Nystatin

What it is

Nystatin is a polyene macrolide antifungal obtained from the soil bacterium Streptomyces noursei. It is a mixture rather than a single pure compound, and its main component, nystatin A, is closely related to amphotericin B. Taken by mouth it is essentially a local treatment: it is absorbed very sparingly, with no detectable blood levels at recommended doses. It is supplied as an oral suspension, as pastilles or lozenges in some countries, as oral tablets for the gut, and as creams, ointments and powders for the skin.

What the research says

Nystatin kills Candida on contact with the surfaces it touches, and its evidence is correspondingly local and uneven. A systematic review found nystatin pastilles clearly better than placebo for denture-associated candidiasis, but nystatin suspension no better than fluconazole in infants, children or people with HIV, and a small randomised trial in infants with thrush found clinical cure in 32 percent on nystatin suspension versus 100 percent on fluconazole. For preventing invasive fungal infection in very low birth weight babies the randomised evidence looks strong in relative terms but the trials are methodologically weak and no mortality benefit was shown. It was once prescribed long-term for a supposed systemic candida hypersensitivity syndrome; a randomised trial in 1990 showed no effect on systemic symptoms beyond placebo. Its harms are mostly gastrointestinal and tolerability-related, with occasional hypersensitivity reactions.

Evidence grade: Limited evidence.

How it works

Drug class: Polyene macrolide antifungal (non-absorbed, topical and oral)

Nystatin binds to sterols, chiefly ergosterol, in the fungal cell membrane. The bound molecules make the membrane leaky, so the contents of the fungal cell escape and the cell dies. Human cells use cholesterol rather than ergosterol, which is why a drug this destructive to fungi can be put in the mouth. Because almost none of it crosses the gut wall, it acts only where it physically touches fungus and is useless against fungal infection in the bloodstream or organs. (Source 1)

What it is used for

• A systematic review found nystatin pastilles significantly better than placebo for denture stomatitis, and, in the review's descriptive non-pooled comparisons only, higher cure rates at 400,000 IU than 200,000 IU and better results over 4 weeks than 2 weeks. The suspension is the weaker formulation: it was not superior to fluconazole in infants, children or HIV/AIDS patients, and in a small randomised trial in infants it cured 32 percent against fluconazole's 100 percent. Evidence: limited. (Source 2)
• Meta-analyses find large relative reductions in fungal colonisation and invasive fungal infection, but the Cochrane review stresses quasi-randomisation, absent allocation concealment and unblinded assessment in the included trials, and no analysis has shown a mortality benefit. A head-to-head randomised trial found oral nystatin and intravenous fluconazole similarly effective. Evidence: limited. (Source 3)
• The Cochrane review of prophylaxis found the benefit confined to antifungals that are absorbed or partially absorbed from the gut. Nystatin is not absorbed, so the review's finding does not support using it for this purpose. Evidence: not-supported. (Source 4)
• A 2026 systematic review of four observational studies and one randomised trial in 2,060 patients found a numerically lower rate of fungal peritonitis with nystatin given alongside antibiotics, but the pooled estimate for the primary analysis was not statistically significant and rested on unadjusted data. Evidence: limited. (Source 5)
• A 32-week randomised double-blind crossover trial in 42 women found nystatin no better than placebo for systemic or psychological symptoms, with a 2 percentage point difference in symptom improvement, and concluded that long-term nystatin for this purpose is unwarranted. Evidence: not-supported. (Source 6)
• Oral nystatin cannot do this. It is absorbed very sparingly, with no detectable blood levels at recommended doses, and the label states plainly that it is not effective in systemic mycoses. Evidence: not-supported. (Source 1)

