The most common side effects are anxiety and nervousness (reported by 5–13% of people taking various SSRIs), tremor (5–14%), trouble sleeping (2–8%), tiredness or weakness (4–15%), nausea (11–26%), diarrhea (11–26%), constipation (1–8%), loss of appetite (3–18%), weight loss (1–13%), dry mouth (10–22%), headache (1–5%), sweating (5–9%), trouble urinating (1–2%), and decreased sexual ability (8–15%). Many of these problems diminish or disappear as the body adjusts to the drug and do not require medical treatment unless they interfere with normal activities. Persistent problems, such as sexual dysfunction, should be discussed with the doctor.

More serious side effects are possible, but extremely rare. People taking SSRIs who notice unusual joint or muscle pain; breathing problems; chills or fever; excessive excitement, fast talking, or actions that are out of control; or mood swings should contact their doctors. People who develop skin rashes or hives after taking an SSRI should stop taking the medication and contact their doctors as soon as possible. Other rare side effects may occur. Anyone who has unusual symptoms after taking an SSRI should get in touch with his or her doctor.

Side effects may continue for some time after treatment with this medicine ends. How long the effects continue depends on how long the drug was taken and how much of it was used. In most cases, doctors recommend that patients taper off SSRIs rather than abruptly stopping them, because of the risk of developing a condition known as SSRI discontinuation syndrome. This syndrome can mimic serious illness. People who experience agitation, confusion, or restlessness; dizziness or lightheadedness; vision problems; tremor; sleep problems; unusual tiredness or weakness; nausea and vomiting or diarrhea; headache; excessive sweating; runny nose; or muscle pain for more than a few days after stopping or tapering an SSRI should consult their doctors.