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

Fluconazole (Diflucan) is generally well tolerated, particularly when used for short courses to treat common infections like vaginal yeast infections or oral thrush. However, like all medications, it carries the risk of side effects — ranging from mild GI upset to rare but serious conditions requiring immediate medical attention.

Understanding what side effects to expect — and which symptoms require urgent attention — helps you take fluconazole safely and confidently.

Common Side Effects of Fluconazole (≥1% of Patients)

The following side effects occur in at least 1% of patients taking fluconazole:

• Nausea: The most commonly reported side effect. Taking fluconazole with food may help, though it can be taken with or without food.
• Headache: Usually mild and temporary; typically resolves without treatment.
• Dizziness: Avoid driving or operating heavy machinery until you know how fluconazole affects you.
• Abdominal pain: Mild stomach discomfort is relatively common, especially with higher doses.
• Diarrhea: Usually mild and self-limiting.
• Vomiting: More common with higher doses. If vomiting occurs shortly after taking the dose, contact your pharmacist or provider about retaking it.
• Rash: A mild rash affects a small percentage of patients. However, any rash should be reported to your provider promptly because rarely it can signal a more serious skin reaction.
• Elevated liver enzymes: Detected on blood tests; usually asymptomatic and reversible when fluconazole is stopped. More common with prolonged use or higher doses.

Less Common Side Effects (0.1–1% of Patients)

• Loss of appetite (anorexia)
• Fatigue
• Constipation
• Taste changes (dysgeusia)

Serious Side Effects: When to Call Your Doctor or Seek Emergency Care

While rare, the following side effects are serious and require prompt medical attention:

Liver damage (hepatotoxicity). Signs include yellowing of the skin or whites of the eyes (jaundice), dark-colored urine, pale stools, severe fatigue, and upper right abdominal pain. Call your doctor right away or go to the emergency room if you experience these symptoms.

Severe skin reactions (Stevens-Johnson Syndrome / Toxic Epidermal Necrolysis). These life-threatening reactions involve rapidly spreading, painful rash, blistering, peeling skin, and sores in the mouth and eyes. If you develop any rash while taking fluconazole, stop the medication immediately and contact your provider. Do not wait to see if the rash improves.

Heart rhythm problems (QT prolongation). Fluconazole can prolong the QT interval, which may cause abnormal heart rhythms. Symptoms include palpitations, dizziness, fainting, or an irregular heartbeat. Seek emergency care if you experience these symptoms. Risk is higher when taking other QT-prolonging medications.

Severe allergic reactions (anaphylaxis). Symptoms include swelling of the face, lips, tongue, or throat; difficulty breathing; and hives. Call 911 immediately.

Seizures. Rare, but reported. Seek emergency care immediately.

Who Is at Higher Risk for Side Effects?

Certain groups have a higher risk of fluconazole side effects and require closer monitoring:

• Patients with pre-existing liver disease: Liver toxicity risk is higher. Liver function tests should be monitored.
• Patients with kidney disease: Fluconazole is primarily excreted by the kidneys; dose reduction required for significant renal impairment.
• Patients taking QT-prolonging medications: Including antiarrhythmics, certain antibiotics (erythromycin), pimozide, and quinidine. Some combinations are contraindicated.
• Pregnant women: Fluconazole is associated with increased miscarriage risk and potential birth defects. Avoid use in pregnancy when possible.

Managing Common Side Effects

For the minor GI side effects (nausea, stomach pain, diarrhea):

• Take fluconazole with food or milk if nausea is a problem (food does not significantly affect absorption).
• Stay well hydrated.
• Avoid alcohol while on fluconazole — alcohol increases liver strain and may worsen GI side effects.

Side Effects Are Not a Reason to Stop Without Consulting Your Doctor

If you're experiencing side effects, call your provider before stopping fluconazole — stopping early may allow your infection to return or become resistant. Your provider can help you weigh the benefits and risks and decide the best course of action. For more on drug safety, see our guide on fluconazole drug interactions. And if you need help finding a pharmacy with fluconazole in stock, medfinder.com can help.