Drug & supplement interaction

Saccharomyces Boulardii + Acyclovir

Acyclovir brand names: Zovirax, Zovirax Injection, Sitavig, Avaclyr.

No Known Interaction

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS · Updated July 2026 · Pair last verified Sep 13, 2026

The bottom line No known interaction

We found no known interaction between Saccharomyces Boulardii and Acyclovir in our sources. Absence of a documented interaction is not the same as proven safety, and does not guarantee one does not exist. Do not start, stop, or change a medication or supplement based on this page; confirm with your pharmacist or doctor first. Additionally, although there is no interaction, the two are separately associated with some of the same side effects, which would make a new symptom harder to attribute to one or the other.

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Interaction report

Saccharomyces Boulardii and Acyclovir

We checked these two against our interaction database. Here is what we found.

No Known Interaction Found

We did not find a documented interaction between Acyclovir and Saccharomyces Boulardii in our sources. This does not guarantee that the combination is completely free of risk — there is often limited research on supplements and herbal products, especially around drug interactions.

If you decide to take both, the practical routine is simple: add one new thing at a time and note the date you started it. If the combination is going to disagree with you, it usually shows in the first days to a couple of weeks — and a start date turns “I’ve been feeling off” into something a pharmacist can actually work with. Do not stop a prescribed medicine on your own.

Always talk with your pharmacist or doctor before making changes to your medications or supplements, particularly if you take several medications or have an ongoing health condition.

Saccharomyces Boulardii safety at a glance

Saccharomyces Boul... overall Use caution Generally safe for healthy adults but should be avoided by people who are critically ill or immunocompromised.

Pregnancy Use caution Not enough reliable safety data; speak with your doctor before use.

Breastfeeding Use caution Limited safety information is available, so use only with medical advice.

Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Acyclovir and Saccharomyces Boulardii? Ask Dr. Brian Staiger, PharmD, BCPS directly ›

How we checked

Why No Interaction Is Listed for Acyclovir

Interactions in our licensed database are recorded against drug classes, not just single drug names. Acyclovir is filed under 6 classifications — including organic anion transporter 1 (oat1) substrates, topical drugs, nephrotoxic drugs. Saccharomyces Boulardii has documented interactions with 1 drug class — the most serious being antifungals (minor) — and none of Acyclovir’s classifications are among them.

Classification data comes from our licensed Natural Medicines dataset. A medication can belong to classes beyond those recorded there, so this describes how the check was run — it is not a safety guarantee.

Keep it in perspective

Saccharomyces Boulardii Does Interact With Other Medications

Saccharomyces Boulardii has 40 minor known drug interactions in our database — Acyclovir isn’t one of them. If you take anything else, check it against the full list below.

Minor 40 No known interaction 2,790 (incl. Acyclovir)

Taking anything else?

Check Another of Your Medications Against Saccharomyces Boulardii

Covers the 2,830 medications we’ve checked against Saccharomyces Boulardii. Pick one to open its full report.

What to actually watch for

No Interaction Found — But Data Suggests Saccharomyces Boulardii and Acyclovir May Share Several of the Same Side Effects

This is not an interaction. Neither one changes how your body handles the other, and nothing here says they react together. What our sources do show is that each has separately been linked to the effects below — so taking both can make those effects more likely to turn up, and harder to pin on one or the other if they do. One of them is worth acting on rather than waiting out — marked below.

A higher chance of infection Worth acting on reported in 5.0% of FDA reports for Acyclovir Additional detail
Saccharomyces Boulardii
“Rarely, oral use of Saccharomyces boulardii has been associated with fungemia in both immunocompromised and immunocompetent patients. Numerous cases of Saccharomyces fungemia have been reported in critically ill intensive care unit (ICU) patients, particularly those with indwelling or central venous catheters, those receiving enteral feeding, or those receiving broad-spectrum antibiotics.”

Saccharomyces Boulardii · Natural Medicines adverse-effect record, reported in crohn disease.
6 sources cited

1247. Niault M, Thomas F, Prost J, et al. Fungemia due to Saccharomyces species in a patient treated with enteral Saccharomyces boulardii. Clin Infect Dis 1999;28:930.

