit reuptake of both serotonin and norepinephrine. The dual mechanism produces somewhat different effect profile than pure SSRIs.
Common SNRIs and FDA approvals
- Venlafaxine (Effexor XR) — Major depression, GAD, panic disorder, social anxiety
- Duloxetine (Cymbalta) — Major depression, GAD, fibromyalgia, neuropathic pain, chronic musculoskeletal pain
- Desvenlafaxine (Pristiq) — Major depression
- Levomilnacipran (Fetzima) — Major depression
What to Expect During Treatment
Timeline
- Weeks 1-2: Side effects often peak; therapeutic effects minimal
- Weeks 2-4: Side effects often improve; initial therapeutic effects may emerge
- Weeks 4-8: Substantial therapeutic response typically develops
- Weeks 8-12: Full response often present at adequate dose
Common early side effects (often resolve)
- Nausea and GI symptoms — often resolve within 1-2 weeks
- Headache
- Initial activation or jitteriness
- Sleep changes — insomnia or somnolence
- Vivid dreams
- Fatigue
Common persistent side effects
- Sexual dysfunction — Per published studies summarized by Harvard Health Publishing, sexual side effects (decreased libido, delayed orgasm, anorgasmia, erectile dysfunction) occur in a substantial proportion of patients on SSRIs — published estimates range widely (35-80%) depending on assessment methodology and population
- Weight changes — Some patients gain weight (more common with paroxetine, mirtazapine); some lose weight initially
- Emotional blunting — Some patients report reduced emotional range
- Sweating — Particularly with SNRIs (venlafaxine, duloxetine)
Persistent sexual dysfunction
Per Australian TGA and other international regulatory bodies, SSRIs and SNRIs now carry warnings about potential persistent sexual dysfunction after discontinuation in some patients (post-SSRI sexual dysfunction, or PSSD). The exact prevalence is not well-established; published estimates vary widely.
Serious Considerations
Suicidality warning
SSRIs and SNRIs carry an FDA black box warning regarding increased suicidal ideation in patients under 25. Risk-benefit analysis remains favorable in this age group for most patients — but close monitoring during initial treatment is appropriate.
Serotonin syndrome
Rare but serious — typically from drug interactions (especially with MAOIs, tramadol, triptans, lithium, St. John’s wort). Symptoms include agitation, sweating, tremor, hyperreflexia, autonomic instability.
Discontinuation syndrome
Abrupt discontinuation — particularly of short half-life SSRIs/SNRIs (paroxetine, venlafaxine, duloxetine) — produces discontinuation symptoms including dizziness, “brain zaps,” GI symptoms, anxiety, flu-like symptoms. Slow tapering prevents most cases.
Bipolar considerations
In patients with undiagnosed bipolar disorder, antidepressants can precipitate manic or hypomanic episodes. Careful screening for bipolar history is important before antidepressant initiation.
Pregnancy considerations
Most SSRIs are relatively well-studied in pregnancy. Risk-benefit analysis involves balancing risks of untreated depression against medication risks. Decisions should involve discussion with prescriber and obstetric care.
Source: APA practice guidelines and STAR*D trial data.
Premature discontinuation
Many patients stop antidepressants during the first weeks when side effects peak — before therapeutic effect fully emerges.
Honest expectations and management
Dr. Farkas prepares patients for expected side effects, provides specific management strategies, and supports through the adjustment period.
Successful treatment
With appropriate side effect management and adequate trial duration, most patients tolerate antidepressants well enough to achieve full therapeutic benefit.
Common Questions About Antidepressants
Will antidepressants change my personality?
No. Antidepressants reduce depression and anxiety symptoms — not personality, interests, or values. Most patients describe being more themselves after effective treatment, not less.
Are antidepressants addictive?
SSRIs and SNRIs aren’t addictive — they don’t produce craving or compulsive use. However, abrupt discontinuation can produce discontinuation symptoms, which is different from addiction. Slow tapering prevents most discontinuation symptoms.
What about sexual side effects?
Common with SSRIs and SNRIs. Management options include dose adjustment, switching to bupropion (typically no sexual side effects), adding bupropion to current medication, sildenafil/tadalafil for some patients, or timing strategies. See our related articles on antidepressant side effects and major depression.
How long should I take antidepressants?
For first depressive episodes, typically 6-12 months after remission. For recurrent depression, longer-term treatment often produces better outcomes. For anxiety disorders, treatment duration varies based on condition and response. Decisions are individualized.