Interactions

• Other medicines taken by mouth or by injection (systemic drug interactions) (label): Pharmacokinetic interactions are not expected from swallowed nystatin because essentially none of it reaches the bloodstream: no blood levels are detectable at recommended doses. The flip side is that it cannot treat anything beyond the surfaces it touches. (Source 1)
• Probiotic yeasts such as Saccharomyces boulardii (theoretical): Nystatin kills yeasts by binding sterols in their membranes, and Saccharomyces boulardii is a yeast, so an antifungal taken into the same mouth and gut would be expected to reduce a live yeast probiotic's viability. This is reasoning from the mechanism: we found no clinical study of the pair, so treat it as theoretical rather than demonstrated. (Source 1)
• Eating and drinking soon after a dose (label): Because the suspension works by contact, washing it away matters. The label's instruction is to hold it in the mouth as long as possible before swallowing and to keep going for at least 2 days after symptoms settle, which implies that food and drink straight after a dose shorten the contact time. (Source 1)
• Sucrose content of the oral suspension (label): The cherry-flavoured suspension contains sucrose as an inactive ingredient. That is worth knowing for anyone counting sugar, and it is held in the mouth repeatedly through the day, which is the pattern that matters for teeth. Nothing in the label quantifies the amount or links it to a measured outcome. (Source 7)
• Alcohol (label): No alcohol interaction is documented. The label has no drug interactions section at all, and because swallowed nystatin does not reach the bloodstream there is no systemic route for one; our searches found no human study of nystatin with alcohol. An alcohol-containing mouthwash used at the same time would be a contact-time question rather than a pharmacological interaction. (Source 1)

Stopping it

• There is no withdrawal syndrome and no taper; the issue with nystatin is stopping too early. The label's position is that treatment should carry on for at least 48 hours after perioral symptoms have gone or cultures have returned to normal, and that the course should not be interrupted even if symptoms settle within a few days. (Source 8)
• The same label section records that the course should not be interrupted or discontinued before it is finished even though relief may come within days, which is the practical reason for relapse. (Source 1)
• Duration appears to matter to the result, not just to relapse: the systematic review found 4 weeks of nystatin pastilles seemed to work better than 2 weeks, so stopping at two weeks may be stopping short. (Source 2)
• One reason relapse after stopping is common with the suspension is that it is the weaker form. The review of the trial literature notes there is no universally accepted dose, formulation or duration, which is itself a statement about how thin the stopping evidence is. (Source 9)

What goes wrong

In a systematic review of 24 nystatin trials, only six reported adverse effects at all, and nausea, vomiting, unpleasant taste and diarrhoea occurred in both nystatin and control groups. (Source 10)

• Systematic review, Very low certainty.
• Size: 24 trials reviewed, 6 reporting adverse effects.
• Who: people with oral candidiasis including denture wearers, infants and children, and people with HIV or AIDS.
• How long: treatment courses from 7 to 21 days.
• Result: Bakhshi 2012 (denture): nausea in 6, vomiting in 1, diarrhoea in 5, anorexia in 1, burning in 1 on nystatin, versus itching in 1 control. Nairn 1975: unpleasant taste in 8 nystatin versus 5 control. Flynn 1995 (infants and children): 3 patients with vomiting, nausea, diarrhoea, anorexia and abdominal pain on nystatin versus 6 in the control group.
• Funding: not stated; the review notes 18 of 24 trials did not report adverse effects as a secondary outcome at all, so these counts understate what is unknown.

Limit of this finding: These are raw counts from individual trials, not pooled rates, so they cannot be turned into a frequency. Eighteen of the twenty-four trials did not report adverse effects at all, which means the real question is how much was never measured rather than how little was found.

Six trials [ 31 , 37 , 43 , 45 , 49 , 50 ] out of twenty-four reported adverse effects after the administration of nystatin, while the remaining eighteen trials did not mention any adverse effects as secondary outcomes.

