Diflucan (Fluconazole): Uses, Dosage & Safety Information

Diflucan is prescription fluconazole, an antifungal taken as a tablet or oral suspension. It is licensed for vaginal, oropharyngeal and oesophageal candidiasis, cryptococcal meningitis, and prevention of candidiasis after bone marrow transplantation. High-dose use through the first trimester has been linked to a distinctive pattern of birth defects.

What makes this drug unusual is the distance between its smallest and largest use. Vaginal thrush is treated with a single 150 mg tablet and nothing else. Cryptococcal meningitis is treated with daily dosing that continues for weeks, often followed by indefinite suppression. Both are fluconazole; almost nothing else about them is the same.

The oral and intravenous doses are identical, because absorption after a tablet is rapid and almost complete. That is why a switch from drip to tablet changes nothing about the dose, and it is also why one tablet can do the work of a course in a shallow infection.

The brand today is tablets in four strengths and a powder for oral suspension. All of the premixed intravenous presentations of Diflucan are recorded as discontinued, so the infusion a hospital hangs is generic fluconazole rather than this brand.

Other azoles used for different targets are covered separately: Vfend for invasive aspergillosis, Sporanox and itraconazole for nail and systemic mycoses, and nystatin, which is not absorbed at all.

For vaginal candidiasis: one 150 mg tablet, once, with or without food. There is no course to complete and no second tablet by default.¹

For everything else: a loading dose of twice the daily dose on the first day, then daily dosing at the same time each day, for as long as the prescriber sets. Improvement in symptoms is not the endpoint in these infections, and stopping early is how a partially treated fungal infection relapses.

Tablets and suspension are interchangeable at the same milligram dose, as is the intravenous route, because absorption by mouth is near complete.

Tell the prescriber about pregnancy or a possible pregnancy before taking any dose, including the single one. This is not routine caution: the fetal risk on this drug is dose-dependent in a way that is documented, and the single-dose exposure is the one most likely to happen without a conversation.

Substances that interact with fluconazole are listed once, in the interactions table below.

The single dose has its own dataset, and it is worth reading separately. Among 448 women treated with one 150 mg tablet for vaginal candidiasis, side effects possibly related to the drug occurred in 26%, against 16% in 422 women given active comparators.¹

That last row is the one that unsettles the neat story. It would be convenient if risk scaled with dose, so that one tablet carried none. The label says the opposite about hepatotoxicity: in the cases associated with this drug, no obvious relationship to total daily dose, duration of therapy, sex or age was found. Rare remains rare, but rare is not zero, and it is not confined to the long courses.

Diflucan is licensed for vaginal candidiasis; oropharyngeal and oesophageal candidiasis; cryptococcal meningitis; and prophylaxis of candidiasis in patients undergoing bone marrow transplantation. The label also records effectiveness in Candida urinary tract infection, peritonitis and systemic candidiasis, but from open non-comparative studies in relatively small numbers of patients — a weaker footing than the numbered indications.¹

What it does not treat is the more useful half of that list. Bacterial vaginosis, bacterial vaginitis and bacterial vulvovaginitis are bacterial, not fungal, and an antifungal does nothing for any of them. Discharge and irritation feel similar enough that a tablet bought on the assumption of thrush is a common way to delay the right treatment by a week.

Candidiasis is what the single dose is for. A first uncomplicated episode is the clean case; recurrent episodes, or symptoms that return within weeks, are a reason for testing rather than a second tablet.

For urinary tract infection the distinction matters just as much: the overwhelming majority are bacterial, and Candida in the urinary tract is a different clinical situation that mostly arises in catheterised or immunocompromised patients.

Cryptococcal meningitis sits at the other end of the page entirely. It is treated in hospital, the label directs prescribers to the clinical studies section before use in AIDS patients, and it is the reason fluconazole exists in 200 mg tablets and in suspension.

Diflucan is prescription-only in the United States in every form, including the single 150 mg tablet.² In some other countries the single dose is sold from a pharmacy without a prescription, which is why advice found online about buying it varies so much by where it was written.

Generic fluconazole is widely listed as tablets, powder for suspension and infusion, so a prescription written for Diflucan is usually filled with the generic at the same strength.⁴

The two things that do not change with the label on the box are set out once each: what pregnancy means for this drug is in Critical warnings for Diflucan use, and which medicines it disturbs is in Drug interactions with Diflucan.

Fetal harm is dose-dependent, and the low dose is not cleared

Case reports describe a distinctive and rare pattern of birth defects in infants whose mothers took 400 to 800 mg a day through most or all of the first trimester: brachycephaly, abnormal facies, abnormal calvarial development, cleft palate, femoral bowing, thin ribs and long bones, arthrogryposis and congenital heart disease. Similar effects were seen in animal studies. Separately, retrospective epidemiological studies have suggested potential risks of spontaneous abortion and congenital abnormality with 150 mg as a single or repeated dose in the first trimester.¹

Liver injury without a dose threshold

Rare cases of serious hepatic toxicity, including fatalities, have been associated with this drug, primarily in patients with serious underlying conditions. In those cases no obvious relationship to total daily dose, duration of therapy, sex or age was found, so a short course is not automatically outside the risk.