4357. Pletinex M, Legein J, Vandenplas Y. Fungemia with Saccharomyces boulardii in a 1-year-old girl with protracted diarrhea. J Pediatr Gastroenterol Nutr 1995;21:113-5. DOI

4358. Fredenucci I, Chomarat M, Boucaud C, et al. Saccharomyces boulardii fungemia in a patient receiving ultra-levure therapy. Clin Infect Dis 1998;27:222-3.

4360. Elmer GW, McFarland LV, Surawicz CM, et al. Behaviour of Saccharomyces boulardii in recurrent Clostridium difficile disease patients. Aliment Pharmacol Ther 1999;13:1663-8.

7329. Cesaro S, Chinello P, Rossi L, Zanesco L. Saccharomyces cerevisiae fungemia in a neutropenic patient treated with Saccharomyces boulardii. Support Care Cancer 2000;8:504-5. PubMed

14459. Munoz P, Bouza E, Cuenca-Estrella M, et al. Saccharomyces cerevisiae fungemia: an emerging infectious disease. Clin Infect Dis 2005;40:1625-34. PubMed
Acyclovir

Listed in the ADVERSE REACTIONS section of the FDA label for Acyclovir, and in voluntary FDA adverse-event reports. Read the label on DailyMed ›
Stomach pain / Nausea / Vomiting reported in 4.9% of FDA reports for Acyclovir Additional detail
Saccharomyces Boulardii
“Rarely, oral use of Saccharomyces boulardii has caused gastrointestinal complaints, such as abdominal cramps, flatulence, nausea, vomiting, and decreased appetite.”

Saccharomyces Boulardii · Natural Medicines adverse-effect record, reported in flatulence.
2 sources cited

98731. Flatley EA, Wilde AM, Nailor MD. Saccharomyces boulardii for the prevention of hospital onset Clostridium difficile infection. J Gastrointestin Liver Dis. 2015;24(1):21-4. PubMed

107608. Awoyemi A, Mayerhofer C, Felix AS, et al. Rifaximin or Saccharomyces boulardii in heart failure with reduced ejection fraction: Results from the randomized GutHeart trial. EBioMedicine 2021;70:103511. PubMed
Acyclovir

Listed in the ADVERSE REACTIONS section of the FDA label for Acyclovir, and in voluntary FDA adverse-event reports. Read the label on DailyMed ›

Reported for Saccharomyces Boulardii but not commonly for Acyclovir: reduced appetite, bloating or gas and diarrhea.

Effects for Acyclovir come from the ADVERSE REACTIONS section of its FDA label; effects for Saccharomyces Boulardii come from the Natural Medicines adverse-effect record, quoted above. Where a percentage is shown, it is the share of 114,761 voluntary FDA FAERS reports for Acyclovir that mention that effect — a reporting proportion, not an incidence rate and not evidence the drug caused it. Wording is matched across sources by our own clinical vocabulary, so treat this as a prompt to pay attention, not a diagnosis.

From our Q&A

Questions About Saccharomyces Boulardii or Acyclovir

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Saccharomyces Boulardii or Acyclovir, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Alternatives To Valtrex For The Treatment Of Herpes Answered by Dr. Brian Staiger, PharmD · September 2022 ›

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Acyclovir

This page covers Saccharomyces Boulardii only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Acyclovir page lists 37 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Asarabacca (major), Siberian Cocklebur (major), African Wild Potato (moderate) and Aristolochia (moderate).

By severity: 3 major · 23 moderate · 11 minor.

From our pharmacist’s overview on the Acyclovir page

“Kidney strain is the risk to understand first. Acyclovir (Zovirax) can stress the kidneys on its own, and a few ingredients here, Siberian cocklebur especially, are toxic to kidney tissue, so pairing them could compound the harm.”

Reviewed by 2 · Jul 18, 2026

Open the Acyclovir interaction page

One more smart check

Taking Saccharomyces Boulardii as Part of a Dietary Supplement Product? Check It for Interactions

We hold 608 real supplement products containing Saccharomyces Boulardii, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Saccharomyces Boulardii. Even though Saccharomyces Boulardii itself has no known interaction with Acyclovir, another ingredient on your label might. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Saccharomyces Boulardii and Acyclovir Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Saccharomyces Boulardii

Top 25%

#248 of 1,452 supplements looked up here in the last 7 days

29 days ago today

Medication Acyclovir

Top 5%

#59 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Where does our data come from?