The regulator's position records gastrointestinal symptoms and hypersensitivity reactions including anaphylactoid reaction with nystatin oral suspension, without frequencies. (Source 8)

• Official position, Very low certainty.
• Size: not stated; spontaneous and trial reports summarised by the regulator.
• Who: users of nystatin oral suspension.
• How long: not stated.
• Result: No rates are given. Reported events are diarrhoea, gastrointestinal distress, nausea, vomiting, burning of the mouth, rash, pruritus and anaphylactoid reaction. Doses above five million units daily have caused nausea and gastrointestinal upset.
• Funding: manufacturer label as summarised by the US National Library of Medicine, revised March 2026.

Gastrointestinal symptoms including diarrhea, gastrointestinal distress, nausea, vomiting and burning of the mouth have been reported. Hypersensitivity reactions including rash, pruritus, and anaphylactoid reaction have also been reported.

What the evidence supports

In three randomised trials pooled for denture-associated candidiasis, conventional nystatin therapy performed at least as well as antimicrobial photodynamic therapy, on low-certainty evidence. (Source 11)

• Meta-analysis, Low certainty.
• Size: 3 randomised controlled trials, 141 participants.
• Who: patients with Candida-associated denture stomatitis.
• How long: searches to 15 August 2021.
• Result: Pooled results favoured nystatin therapy over photodynamic therapy for reducing Candida colony count (log10 CFU/mL) on palate and denture; moderate risk of bias and low certainty by GRADE.
• Funding: not stated in the abstract.

Based on the pooled results, NYT compared to aPDT generally performed better in reducing Candida colony count (Log10 CFU/mL) in patients' palate and patients' denture.

What the evidence does not support

In a randomised trial in 34 infants with oral thrush, nystatin suspension cured 32 percent against fluconazole's 100 percent. (Source 12)

• Randomized trial, Low certainty.
• Size: 34 infants randomised (19 nystatin, 15 fluconazole)
• Who: otherwise healthy young infants with oral candidiasis.
• How long: nystatin four times daily for 10 days versus fluconazole once daily for 7 days.
• Result: Clinical cure 6 of 19 (32%) with nystatin versus 15 of 15 (100%) with fluconazole, P < 0.0001.
• Funding: not stated; described by its own authors as a small pilot study.

Clinical cures for nystatin were 6 of 19 (32%), and those for fluconazole were 15 of 15 (100%), P < 0.0001.

A 32-week randomised double-blind crossover trial found nystatin no better than placebo for the systemic symptoms attributed to candidiasis hypersensitivity syndrome. (Source 6)

• Randomized trial, Low certainty.
• Size: 42 premenopausal women.
• Who: women meeting the criteria for candidiasis hypersensitivity syndrome with a history of candida vaginitis.
• How long: 32 weeks, four crossover combinations of oral and vaginal nystatin or placebo.
• Result: Systemic symptom scores improved 25 percent on the active regimens and 23 percent on all-placebo, a difference of 2 percent (95% CI -3 to 7 percent); vaginal symptoms did improve more on nystatin.
• Funding: not stated in the abstract.

Limit of this finding: This trial tested long-term nystatin for candidiasis hypersensitivity syndrome, a contested diagnosis in which general symptoms are attributed to candida. It enrolled 42 premenopausal women in a 32-week crossover design. It is not evidence about treating thrush or any confirmed candida infection, and with 42 participants a null result cannot rule out a small effect.

On average, the scores for systemic symptoms improved 25 percent with the three active-treatment regimens and 23 percent with the all-placebo regimen, a difference of only 2 percent (95 percent confidence interval, -3 to 7 percent).

A longitudinal mother-child cohort found that clinically used oral nystatin did not reduce Candida albicans carriage in children, and identified nystatin-resistant isolates. (Source 13)

• Cohort study, Very low certainty.
• Size: 41 mothers and their children, 126 Candida isolates.
• Who: mother-infant pairs followed from birth to 2 years.
• How long: 0 to 2 years.
• Result: Caspofungin was most active against oral Candida, then fluconazole, then nystatin; two missense mutations in the CDR2 gene were shared among nystatin-resistant C. albicans isolates; 70 percent of children's isolates stayed stable on antifungals over 2 years.
• Funding: not stated in the abstract; small cohort, with susceptibility measured in vitro rather than clinical cure.