QT interval

Coadministration with other drugs that prolong the QT interval and are metabolised by CYP3A4 is contraindicated. The combinations are listed once, in the interactions table below.

Hypersensitivity

Known hypersensitivity to fluconazole or its excipients is a contraindication. The label states there is no information on cross-hypersensitivity with other azoles, and advises caution rather than assuming either safety or danger.

When one tablet is the wrong answer

Recurrent thrush, symptoms that do not settle, or a diagnosis made without examination are all reasons to be assessed rather than to repeat the dose. Bacterial vaginosis and bacterial vaginitis produce overlapping symptoms and do not respond to this drug at all.

Source: ¹

The single dose is not a smaller version of the course. It is a different treatment for a different depth of infection, and it does not scale: two tablets do not treat a deeper infection, and a course is not what an uncomplicated first episode of thrush needs.

Fluconazole inhibits the liver enzymes that clear a long list of common medicines, so the interaction question applies to the single dose as well as to a course — a one-off tablet still raises levels for several days.¹

Source:

This table is the only place on this page where interacting substances are listed. Because the contraindicated list is revised, it is read from the current prescribing information rather than reproduced here in a form that could go stale.

Evidence scope

What has been reported to the FDA

As of the FAERS data cut of 30 July 2026, the FDA Adverse Event Reporting System held 69,682 reports naming fluconazole, 58,994 of them coded serious.³

Who was this medicine studied in?

No FDA Drug Trials Snapshot exists for Diflucan. Snapshots are published only for new molecular entities approved from January 2015 onward, and the tablets were approved on 29 January 1990.

The evidence behind the label is not one population but several, and they barely overlap. The single-dose data come from comparative trials in 448 women with vaginal candidiasis. The cryptococcal meningitis data come from studies in AIDS patients, and the label directs prescribers to read that section before treating them. The systemic candidiasis uses rest on open non-comparative studies in small numbers.

That structure is worth holding onto when reading anything about this drug: a statement about fluconazole is usually a statement about one of those populations, and it rarely transfers to the others.

Who this is and is not appropriate for

Typically considered for: a non-pregnant adult with a first, uncomplicated episode of vaginal candidiasis, for the single dose; and, for the multi-dose courses, a person with oropharyngeal or oesophageal candidiasis, cryptococcal meningitis, or undergoing bone marrow transplantation, under the care of the team treating that condition.

Not appropriate for: anyone with known hypersensitivity to fluconazole or its excipients; anyone taking a QT-prolonging drug metabolised by CYP3A4, which the label contraindicates; and anyone whose symptoms have not been established as fungal, since bacterial vaginosis and bacterial vaginitis look similar and do not respond.

Needs a conversation first: anyone pregnant or who might be, at any dose; anyone with liver dysfunction, since the label directs caution and the hepatotoxicity has no dose threshold; and anyone taking warfarin, phenytoin, a sulfonylurea, ciclosporin or tacrolimus, because one tablet is enough to move their levels for days.¹

Where to go next

• Report a side effect: FDA MedWatch, or MHRA Yellow Card in the UK
• Full prescribing information, including the current contraindicated drug list: DailyMed
• Pregnancy-specific enquiries: MotherToBaby, or Bumps in the UK
• Recurrent or unresolving symptoms: assessment and testing rather than a repeat dose

1. FDA Prescribing Information — DIFLUCAN (fluconazole), Pfizer. Indications and Usage; Dosage and Administration; Contraindications; Warnings, including Hepatic Injury and Potential for Fetal Harm; Adverse Reactions, single-dose vaginal candidiasis experience; Precautions, Pregnancy.
   Label revised 2026-04 · Accessed 2026-08-30
   Used for: licensed indications, single and multiple dose regimens, contraindications, single-dose adverse rates against comparator, hepatotoxicity without dose relationship, first-trimester defect pattern
   DailyMed SPL f694c617-3383-416c-91b6-b94fda371204
2. Drugs@FDA via openFDA — applications recorded under the brand name DIFLUCAN: NDA 019949 tablets 50, 100, 150 and 200 mg, approved 1990-01-29; NDA 020090 powder for oral suspension, approved 1993-12-23; NDA 019950 premixed infusions, all presentations recorded as Discontinued.
   Accessed 2026-08-30
   Used for: approval dates, application numbers, which forms remain marketed under the brand
   Drugs@FDA, products.brand_name DIFLUCAN
3. FDA Adverse Event Reporting System via openFDA, query on fluconazole.
   Data cut 2026-07-30 · Accessed 2026-08-30
   Used for: report counts, serious-coded share, most frequently coded reaction terms
   openFDA FAERS
4. FDA National Drug Code Directory via openFDA, query on fluconazole.
   Accessed 2026-08-30
   Used for: which presentations are currently listed and their marketing categories
   openFDA NDC Directory

This page is medical information, not medical advice. It describes a prescription medicine used at doses ranging from one tablet to months of daily treatment, and does not replace assessment by a clinician who knows your history, your other medicines and whether you might be pregnant.