SSRIs

A teenager starting fluoxetine whose parent asks "why does the label warn about suicide?" deserves a precise answer — and so does the NCLEX.

SSRIs carry a black box warning for increased suicidality in children, adolescents, and young adults under 25, especially during the first 1–4 weeks when energy returns before mood lifts. Monitor closely at initiation and every dose change. Common adverse effects include GI upset (nausea, diarrhea), sexual dysfunction, insomnia or drowsiness, weight changes, and CNS activation or agitation. Serotonin syndrome is the life-threatening emergency: it occurs when serotonin accumulates excessively, typically from combining an SSRI with another serotonergic agent (MAOIs, tramadol, triptans, St. John's wort, linezolid). The classic triad is altered mental status (agitation, confusion), autonomic instability (hyperthermia, tachycardia, diaphoresis), and neuromuscular hyperactivity (clonus, hyperreflexia, tremor). Onset is rapid — often within hours. Treatment is discontinuation of the offending agents and supportive care; cyproheptadine is the serotonin antagonist used. A washout period is required between MAOIs and SSRIs — at least 14 days in most cases, though fluoxetine requires a 5-week washout before starting an MAOI due to its long-acting metabolite. Abrupt discontinuation causes SSRI discontinuation syndrome — dizziness, irritability, paresthesias ("brain zaps"), flu-like symptoms — so taper gradually.

Key Distinctions

Don't confuse serotonin syndrome (hyperthermia, clonus, rapid onset) with neuroleptic malignant syndrome (lead-pipe rigidity, slower onset, tied to antipsychotics). Students often mistake the black box warning as a contraindication — it's a monitoring mandate, not a prohibition. Discontinuation syndrome is uncomfortable but not dangerous; serotonin syndrome is a medical emergency requiring immediate intervention.

Clinical Pearl

Serotonin syndrome = HOT and TWITCHY (hyperthermia, clonus, hyperreflexia). NMS = HOT and STIFF (rigidity, elevated CK). The movement pattern tells you which one.

MOA & Clinical Use

SSRIs — fluoxetine, sertraline, paroxetine, citalopram, escitalopram, fluvoxamine — work by selectively blocking the reuptake of serotonin at the presynaptic neuron. This increases serotonin availability in the synaptic cleft, but the clinical response lags 4-6 weeks because downstream receptor sensitivity must gradually adjust. This delay is critical: the patient may feel more energized before mood improves, which temporarily increases suicide risk in the early weeks. An FDA Black Box Warning requires monitoring for increased suicidality in patients under age 25, especially during the first weeks of therapy. SSRIs are first-line because they are selective — they leave norepinephrine and dopamine reuptake largely untouched, which means fewer cardiovascular and anticholinergic effects compared to TCAs or MAOIs. Indications extend well beyond major depressive disorder: generalized anxiety disorder, panic disorder, OCD, PTSD, social anxiety disorder, PMDD, and bulimia nervosa (fluoxetine specifically). Fluoxetine has the longest half-life (~4-6 days for its active metabolite norfluoxetine), making it the most forgiving if a dose is missed and the least likely to cause discontinuation syndrome. Sertraline is generally preferred in pregnancy due to a comparatively favorable safety profile. Paroxetine carries the highest anticholinergic load among SSRIs and is avoided in pregnancy due to documented risk of fetal cardiac malformations.

Key Distinctions

Don't confuse SSRI selectivity with safety — selective for serotonin doesn't mean side-effect-free; it means fewer off-target receptor effects than TCAs. Students often think therapeutic onset matches when the patient starts the medication; the 4-6 week delay is the most tested timeline in this category. Fluoxetine's long half-life is protective against discontinuation syndrome, while paroxetine's short half-life makes it the highest risk for it.

Clinical Pearl

Think of SSRIs as serotonin's bouncer — they block reuptake so serotonin stays in the club longer. But the mood doesn't lift until the club renovates, which takes 4-6 weeks.