Results of the longitudinal cohort indicated that clinically used oral nystatin was ineffective in reducing the carriage of C. albicans in children; novel antifungal regimens in infants are needed for better oral yeast control.

A Cochrane review of prophylaxis in cancer chemotherapy found benefit only for antifungals absorbed or partially absorbed from the gut, which excludes nystatin. (Source 4)

• Systematic review, Low certainty.
• Size: 15 studies with 1,164 randomised patients for the oral candidiasis outcome.
• Who: people with cancer (excluding head and neck cancer) receiving chemotherapy.
• How long: chemotherapy courses; searches to July 1999.
• Result: Partially absorbed agents risk ratio 0.13 (95% CI 0.06 to 0.27), number needed to treat 3 (95% CI 3 to 5); the benefit was attributed to absorption, and the review concluded the absorbed and partially absorbed agents were the effective ones.
• Funding: not stated in the abstract; the review notes that general reporting of the randomised trials was poor.

There is evidence that prophylactic use of antifungal agents which are absorbed or partially absorbed from the gastrointestinal tract reduce the clinical signs of oral candidiasis

Where the evidence is mixed

A systematic review and meta-analysis found nystatin pastilles significantly better than placebo for denture stomatitis, while nystatin suspension was not better than fluconazole for oral candidiasis. (Source 2)

• Systematic review, Low certainty.
• Size: randomised controlled trials in four databases to 1 July 2015.
• Who: people with oral candidiasis, including denture stomatitis, infants, children and people with HIV/AIDS.
• How long: treatment courses of 2 to 4 weeks.
• Result: Pastille superior to placebo in denture stomatitis; suspension not superior to fluconazole; 400,000 IU pastilles gave a significantly higher mycological cure rate than 200,000 IU; 4 weeks appeared better than 2 weeks.
• Funding: not stated in the abstract; the review's own conclusion calls for more well designed high quality randomised studies.

Limit of this finding: Only two of these comparisons come from the pooled meta-analysis: pastilles against placebo in denture stomatitis, and suspension against fluconazole. The dose comparison (400,000 IU against 200,000 IU), the four-weeks-against-two-weeks comparison and the pastille-against-suspension comparison are what the review itself calls descriptive investigations and indirect evidence, so they are not pooled trial results and should not be read as firm.

The meta-analysis showed that nystatin pastille was significantly superior to placebo in treating denture stomatitis. Nystatin suspension was not superior to fluconazole in treating oral candidiasis in infants, children, or HIV/AIDS patients.

A Cochrane review of non-absorbed antifungal prophylaxis, pooling nystatin and miconazole trials together, found a large reduction in invasive fungal infection in very low birth weight infants but no mortality benefit, on trials it judged methodologically weak. (Source 3)

• Systematic review, Low certainty.
• Size: 4 trials, 1,800 infants, versus placebo or no drug; plus 3 trials, 326 infants, versus systemic antifungals.
• Who: very preterm or very low birth weight infants.
• How long: neonatal unit stay; no trial assessed post-discharge outcomes.
• Result: Invasive fungal infection typical risk ratio 0.20 (95% CI 0.14 to 0.27), risk difference -0.18 (-0.21 to -0.15), with substantial heterogeneity; mortality typical risk ratio 0.87 (0.72 to 1.05), risk difference -0.03 (-0.06 to 0.01)
• Funding: not stated in the abstract; the review lists quasi-randomisation, lack of allocation concealment and lack of blinding, and notes very high control-group infection rates in three of the four trials.

Limit of this finding: The fivefold reduction in invasive fungal infection (risk ratio 0.20) is not a nystatin-specific number. This Cochrane review pooled trials of nystatin together with trials of miconazole under one heading, oral/topical non-absorbed antifungal prophylaxis, so the figure describes the two drugs combined and cannot be read as nystatin's own effect. The review also found no reduction in deaths and judged the underlying trials methodologically weak.