Source: the Natural Medicines (TRC Healthcare) clinical database — the evidence-graded professional reference for herb & supplement interactions.
Citation library: 103,510 references behind our interaction content, 65,311 of them resolved to verified PubMed/DOI sources. See every Saccharomyces Boulardii reference on this page ↓
Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The Saccharomyces Boulardii and Acyclovir records this page draws on were last updated July 10, 2026.
What “no known interaction” means: no documented interaction in the sources above — not a guarantee of safety. Supplements are studied far less than prescription drugs, so we say exactly what the evidence supports, and nothing more.

Data structure & sourcing designed and verified by Dr. Brian Staiger, PharmD, BCPS.

Supplement

About Saccharomyces Boulardii

What is Saccharomyces Boulardii?

Acute diarrhea
Antibiotic-associated diarrhea
Traveler's diarrhea
Preventing C. difficile recurrence
General gut health

Saccharomyces boulardii is a beneficial yeast used as a probiotic, with the strongest evidence for preventing and treating certain types of diarrhea, including antibiotic-associated diarrhea. It is generally well tolerated in healthy people, but those who are seriously ill or have weakened immune systems should avoid it because of rare but serious bloodstream infections. Talk with your pharmacist or doctor before starting it.

Saccharomyces cerevisiae var. boulardii · Saccharomycetaceae · Whole yeast cells (probiotic microorganism) · Capsules, tablets, powders (often sold as lyophilized/freeze-dried yeast)

An interaction check asks whether these two react with each other — it does not ask whether Saccharomyces Boulardii is a good idea for someone in your situation. Here is what our Saccharomyces Boulardii record says about it on its own.

Saccharomyces Boulardii: dosing

There is no single official standardized dose for S. boulardii. Products are often measured in milligrams of freeze-dried yeast or in colony-forming units (CFU), and amounts vary widely between brands.The best approach is to follow the directions on the product label and to choose a reputable brand.

From our Saccharomyces Boulardii monograph — the full record covers uses, side effects and every documented interaction.

Read the full Saccharomyces Boulardii monograph & all interactions

Medication

About Acyclovir

What Is Acyclovir Used For?

Brand names: Zovirax, Zovirax Injection, Sitavig, Avaclyr

Acyclovir treats infections caused by herpes viruses. Depending on the form, it is used for cold sores (herpes labialis), genital herpes (initial episodes and recurrent flare-ups), shingles (herpes zoster), and chickenpox (varicella). It can also be used long-term to suppress recurrent genital herpes outbreaks.

Some forms are approved for more serious situations: acyclovir injection is used in hospital settings for herpes simplex encephalitis (herpes infection of the brain), neonatal herpes (in newborns), and herpes or shingles infections in immunocompromised patients. Avaclyr ophthalmic ointment is specifically indicated for acute herpetic keratitis (a herpes ulcer on the cornea of the eye). Sitavig buccal tablet and Zovirax cream are specifically indicated for recurrent cold sores in immunocompetent adults.

Most-Reported Side Effects for Acyclovir

From FAERS, the FDA’s public side-effect reporting system (114,761 reports, all brands). Reports are voluntary and are not proof the drug caused the effect.

Fatigue 8,029 reports

Diarrhea 7,348 reports

Pneumonia 5,700 reports

Nausea 5,643 reports

Fever 4,989 reports

See full Acyclovir drug information

Keep checking

Other Drugs & Saccharomyces Boulardii

Browse every other medication we’ve checked against Saccharomyces Boulardii — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major

0Moderate

40Minor

2,789No known interaction

40 Minor 2,789 No interaction

Minor

40 interactions

No interaction 2,789 drugs checked — show the list

We also checked Saccharomyces Boulardii against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,789 medications checked with no known interaction — see the full Saccharomyces Boulardii list.

