Drug & supplement interaction

Folic Acid + Pyrimethamine, Sulfadoxine

Pyrimethamine, Sulfadoxine brand name: Fansidar.

Moderate Interaction
Medically reviewed by · Updated October 2026
The bottom line Moderate

Folic Acid has a moderate interaction with Pyrimethamine, Sulfadoxine. Folic acid might antagonize the effects of pyrimethamine.

Read the full interaction report
SeverityModerate
LikelihoodProbable
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Folic Acid and Pyrimethamine, Sulfadoxine

Here is the interaction we found between these two, with the evidence behind it.

Moderate

PYRIMETHAMINE (Daraprim)

Folic acid might antagonize the effects of pyrimethamine.
Folic acid can antagonize the antiparasitic effects of pyrimethamine against toxoplasmosis and Pneumocystis carinii pneumonia. Folic acid doesn't antagonize the effects of pyrimethamine in the treatment of malaria, because malarial parasites cannot use exogenous folic acid. Use folinic acid as an alternative to folic acid when indicated.
Severity Moderate Likelihood Probable Evidence D

Interaction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports..

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the short version on Fansidar (pyrimethamine plus sulfadoxine) and folic acid. Pyrimethamine works by blocking a parasite's ability to use folate, basically starving it of the building blocks it needs to multiply. If you add extra folic acid, you may give those bugs an easier time, which could weaken how well the medicine fights infections like toxoplasmosis or Pneumocystis pneumonia.

Good news: this concern does not apply when the drug is used for malaria, since malaria parasites can't use the folic acid you swallow. When folate support is needed alongside this drug, doctors often choose folinic acid (leucovorin) instead. The evidence here is fairly anecdotal, so don't panic, but please check with your pharmacist or doctor before adding folic acid.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Van Delden C, Hirschel B. Folinic acid supplements to pyrimethamine-sulfadiazine for Toxoplasma encephalitis are associated with better outcome (letter). J Infect Dis 1996;173:1294-5. PubMed

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
  • PossibleInteraction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

Folic Acid Also Interacts With Other Medications

Folic Acid has 39 moderate known drug interactions in our database — the Pyrimethamine, Sulfadoxine one above is one of them. If you take anything else, check it against the full list below.

Moderate 39 No known interaction 2,791 (incl. Pyrimethamine, Sulfadoxine)
Taking anything else?

Check Another of Your Medications Against Folic Acid

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

From our Q&A

Questions About Folic Acid or Pyrimethamine, Sulfadoxine

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Folic Acid or Pyrimethamine, Sulfadoxine, 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:

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 Pyrimethamine, Sulfadoxine

This page covers Folic Acid only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Pyrimethamine, Sulfadoxine page lists 18 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Coffee Charcoal (moderate), European Mandrake (moderate), Glucomannan (moderate) and Guar Gum (moderate).

By severity: 1 major · 8 moderate · 9 minor.

From our pharmacist’s overview on the Pyrimethamine, Sulfadoxine page

“Someone taking Fansidar (pyrimethamine and sulfadoxine) for malaria is often also nursing an unsettled stomach, and activated charcoal, a common travel remedy for exactly that, is the one major-rated interaction here. Charcoal binds many medicines and can drag their blood levels down, and an underdosed antimalarial is a treatment that…”

Reviewed by 2 · Jul 18, 2026

Open the Pyrimethamine, Sulfadoxine interaction page

One more smart check

Taking Folic Acid as Part of a Dietary Supplement Product? Check It for Interactions

We hold 92 real supplement products containing Folic Acid, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Folic Acid. Your product may carry other ingredients that interact with Pyrimethamine, Sulfadoxine too, on top of Folic Acid — and those would not show on this page. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Folic Acid and Pyrimethamine, Sulfadoxine 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 Folic Acid
Top 25%

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

29 days ago today
Medication Pyrimethamine, Sulfadoxine
Top 25%

#421 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.

Supplement

About Folic Acid

What is Folic Acid?

  • Preventing neural tube birth defects
  • Treating or preventing folate deficiency
  • Supporting pregnancy health
  • Certain types of anemia
  • Heart and blood vessel health

Folic acid is the man-made form of vitamin B9 and is one of the most well-studied supplements, especially for preventing serious birth defects when taken before and during early pregnancy. It is widely available, inexpensive, and generally safe at recommended doses, but you should still check with your pharmacist or doctor about the right amount for you.

Read the full Folic Acid monograph & all interactions
Keep checking

Other Drugs & Folic Acid

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

0Major
39Moderate
0Minor
2,790No known interaction
39 Moderate 2,790 No interaction
Moderate

39 interactions

No interaction 2,790 drugs checked — show the list

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

Showing the 60 most looked-up of 2,790 medications checked with no known interaction — see the full Folic Acid list.

See the full Folic Acid interactions page
See every supplement checked against Pyrimethamine, Sulfadoxine, ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

Keep exploring
Folic Acid monograph › Uses, safety, and every drug interaction in one place Pyrimethamine, Sulfadoxine supplement interactions › Every supplement checked against Pyrimethamine, Sulfadoxine, 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 Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Folic Acid and Pyrimethamine, Sulfadoxine Together: Common Questions

Can you take Folic Acid with Pyrimethamine, Sulfadoxine?
There is a moderate interaction, so it may be acceptable with monitoring or timing changes — but check with your pharmacist first. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the Folic Acid and Pyrimethamine, Sulfadoxine interaction?
We rate it Moderate. This combination may require monitoring, a dose adjustment, or separating the times you take each one. Consult your pharmacist before using them together.

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

Still Have a Question About Pyrimethamine, Sulfadoxine and Folic Acid?

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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.