These trials had various methodological weaknesses including quasi-randomisation, lack of allocation concealment, and lack of blinding of intervention and outcomes assessment.

A 2022 meta-analysis of five randomised trials found oral nystatin prophylaxis reduced fungal colonisation and invasive fungal infection in very low birth weight infants but did not reduce mortality or length of stay. (Source 14)

• Meta-analysis, Low certainty.
• Size: 5 randomised controlled trials (4 contributing to most outcomes)
• Who: very low birth weight infants in neonatal intensive care.
• How long: databases searched from inception to June 2022; outcomes over the NICU stay.
• Result: Fungal colonisation RR 0.34 (95% CI 0.24-0.48, p<0.0001); invasive fungal infection RR 0.15 (0.12-0.19, p<0.0001); antibiotic duration -2.79 days (-5.01 to -0.56); mortality RR 0.87 (0.64-1.18, p=0.37); NICU stay -2.85 days (-6.52 to 0.82, p=0.13)
• Funding: not stated in the abstract; one included trial rated high risk of bias and one with some concerns.

Limit of this finding: Every estimate here comes from a fixed-effect pooling of five small randomised trials, one rated at high risk of bias and one with some concerns. Fixed-effect pooling assumes all the trials are measuring the same underlying effect, which makes the confidence intervals look tighter than this small and uneven evidence base justifies.

However, there was no significant difference between both groups regarding the rate of mortality (n=4 RCTs, RR=0.87, 95% CI {0.64, 1.18}, p=0.37)

A 2026 systematic review found oral nystatin given with antibiotics did not significantly reduce antibiotic-related fungal peritonitis in peritoneal dialysis in its primary analysis. (Source 5)

• Systematic review, Very low certainty.
• Size: 5 studies (4 prospective observational, 1 randomised), 2,060 peritoneal dialysis patients.
• Who: adults on peritoneal dialysis receiving systemic antibiotics.
• How long: searches to 1 October 2025.
• Result: 13 events in 1,044 peritonitis episodes with nystatin versus 31 in 1,016 controls, OR 0.53 (95% CI 0.18-1.57); in the two studies reporting prescription-level data, 7/2,205 versus 16/1,724, OR 0.35 (0.15-0.87)
• Funding: not stated in the abstract; the review states all pooled estimates used unadjusted data with few events, precluding causal inference.

Limit of this finding: The only statistically significant estimate in this review is the prescription-level analysis, which comes from two of the five studies. The main episode-level estimate includes the possibility of no effect at all (odds ratio 0.53, 95% confidence interval 0.18 to 1.57). Four of the five studies were observational, and the review states its pooled estimates rest on unadjusted data with few events, so this is not evidence that nystatin prevents fungal peritonitis.

ARFP yielded 13 events among 1044 peritonitis episodes in the nystatin-treated patients versus 31 among 1016 in the control group (OR 0.53; 95% CI, 0.18-1.57).

A randomised trial comparing intravenous fluconazole with oral nystatin prophylaxis in very low birth weight infants found similar efficacy, with more retinopathy of prematurity treated in the nystatin group. (Source 15)

• Randomized trial, Low certainty.
• Size: 120 neonates under 32 weeks gestation and under 1500 g, 60 per group.
• Who: very low birth weight infants in a neonatal unit.
• How long: from the first 72 hours of life through the hospital stay.
• Result: Systemic fungal infection in 6 of 120 (5.0%), three in each group; 3 deaths (2.5%), two in the nystatin group; retinopathy of prematurity treated in 4 of 60 (6.7%) nystatin versus 1 of 60 (1.7%) fluconazole, p = 0.040; intraventricular haemorrhage in 3 (5.0%) nystatin versus 7 (11.7%) fluconazole, p = 0.020.
• Funding: not stated in the abstract; very few events, so the secondary differences are fragile and the authors ask for larger studies before routine use.

