Drug & supplement interaction

Flaxseed + Nitrofurantoin

Nitrofurantoin brand names: Macrodantin, Furadantin, Furatoin, Macrobid.

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

Flaxseed has a moderate interaction with Nitrofurantoin. Theoretically, antibiotics might interfere with the metabolism of flaxseed constituents, which could potentially alter the effects of flaxseed.

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

Flaxseed and Nitrofurantoin

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

Moderate

ANTIBIOTIC DRUGS

Why this applies to Nitrofurantoin

Nitrofurantoin falls under ANTIBIOTIC DRUGS — the group Flaxseed interacts with.

Theoretically, antibiotics might interfere with the metabolism of flaxseed constituents, which could potentially alter the effects of flaxseed.
Some potential benefits of flaxseed are thought to be due to its lignan content. Secoisolariciresinol diglucoside (SDG), a major lignan precursor, is found in high concentrations in flaxseed. SDG is converted by bacteria in the colon to the lignans enterolactone and enterodiol. Antibiotics alter the flora of the colon, which could theoretically alter the metabolism of flaxseed.
Severity Moderate Likelihood Possible Evidence D

Interaction 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.

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

Here's the thing to understand about this pairing: the worry isn't that flaxseed changes how your nitrofurantoin works, and it isn't that the antibiotic causes more bladder-infection side effects. It actually runs the other direction. Flaxseed's lignan precursors need friendly gut bacteria in your colon to turn them into the active compounds (enterolactone and enterodiol) that some of flaxseed's benefits are tied to.

Since nitrofurantoin can shift the balance of those gut bacteria, it could, in theory, blunt some of flaxseed's effects during your short course of treatment. This is purely a pharmacology guess, not something proven in people, so I wouldn't lose sleep over it. Flaxseed as a food is fine, and nitrofurantoin still treats your infection normally. If you have questions, just check with your pharmacist.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Thompson LU, Rickard SE, Cheung F, et al. Variability in anticancer lignan levels in flaxseed. Nutr Cancer 1997;27:26-30. PubMed
  2. Serraino M, Thompson LU. The effect of flaxseed supplementation on early risk markers for mammary carcinogenesis. Cancer Lett 1991;60:135-42. PubMed
  3. Rickard SE, Yuan YV, Thompson LU. Plasma insulin-like growth factor I levels in rats are reduced by dietary supplementation of flaxseed or its lignan secoisolariciresinol diglycoside. Cancer Lett 2000;161:47-55. PubMed
  4. Adlercreutz H, Fotsis T, Bannwart C, et al. Determination of urinary lignans and phytoestrogen metabolites, potential antiestrogens and anticarcinogens, in urine of women on various habitual diets. J Steroid Biochem 1986;25:791-7.. 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

Flaxseed Also Interacts With Other Medications

Flaxseed has 596 moderate known drug interactions in our database — the Nitrofurantoin one above is one of them. If you take anything else, check it against the full list below.

Moderate 596 No known interaction 2,234 (incl. Nitrofurantoin)
Taking anything else?

Check Another of Your Medications Against Flaxseed

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

From our Q&A

Questions About Flaxseed or Nitrofurantoin

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Flaxseed or Nitrofurantoin, 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 Nitrofurantoin

This page covers Flaxseed only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Nitrofurantoin page lists 82 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Beer (major), Siberian Cocklebur (major), Wine (major) and Ashwagandha (moderate).

By severity: 4 major · 68 moderate · 10 minor.

From our pharmacist’s overview on the Nitrofurantoin page

“Nitrofurantoin (Macrobid, Macrodantin) treats urinary tract infections and can strain the liver on its own, which is why this interaction list deserves genuine care rather than a glance. Of the 82 ingredients on file, 38 can add their own liver stress on top of the drug's, and three of the four major-rated entries fall in that group, i…”

Reviewed by 2 · Jul 18, 2026

Open the Nitrofurantoin interaction page

One more smart check

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

We hold 236 real supplement products containing Flaxseed, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Flaxseed. Your product may carry other ingredients that interact with Nitrofurantoin too, on top of Flaxseed — 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 Flaxseed and Nitrofurantoin 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 Flaxseed
Top 25%

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

29 days ago today
Medication Nitrofurantoin
Top 25%

#373 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 Flaxseed

What is Flaxseed?

Flaxseed
  • Constipation and digestive health
  • High cholesterol
  • Heart health
  • Menopausal symptoms
  • Blood sugar support

Flaxseed is a nutritious food rich in fiber, omega-3 fats (ALA), and plant compounds called lignans. It is most reliably helpful for constipation and may modestly lower cholesterol, but evidence for many other uses is mixed or limited. It is generally safe as a food, but talk to your pharmacist or doctor before using it as a supplement, especially if you are pregnant or breastfeeding.

Read the full Flaxseed monograph & all interactions
Medication

About Nitrofurantoin

What Is Nitrofurantoin Used For?

Brand names: Macrodantin, Furadantin, Furatoin, Macrobid

Nitrofurantoin treats urinary tract infections (UTIs) caused by specific susceptible bacteria. The capsule forms (including Macrodantin and nitrofurantoin macrocrystals capsules) are indicated for UTIs due to Escherichia coli, enterococci, Staphylococcus aureus, and certain strains of Klebsiella and Enterobacter species. Nitrofurantoin capsules (monohydrate/macrocrystals) are indicated only for acute uncomplicated UTIs (acute cystitis) caused by E. coli or Staphylococcus saprophyticus.

Nitrofurantoin oral suspension (Furadantin) is indicated for adults and children 1 month of age and older for UTIs caused by susceptible strains of E. coli, Enterococcus species, S. aureus, Klebsiella species, and Enterobacter species. No form of nitrofurantoin is approved for kidney infections (pyelonephritis) or infections in the tissue surrounding the kidneys (perinephric abscesses).

See full Nitrofurantoin drug information
Keep checking

Other Drugs & Flaxseed

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

0Major
596Moderate
0Minor
2,233No known interaction
596 Moderate 2,233 No interaction
Moderate

596 interactions

Showing 60 of 596 moderate interactions — see all 596 on the Flaxseed page.

No interaction 2,233 drugs checked — show the list

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

Showing the 60 most looked-up of 2,233 medications checked with no known interaction — see the full Flaxseed list.

See the full Flaxseed interactions page
See every supplement checked against Nitrofurantoin, 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
Flaxseed monograph › Uses, safety, and every drug interaction in one place Nitrofurantoin supplement interactions › Every supplement checked against Nitrofurantoin, ranked by severity Nitrofurantoin drug information › The full plain-English guide to this medication 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 Flaxseed and Nitrofurantoin Together: Common Questions

Can you take Flaxseed with Nitrofurantoin?
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 Flaxseed and Nitrofurantoin 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 Nitrofurantoin and Flaxseed?

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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.