Paxil Side Effects: What to Expect and When to Call Your Doctor

Starting a new antidepressant can be uncertain territory. You might feel better quickly, or side effects might appear first. This guide covers everything you need to know about Paxil (paroxetine) side effects — what's common, what's serious, and when to pick up the phone and call your doctor.

Common Paxil Side Effects

Most patients experience one or more of these common side effects, especially during the first few weeks of treatment:

Nausea: Very common in the first 1–2 weeks. Taking paroxetine with food can help. Usually resolves on its own as your body adjusts.

Drowsiness or fatigue: Paroxetine can cause sedation, particularly at higher doses. Some patients prefer evening dosing to reduce daytime sleepiness.

Dry mouth: Related to paroxetine's mild anticholinergic properties. Staying hydrated and sugar-free gum can help.

Sweating: Increased sweating, sometimes significantly so, is a common paroxetine side effect. Night sweats are frequently reported.

Constipation: Also related to anticholinergic activity. Increasing fiber and water intake usually helps.

Insomnia or sleep disturbances: Some patients experience difficulty falling or staying asleep, particularly with morning dosing.

Dizziness: Particularly upon standing (orthostatic hypotension). Move slowly when transitioning from sitting or lying to standing.

Headache: Frequently reported in the first 1–2 weeks. Usually self-limited.

Sexual Side Effects: The Biggest Concern for Many Patients

Paroxetine has the highest rate of sexual dysfunction among SSRIs — affecting an estimated 40–70% of patients taking it long-term. This includes:

Decreased libido (reduced sex drive) in both men and women

Anorgasmia or delayed orgasm in women

Delayed or inhibited ejaculation in men

Erectile dysfunction in men

In some patients, sexual dysfunction may persist even after stopping paroxetine — a condition known as Post-SSRI Sexual Dysfunction (PSSD). The European Medicines Agency and Health Canada have both recommended that paroxetine's labeling warn of this risk. If sexual side effects are problematic, discuss options with your doctor — these may include dose reduction, switching medications, or adding another agent.

Weight Gain

Paroxetine is associated with more weight gain than other SSRIs, particularly with long-term use. In clinical practice, patients commonly report gaining 5–15 pounds over the course of a year or more. This is thought to be related to appetite changes and metabolic effects, not water retention. If weight gain becomes significant, discuss this with your prescriber.

Serious Side Effects — When to Seek Immediate Care

While serious side effects are less common, they can occur and require prompt medical attention:

Serotonin syndrome: A potentially life-threatening reaction when serotonin levels become too high. Symptoms include agitation, confusion, rapid heart rate, high blood pressure, dilated pupils, and muscle rigidity or twitching. Seek emergency care immediately. Risk is highest when combining paroxetine with other serotonergic drugs (MAOIs, tramadol, triptans, etc.).

Increased suicidal thoughts (especially in young adults): Paroxetine carries an FDA black box warning for increased suicidal thinking in children, adolescents, and young adults under 25. Monitor closely in the first few weeks and after dose changes. Call 988 (Suicide & Crisis Lifeline) if you or someone you know is in crisis.

Hyponatremia (low sodium): Can cause headache, confusion, weakness, and seizures. More common in elderly patients and those on diuretics. Signs include severe headache, confusion, or weakness.

Mania or hypomania: In patients with undiagnosed bipolar disorder, SSRIs can trigger a manic episode. Signs include decreased need for sleep, racing thoughts, grandiosity, and reckless behavior. Contact your prescriber immediately.

Bleeding problems: Paroxetine can increase bleeding risk by reducing platelet function. This is especially relevant if you take aspirin, NSAIDs (ibuprofen, naproxen), or blood thinners. Watch for unusual bruising or prolonged bleeding.

Discontinuation Syndrome: What Happens If You Stop Suddenly

Paroxetine has the highest discontinuation syndrome risk of all SSRIs. Never stop paroxetine abruptly. Symptoms of discontinuation include:

"Brain zaps" (brief electric shock-like sensations in the head)

Dizziness and nausea

Irritability and anxiety

Flu-like symptoms (sweating, chills, muscle aches)

Insomnia and vivid dreams

If you're stopping paroxetine, work with your doctor to gradually taper the dose — typically reducing by 10 mg every 1–2 weeks. If your pharmacy is out of stock and you're at risk of missing doses, contact your prescriber right away.

The Bottom Line

Many paroxetine side effects are manageable and improve over the first few weeks of treatment. The most important things to watch for are signs of serotonin syndrome, suicidal thoughts, and any symptoms of hyponatremia — these require immediate medical attention. Learn more about paroxetine's drug interactions in our guide to Paxil drug interactions. And if supply is a concern, medfinder can help you find paroxetine in stock at pharmacies near you.