Limit of this finding: The trial labels its arms by letter, and the letters are defined in its methods: group A received intravenous fluconazole and group B received oral nystatin. So the extra retinopathy of prematurity treatment was in the nystatin arm and the extra intraventricular haemorrhage in the fluconazole arm. Both rest on three or four events in 60 infants per arm, which is far too few to establish either as a drug effect; the authors ask for larger studies.

Four (6.7%) patients in group B and one (1.7%) in group A were treated for retinopathy of prematurity (p = 0.040).

Where the research disagrees

Whether nystatin is an adequate first treatment for oral candidiasis, or a weaker option kept for habit and cost

• US label for nystatin oral suspension (March 2026), position, stating the approved indication without comparative data: Nystatin oral suspension is indicated for the treatment of infections of the oral cavity caused by Candida albicans . (Source 1)
• Lyu and colleagues, Drug Design, Development and Therapy 2016, systematic review and meta-analysis of randomised trials: Nystatin pastille was significantly superior to placebo in treating denture stomatitis, while nystatin suspension was not superior to fluconazole in treating oral candidiasis in infants, children, or HIV/AIDS patients. (Source 2)
• Goins and colleagues, Pediatric Infectious Disease Journal 2002, small randomised trial, 34 infants: In this small pilot study fluconazole was shown to be superior to nystatin suspension for the treatment of oral thrush in otherwise healthy infants. (Source 12)

Whether nystatin prophylaxis should be used routinely in very low birth weight infants

• Cochrane Neonatal review, 2015, systematic review of four trials in 1,800 infants with quasi-randomisation and unblinded assessment: The finding of a reduction in risk of invasive fungal infection in very low birth weight infants treated with oral/topical non-absorbed antifungal prophylaxis should be interpreted cautiously because of methodological weaknesses in the included trials. (Source 3)
• Cureus meta-analysis, 2022, meta-analysis of five randomised trials, three rated low risk of bias: Compared with the control group, oral nystatin prophylaxis was correlated with substantial decrease in the frequency of fungal colonization (n=4 RCTs, RR=0.34, 95% CI {0.24, 0.48}, p<0.0001) (Source 14)

How much

• Reference intake: There is no dietary reference intake for nystatin: it is a prescription antifungal and the dose is set by the prescriber. As a position dated March 2026, the US label for the oral suspension states 2 mL (200,000 units) four times daily for infants and 4 to 6 mL (400,000 to 600,000 units) four times daily for children and adults, held in the mouth as long as possible. (Source 16)
• Upper limit: No upper intake level exists in the nutrition sense. The nearest statement is the label's overdosage note, a position dated March 2026: oral doses above five million units daily have caused nausea and gastrointestinal upset. Because almost none is absorbed, systemic toxicity from swallowed nystatin is not the limiting factor. (Source 8)
• Studied: In the review's descriptive, non-pooled comparisons, nystatin pastilles at 400,000 IU gave a significantly higher mycological cure rate than 200,000 IU, and 4 weeks of pastilles appeared better than 2 weeks. (Source 2)
• Studied: A review of the trial literature records that nystatin is usually given at 200,000 to 400,000 IU four times a day, and 100,000 to 200,000 IU in infants and neonates, for about 4 weeks, but that no dosage, formulation or duration is universally accepted. (Source 9)
• Studied: The infant thrush trial gave nystatin oral suspension four times a day for 10 days against fluconazole 3 mg/kg once daily for 7 days. (Source 12)
• Studied: The neonatal prophylaxis trial gave oral nystatin 1 mL (100,000 units) every eight hours against intravenous fluconazole 3 mg/kg twice weekly. (Source 15)

A common belief, and what the research shows

The belief: Candida overgrowth in the gut causes fatigue, brain fog, premenstrual symptoms and low mood, and a long course of nystatin clears it.