See the full Saccharomyces Boulardii interactions page

See every supplement checked against Acyclovir, ranked by severity

Evidence & sources

Saccharomyces Boulardii References

The 26 references that drive our Saccharomyces Boulardii monograph and interaction data, from the evidence-graded Natural Medicines (TRC Healthcare) database. Citations with a link open the study on PubMed or the publisher’s site.

Niault M, Thomas F, Prost J, et al. Fungemia due to Saccharomyces species in a patient treated with enteral Saccharomyces boulardii. Clin Infect Dis 1999;28:930.
Pletinex M, Legein J, Vandenplas Y. Fungemia with Saccharomyces boulardii in a 1-year-old girl with protracted diarrhea. J Pediatr Gastroenterol Nutr 1995;21:113-5. DOI
Fredenucci I, Chomarat M, Boucaud C, et al. Saccharomyces boulardii fungemia in a patient receiving ultra-levure therapy. Clin Infect Dis 1998;27:222-3.
Elmer GW, McFarland LV, Surawicz CM, et al. Behaviour of Saccharomyces boulardii in recurrent Clostridium difficile disease patients. Aliment Pharmacol Ther 1999;13:1663-8.
Lewis SJ, Freedman AR. Review article: the use of biotherapeutic agents in the prevention and treatment of gastrointestinal disease. Aliment Pharmacol Ther 1998;12:807-22. PubMed
Cesaro S, Chinello P, Rossi L, Zanesco L. Saccharomyces cerevisiae fungemia in a neutropenic patient treated with Saccharomyces boulardii. Support Care Cancer 2000;8:504-5. PubMed
Hennequin C, Thierry A, Richard GF, et al. Microsatellite typing as a new tool for identification of Saccharomyces cerevisiae strains. J Clin Microbiol 2001;39:551-9.
Plein K, Hotz J. Therapeutic effects of Saccharomyces boulardii on mild residual symptoms in a stable phase of Crohn's disease with special respect to chronic diarrhea - a pilot study. Z Gastroenterol 1993;31:129-34.
Borriello SP, Hammes WP, Holzapfel W, et al. Safety of probiotics that contain lactobacilli or bifidobacteria. Clin Infect Dis 2003;36:775-80. PubMed
Marteau P, Seksik P. Tolerance of probiotics and prebiotics. J Clin Gastroenterol 2004;38:S67-9. PubMed
Munoz P, Bouza E, Cuenca-Estrella M, et al. Saccharomyces cerevisiae fungemia: an emerging infectious disease. Clin Infect Dis 2005;40:1625-34. PubMed
Lherm, T., Monet, C., Nougiere, B., Soulier, M., Larbi, D., Le Gall, C., Caen, D., and Malbrunot, C. Seven cases of fungemia with Saccharomyces boulardii in critically ill patients. Intensive Care Med 2002;28(6):797-801. PubMed
Riquelme, A. J., Calvo, M. A., Guzman, A. M., Depix, M. S., Garcia, P., Perez, C., Arrese, M., and Labarca, J. A. Saccharomyces cerevisiae fungemia after Saccharomyces boulardii treatment in immunocompromised patients. J Clin.Gastroenterol. 2003;36(1):41- PubMed
Cherifi, S., Robberecht, J., and Miendje, Y. Saccharomyces cerevisiae fungemia in an elderly patient with Clostridium difficile colitis. Acta Clin Belg. 2004;59(4):223-224. PubMed
Ellouze O, Berthoud V, Mervant M, Parthiot JP, Girard C. Septic shock due to Sacccaromyces boulardii. Med Mal Infect. 2016;46(2):104-105.
Appel-da-Silva MC, Narvaez GA, Perez LRR, Drehmer L, Lewgoy J. Saccharomyces cerevisiae var. boulardii fungemia following probiotic treatment. Med Mycol Case Rep. 2017;18:15-7. PubMed
Atici S, Soysal A, Karadeniz Cerit K, et al. Catheter-related Saccharomyces cerevisiae Fungemia Following Saccharomyces boulardii Probiotic Treatment: In a child in intensive care unit and review of the literature. Med Mycol Case Rep. 2017;15:33-35. PubMed
Martin IW, Tonner R, Trivedi J, et al. Saccharomyces boulardii probiotic-associated fungemia: questioning the safety of this preventive probiotic's use. Diagn Microbiol Infect Dis. 2017;87(3):286-8. PubMed
Romanio MR, Coraine LA, Maielo VP, Abramczyc ML, Souza RL, Oliveira NF. Saccharomyces cerevisiae fungemia in a pediatric patient after treatment with probiotics. Rev Paul Pediatr 2017;35(3):361-4.
Roy U, Jessani LG, Rudramurthy SM, et al. Seven cases of Saccharomyces fungaemia related to use of probiotics. Mycoses 2017;60(6):375-380.
Romanio MR, Coraine LA, Maielo VP, Abramczyc ML, Souza RL, Oliveira NF. Saccharomyces cerevisiae fungemia in a pediatric patient after treatment with probiotics. Rev Paul Pediatr. 2017 Jul-Sep;35(3):361-364. doi: 10.1590/1984-0462/;2017;35;3;00014.
Flatley EA, Wilde AM, Nailor MD. Saccharomyces boulardii for the prevention of hospital onset Clostridium difficile infection. J Gastrointestin Liver Dis. 2015;24(1):21-4. PubMed
Ventoulis I, Sarmourli T, Amoiridou P, et al. Bloodstream infection by Saccharomyces cerevisiae in two COVID-19 patients after receiving supplementation of Saccharomyces in the ICU. J Fungi (Basel). 2020;6(3):98. PubMed
Wombwell E, Bransteitter B, Gillen LR. Incidence of Saccharomyces cerevisiae fungemia in hospitalised patients administered Saccharomyces boulardii probiotic. Mycoses 2021;64(12):1521-1526.
Rannikko J, Holmberg V, Karppelin M, et al. Fungemia and Other Fungal Infections Associated with Use of Saccharomyces boulardii Probiotic Supplements. Emerg Infect Dis 2021;27(8):2090-6.
Awoyemi A, Mayerhofer C, Felix AS, et al. Rifaximin or Saccharomyces boulardii in heart failure with reduced ejection fraction: Results from the randomized GutHeart trial. EBioMedicine 2021;70:103511. PubMed

