What does SSRI stand for?

SSRI stands for selective serotonin reuptake inhibitor. SSRIs increase the availability of serotonin in the brain by blocking its reabsorption into nerve cells. The relationship between this chemical effect and clinical improvement is more complicated than the early "chemical imbalance" framing suggested.

Which medications are SSRIs?

The SSRIs in common use are sertraline (Zoloft), escitalopram (Lexapro), fluoxetine (Prozac), paroxetine (Paxil), citalopram (Celexa), and fluvoxamine (Luvox). Vilazodone (Viibryd) and vortioxetine (Trintellix) act on serotonin in additional ways and are sometimes grouped with SSRIs and sometimes considered separately.

How long do SSRIs take to work?

Most people start to notice changes in two to six weeks, with sleep, appetite, and energy often shifting before mood does. Full effects often take eight to twelve weeks. The first SSRI tried is not always the right one.

What are the most common SSRI side effects?

Common side effects include nausea, headache, sleep changes, sexual side effects (reduced libido, delayed orgasm), and a temporary increase in anxiety in the first weeks. Most settle within a few weeks. New or worsening suicidal thoughts in the first weeks are a reason to call a prescriber the same day.

Do SSRIs cause weight gain?

Weight changes vary by medication and by person. Paroxetine has the strongest association with weight gain among SSRIs. Sertraline and escitalopram tend to be more weight-neutral. Bupropion, a different class of antidepressant, is less often associated with weight gain and is sometimes associated with weight loss. Choice of medication is individual. Discuss specific concerns with a prescriber.

Can SSRIs be stopped suddenly?

Stopping abruptly can cause a discontinuation syndrome (flu-like feelings, brain zaps, mood changes, sleep disruption) that lasts days to weeks. A taper supervised by a prescriber is the standard approach. Paroxetine and venlafaxine (an SNRI) tend to have the most pronounced discontinuation symptoms; fluoxetine, with its long half-life, tends to have the fewest.

SSRI | Depression Glossary

Quick definition: Selective serotonin reuptake inhibitor. A class of antidepressants that increases serotonin signaling.

Full clinical definition: SSRIs work by blocking the serotonin transporter (SERT), reducing the reuptake of serotonin into the presynaptic neuron and increasing the amount of serotonin available in the synaptic cleft. Examples include sertraline, escitalopram, fluoxetine, paroxetine, citalopram, and fluvoxamine. SSRIs are commonly first-line for adult depression because they are effective, generally well-tolerated, and have a wide therapeutic window.

Epidemiology: SSRIs are the most prescribed class of antidepressants in the United States. Antidepressant use among U.S. adults rose from 7.7 percent in 1999 to 13.2 percent in 2018 (NCHS Data Brief, 2020), and SSRIs account for the majority of those prescriptions.

Common uses: Depression, generalized anxiety disorder, panic disorder, social anxiety disorder, obsessive-compulsive disorder, post-traumatic stress disorder, premenstrual dysphoric disorder.

What it can feel like: For people who respond, the change is usually gradual. Sleep settles. Appetite returns to baseline. The mind stops cycling on the same negative thoughts. Crying spells become less frequent. Mood lifts last, often in the second month. Some people notice an early increase in anxiety or restlessness in the first one to two weeks, which usually settles.

How clinicians assess response: Symptoms are tracked over weeks, often with the PHQ-9 or a similar measure. A full trial is generally six to eight weeks at a therapeutic dose. Response is defined as at least a 50 percent reduction in symptom score. Remission is defined as few or no symptoms (PHQ-9 below 5).

Common side effects: Nausea (often early and short-lived), headache, sleep changes, sexual side effects, transient increase in anxiety in the first weeks. Sexual side effects are common across the class, with prevalence estimates of 40 to 65 percent in long-term users (Montejo et al., J Clin Psychiatry, 2001), and they persist throughout treatment for a substantial share of patients. Discontinuation symptoms (flu-like feelings, dizziness, electric-shock sensations) can occur if an SSRI is stopped abruptly after weeks of use, especially with shorter half-life drugs like paroxetine.

SSRIs at a glance

Drug	Typical adult range	Half-life	Notable for
Sertraline (Zoloft)	50 to 200 mg/day	About 26 hours	Broad use across depression and anxiety; favored in pregnancy and breastfeeding by many clinicians.
Escitalopram (Lexapro)	10 to 20 mg/day	27 to 32 hours	Clean side-effect profile; few drug interactions; often well tolerated.
Fluoxetine (Prozac)	20 to 80 mg/day	1 to 4 days (active metabolite up to 16 days)	Long half-life self-tapers; FDA approved for adolescents.
Citalopram (Celexa)	20 to 40 mg/day	About 35 hours	Dose-dependent QT prolongation; max 40 mg (20 mg if older than 60 or on CYP2C19 inhibitors).
Paroxetine (Paxil)	20 to 50 mg/day	About 21 hours	Higher rates of weight gain, sedation, anticholinergic effects, and discontinuation symptoms; generally avoided in pregnancy.
Fluvoxamine (Luvox)	50 to 300 mg/day	15 to 22 hours	FDA approved for OCD; numerous CYP1A2 and CYP2C19 interactions.

Information only, not a prescription. Dosing decisions belong with a prescriber.

Treatment implications: SSRIs are first-line for most adults with major depressive disorder per APA and NICE guidelines. Choice within the class is guided by side-effect profile, drug interactions, and prior response. Decisions about starting, changing, or stopping any antidepressant belong with a prescriber. A taper over weeks is preferred when stopping.

Related terms: Antidepressant. SNRI. Bupropion. Medication management.

Related articles: Treatment. Antidepressant comparison. SSRI side effects. Major depressive disorder.

Sources

Cipriani A, et al. Comparative efficacy and acceptability of 21 antidepressant drugs for the acute treatment of adults with major depressive disorder: a systematic review and network meta-analysis. Lancet. 2018.
American Psychiatric Association. Practice Guideline for the Treatment of Patients with Major Depressive Disorder.
NICE Guideline NG222.
Brody DJ, Gu Q. Antidepressant Use Among Adults: United States, 2015 to 2018. NCHS Data Brief No. 377. CDC, 2020.

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