What the research shows: That idea was tested directly. In a 32-week randomised double-blind crossover trial in 42 women who met the criteria for candidiasis hypersensitivity syndrome, nystatin by mouth, by vagina, both, or neither all improved symptoms, and the drug added almost nothing: "the scores for systemic symptoms improved 25 percent with the three active-treatment regimens and 23 percent with the all-placebo regimen, a difference of only 2 percent (95 percent confidence interval, -3 to 7 percent)." The authors concluded that "the empirical recommendation of long-term nystatin therapy for such women appears to be unwarranted." There is also a pharmacological reason the idea cannot work the way it is told: nystatin is not absorbed, so it cannot act on anything beyond the surfaces it touches, and the label states it "is not effective in the treatment of systemic mycoses since it is not significantly absorbed from the gastrointestinal tract."

Questions and answers

What is it?

Nystatin is an antifungal substance made by the soil bacterium Streptomyces noursei, not a nutrient or a part of the human body. It is a polyene macrolide, chemically close to amphotericin B, and it is a mixture rather than a single pure compound. It is the antifungal dentists prescribe most often, and it comes as an oral suspension, as pastilles, as tablets and as skin creams, ointments and powders. (Source 9)

What does it do in the body?

It binds to sterols in the fungal cell membrane and makes it leaky, so the cell's contents spill out and the fungus dies. Human cells use cholesterol instead of ergosterol, which is why the same molecule is tolerated in the mouth. Because almost none of it is absorbed, it only works where it physically touches the fungus, and it does nothing for fungal infection in the blood or organs. (Source 1)

Is it good or bad for you?

It is useful for the specific job of clearing Candida off a surface, and useless or misleading beyond that. The pastille form beat placebo for denture-associated candidiasis, and in very low birth weight infants prophylaxis reduced invasive fungal infection in relative terms, though without a mortality benefit and on weak trials. The suspension was no better than fluconazole in infants, children or people with HIV, and in one small trial clearly worse in infants. Taken long-term for a supposed systemic candida syndrome it did nothing beyond placebo. (Source 2)

How do you get more of it?

There is no dietary or behavioural route: nystatin is a manufactured prescription medicine, available as a suspension, pastilles, tablets and topical preparations, and the dose and course are set by the prescriber. What the evidence says about getting more of it to work concerns formulation and contact, and it is indirect: in the review's descriptive, non-pooled comparisons pastilles did better than suspension, higher-strength pastilles better than lower, and longer courses better than shorter ones. (Source 2)

If it is harmful, what reduces it?

It leaves the body on its own: almost none is absorbed and what is swallowed passes through the gut. If a reaction occurs the label's instruction is to stop it rather than reduce it, and it is contraindicated in anyone with a history of hypersensitivity to nystatin or to the suspension's other ingredients. (Source 1)

Why might someone be low in it or missing it?

Does not apply. The body does not make nystatin and nobody can be deficient in it. The nearest real question is why it fails to work in someone taking it, and the literature points to three answers: the suspension is the weaker formulation, courses are often too short, and Candida isolates resistant to nystatin exist, with resistant Candida albicans in one cohort sharing two missense mutations in the CDR2 gene. (Source 13)

Which whole foods contain it or feed it?

No whole food contains nystatin and no food feeds it; it comes from a bacterium cultured industrially, not from the diet. Two food-adjacent facts from the label are worth knowing: the oral suspension contains sucrose among its inactive ingredients, and because the drug works by contact, eating or drinking straight after a dose shortens the time it stays on the affected surface. (Source 7)

What happens if you do not have it?

Not taking nystatin does not create a deficiency; it means a Candida infection is either left alone or treated with something else, and the alternatives are often better. In infants with thrush, 100 percent were cured with fluconazole against 32 percent with nystatin suspension. In very low birth weight infants, untreated control groups in the prophylaxis trials had very high invasive fungal infection rates, which is why the relative reductions looked so large even though mortality did not change. (Source 3)

How can you test for it?