Medication overviews come from MedlinePlus (NIH); supplement label data from the NIH Dietary Supplement Label Database. Content is written and reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

Pharmacist Counseling Corner

Taking Saccharomyces Boulardii and Acyclovir Together: Common Questions

Is it safe to take Saccharomyces Boulardii with Acyclovir?

We do not list a known interaction between Saccharomyces Boulardii and Acyclovir. That does not guarantee the combination is risk-free, so confirm with your pharmacist or doctor — especially if you take other medications or have a health condition.

Do Saccharomyces Boulardii and Acyclovir have any of the same side effects?

Yes — our sources link each of them separately to 4 of the same effects. That is not an interaction: neither changes how your body handles the other. It does mean that if one of those effects turns up, it can be harder to tell which one is behind it. They are listed on this page with the source behind each.

How was the Saccharomyces Boulardii and Acyclovir combination checked?

Interactions in our licensed database are recorded against drug classes. Acyclovir is filed under 6 classifications, and Saccharomyces Boulardii has documented interactions with 1 drug class — none of Acyclovir's classifications are among them. A medication can belong to classes beyond those recorded in our dataset, so this describes how the check was run rather than guaranteeing safety.

Does Saccharomyces Boulardii interact with any other medications?

Yes. Saccharomyces Boulardii has 40 documented drug interactions in our database — Acyclovir is simply not one of them. If you take anything else, it is worth checking each one; they are all listed on this page.

Does Acyclovir interact with any supplements?

Yes. Acyclovir has documented interactions with 37 supplements in our database — Saccharomyces Boulardii is not one of them. The Acyclovir interaction page linked on this page lists every one, ranked by severity.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Where next

Keep Exploring

Saccharomyces Boulardii monograph Uses, safety profile, and every drug interaction in one place Acyclovir drug information The full plain-English guide to this medication Acyclovir supplement interactions Every supplement checked against Acyclovir, ranked by severity Supplement interaction checker Check any supplement or product against your medications Browse medications A–Z Every drug we’ve checked against herbs & supplements References The 26 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Acyclovir and Saccharomyces Boulardii?

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.