SSRIs, or selective serotonin reuptake inhibitors, are a class of seven FDA-approved medications used primarily to treat depression and anxiety disorders. They are the most widely prescribed type of antidepressant, and each one works through the same basic mechanism but differs in how long it stays in your body, what conditions it’s approved for, and what side effects are most likely.
How SSRIs Work
Serotonin is a chemical messenger that carries signals between nerve cells in the brain. Normally, after serotonin delivers its signal, the sending cell reabsorbs it through a process called reuptake. SSRIs block that reabsorption, leaving more serotonin available in the gap between nerve cells. This increased serotonin activity is what helps improve mood, reduce anxiety, and ease obsessive thought patterns. The “selective” part of the name means these drugs primarily target serotonin rather than other brain chemicals.
The Seven FDA-Approved SSRIs
Each SSRI has a generic name and one or more brand names. Here are all seven currently approved in the United States:
- Fluoxetine (Prozac, Sarafem). The first SSRI to gain widespread use. It has the longest half-life of any SSRI, staying active in the body for one to four days, with its breakdown product lingering for up to 15 days. That long duration means missed doses are less likely to cause withdrawal symptoms, and it’s often the easiest SSRI to taper off. Approved for depression, OCD, panic disorder, bulimia, and certain forms of treatment-resistant depression. Starting dose is typically 20 mg daily, with a therapeutic range up to 60 mg for most people.
- Sertraline (Zoloft). One of the most commonly prescribed SSRIs overall. Approved for depression, OCD, panic disorder, PTSD, social anxiety disorder, and premenstrual dysphoric disorder. Its half-life is around 26 hours.
- Escitalopram (Lexapro). A newer, more refined version of citalopram (see below). It’s approved for depression and generalized anxiety disorder. The typical starting dose is 10 mg daily, with a range of 5 to 20 mg for most adults. Its half-life is roughly 36 hours.
- Citalopram (Celexa). Chemically related to escitalopram. Its half-life is also about 36 hours. One notable distinction: the maximum recommended dose is capped at 20 mg for people over 60, those with significant liver problems, or those taking certain interacting medications, due to heart rhythm concerns at higher doses.
- Paroxetine (Paxil, Paxil CR, Pexeva). Approved for depression, OCD, panic disorder, social anxiety disorder, generalized anxiety disorder, and PTSD. It has one of the shortest half-lives among SSRIs at about 21 hours, which makes it more likely to cause discontinuation symptoms if stopped abruptly.
- Fluvoxamine (Luvox, Luvox CR). Primarily prescribed for OCD rather than depression, though it works through the same serotonin mechanism as the others.
- Vilazodone (Viibryd). The newest addition to the SSRI family. It works on serotonin reuptake like the others but also partially activates a specific serotonin receptor, which may contribute to a somewhat different side effect profile.
Conditions SSRIs Treat
Depression is the most common reason SSRIs are prescribed, but the class covers a broad range of conditions. Depending on the specific drug, approved uses include generalized anxiety disorder, social anxiety disorder, panic disorder, obsessive-compulsive disorder, PTSD, premenstrual dysphoric disorder, and bulimia. Not every SSRI is approved for every condition. Fluoxetine and sertraline have the widest range of approved uses, while fluvoxamine is primarily an OCD medication and escitalopram is approved only for depression and generalized anxiety.
Prescribers sometimes use SSRIs for conditions beyond their formal approvals, including chronic pain syndromes, hot flashes during menopause, and certain eating disorders. This is common practice across medicine and doesn’t mean the use is experimental.
Common Side Effects
Most side effects show up in the first few weeks and fade as your body adjusts. Nausea is one of the earliest and most common, typically improving within a week or two. Fatigue, drowsiness, and sleep disruption are also frequent in the beginning. Some people experience the opposite: restlessness or a jittery, anxious feeling, particularly in the first days.
Sexual side effects are the most persistent problem with SSRIs as a class. These can include reduced sex drive, difficulty reaching orgasm, and erectile dysfunction. Unlike nausea or fatigue, sexual side effects often don’t resolve on their own and are one of the most common reasons people switch medications. Dry mouth, constipation, and changes in appetite or weight are also possible but tend to be milder.
Why Half-Life Matters
The half-life of a drug is how long it takes your body to clear half of it from your system. This has real practical consequences. Fluoxetine, with its multi-day half-life, builds up a reservoir in your body. If you miss a dose, you’re unlikely to notice. Paroxetine, with a half-life of just 21 hours, drops off much faster. Missing even a single dose of paroxetine can produce noticeable symptoms like dizziness, irritability, or electric shock-like sensations (sometimes called “brain zaps”).
This difference also matters when stopping the medication. Drugs with shorter half-lives generally need slower, more careful tapering schedules to avoid discontinuation symptoms.
Discontinuation Symptoms
Stopping an SSRI abruptly, or tapering too quickly, can cause a cluster of symptoms known as antidepressant discontinuation syndrome. These typically appear within a few days and can include flu-like achiness and fatigue, dizziness, nausea, vivid dreams or nightmares, burning or tingling sensations, and mood changes like irritability or anxiety. The experience is uncomfortable but not dangerous, and it resolves once the body adjusts or the medication is reintroduced.
Going off an SSRI safely is a gradual process. Your prescriber will create a tapering plan specific to your drug and dose, which can take weeks or sometimes months. Paroxetine and fluvoxamine, with their shorter half-lives, are generally the most challenging to discontinue. Fluoxetine is the easiest because its long-acting metabolite essentially tapers itself.
Serotonin Syndrome
A rare but serious risk with any serotonin-affecting drug is serotonin syndrome, which happens when serotonin levels climb too high. This almost always involves combining two or more serotonin-boosting substances, whether prescription medications, supplements like St. John’s wort, or certain migraine drugs. Symptoms appear within minutes to hours and include rapid heartbeat, high blood pressure, fever, agitation, muscle twitching, diarrhea, and loss of coordination. Severe cases can be life-threatening. The key to prevention is making sure every prescriber knows all the medications and supplements you take.
The FDA Black Box Warning
All SSRIs carry a boxed warning, the FDA’s most serious label alert, about an increased risk of suicidal thoughts and behavior in children and adolescents. This doesn’t mean SSRIs cause suicide. It means that during clinical trials, young people on antidepressants showed higher rates of suicidal thinking compared to those on a placebo. The risk is highest in the first few months of treatment or when doses change. For this reason, younger patients are monitored closely during early treatment, and families are advised to watch for unusual mood changes, agitation, or withdrawal.