You do not test for nystatin; you test for the fungus it is aimed at. The label's instruction when there is no response is to repeat microbiological studies such as potassium hydroxide smears or cultures, to confirm candidiasis and rule out other organisms before starting another course. Laboratory susceptibility testing of the isolate, reported as a minimum inhibitory concentration, can show whether that strain is nystatin-resistant, but that is a research and reference-laboratory measure and its correlation with clinical cure in the mouth has not been established. (Source 1)

References

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2. Drug design, development and therapy. Efficacy of nystatin for the treatment of oral candidiasis: a systematic review and meta-analysis.. 2016. PMID 27042008, DOI 10.2147/dddt.s100795. Read the source
3. The Cochrane database of systematic reviews. Prophylactic oral/topical non-absorbed antifungal agents to prevent invasive fungal infection in very low birth weight infants.. 2015. PMID 26497202, DOI 10.1002/14651858.cd003478.pub5. Read the source
4. The Cochrane database of systematic reviews. Prevention of oral mucositis or oral candidiasis for patients with cancer receiving chemotherapy (excluding head and neck cancer).. 2000. PMID 10796567, DOI 10.1002/14651858.cd000978. Read the source
5. JAC-antimicrobial resistance. Oral nystatin for the prevention of antibiotic-related fungal peritonitis in peritoneal dialysis patients: a systematic review and meta-analysis of randomized and observational studies.. 2026. PMID 41640628, DOI 10.1093/jacamr/dlag006. Read the source
6. The New England journal of medicine. A randomized, double-blind trial of nystatin therapy for the candidiasis hypersensitivity syndrome.. 1990. PMID 2247104, DOI 10.1056/nejm199012203232501. Read the source
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8. Chartwell RX, LLC, via DailyMed (US National Library of Medicine). Nystatin Oral Suspension, USP - US prescribing information, Adverse Reactions, Overdosage and Dosage. 2026. Read the source
9. Life (Basel). Nystatin Effectiveness in Oral Candidiasis Treatment: A Systematic Review & Meta-Analysis of Clinical Trials (full text, Introduction). 2022. PMID 36362833, DOI 10.3390/life12111677. Read the source
10. Life (Basel). Nystatin Effectiveness in Oral Candidiasis Treatment: A Systematic Review & Meta-Analysis of Clinical Trials (full text, adverse effects). 2022. PMID 36362833, DOI 10.3390/life12111677. Read the source
11. Evidence-based dentistry. Efficacy of antimicrobial photodynamic therapy compared to nystatin therapy in reducing Candida colony count in patients with Candida-associated denture stomatitis: a systematic review and meta-analysis.. 2021. PMID 34862461, DOI 10.1038/s41432-021-0208-9. Read the source
12. The Pediatric infectious disease journal. Comparison of fluconazole and nystatin oral suspensions for treatment of oral candidiasis in infants.. 2002. PMID 12506950, DOI 10.1097/00006454-200212000-00017. Read the source
13. Journal of fungi (Basel, Switzerland). Antifungal Susceptibility of Oral Candida Isolates from Mother-Infant Dyads to Nystatin, Fluconazole, and Caspofungin.. 2023. PMID 37233291, DOI 10.3390/jof9050580. Read the source
14. Cureus. Oral Nystatin Prophylaxis for the Prevention of Fungal Colonization in Very Low Birth Weight Infants: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.. 2022. PMID 36168346, DOI 10.7759/cureus.28345. Read the source
15. Oman medical journal. Comparing Fluconazole and Nystatin as Antifungal Prophylactics in Very Low Birth Weight Infants: A Randomized Clinical Trial.. 2024. PMID 39917040, DOI 10.5001/omj.2024.90. Read the source
16. Chartwell RX, LLC, via DailyMed (US National Library of Medicine). Nystatin Oral Suspension, USP - US prescribing information, Dosage and Administration. 2026. Read the source