Drug & supplement interaction

Borage + Letrozole

Letrozole brand name: Femara.

No Known Interaction
Medically reviewed by · Updated July 2026 · Pair last verified Sep 13, 2026
The bottom line No known interaction

We found no known interaction between Borage and Letrozole 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.

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Interaction report

Borage and Letrozole

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 Letrozole and Borage 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.

Borage safety at a glance

Borage overall Use caution Seed oil that is certified pyrrolizidine alkaloid (PA)-free is generally better tolerated, but other parts may harm the liver.
Pregnancy Likely Unsafe When products containing hepatotoxic pyrrolizidine alkaloids (PA) are used orally. Borage plant parts, such as the leaf, flower, and seed, can contain hepatotox... Read the full pregnancy detail
Breastfeeding Likely Unsafe When products containing hepatotoxic pyrrolizidine alkaloids (PA) are used orally. Borage plant parts, such as the leaf, flower, and seed, can contain hepatotox... Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center) — the full detail is in the Special populations card below. Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Letrozole and Borage? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
How we checked

Why No Interaction Is Listed for Letrozole

Interactions in our licensed database are recorded against drug classes, not just single drug names. Letrozole is filed under 4 classifications — including aromatase inhibitors, cytochrome p450 2c19 (cyp2c19) inhibitors, cytochrome p450 3a4 (cyp3a4) substrates. Borage has documented interactions with 3 drug classes — the most serious being anticoagulant/antiplatelet drugs (moderate), cytochrome p450 3a4 (cyp3a4) inducers (moderate) and phenothiazines (moderate) — and none of Letrozole’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

Borage Does Interact With Other Medications

Borage has 226 moderate known drug interactions in our database — Letrozole isn’t one of them. If you take anything else, check it against the full list below.

Moderate 226 No known interaction 2,604 (incl. Letrozole)
Taking anything else?

Check Another of Your Medications Against Borage

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

What to actually watch for

What Borage Itself Has Been Linked To

This is not an interaction — nothing below involves Letrozole. It is the side-effect record for Borage on its own, from the licensed Natural Medicines monograph. If something new turns up after you add Borage, this list is the first place to look. One entry is worth acting on rather than waiting out — marked below.

  • Liver problems Worth acting on Additional detail

    “The pyrrolizidine alkaloid (PA) constituents of borage can cause significant hepatotoxicity. PAs can occur in borage leaf, flower, and seed; borage seed oil contains little to no PAs. Chronic exposure to other plants containing hepatotoxic PA constituents has been associated with veno-occlusive disease (VOD). Subacute VOD causes vague symptoms with persistent liver enlargement.”

    Borage · Natural Medicines adverse-effect record, reported in diarrhea.

    3 sources cited
    1. 12841. Chojkier M. Hepatic sinusoidal-obstruction syndrome: toxicity of pyrrolizidine alkaloids. J Hepatol 2003;39:437-46. PubMed
    2. 12842. Roeder E. Medicinal plants in Europe containing pyrrolizidine alkaloids. Pharmazie 1995;50:83-98.
    3. 4021. WHO working group. Pyrrolizidine alkaloids. Environmental Health Criteria, 80. WHO: Geneva, 1988.
  • Bloating or gas / Diarrhea Additional detail

    “Orally, borage seed oil can cause soft stools, diarrhea, belching, and bloating.”

    Borage · Natural Medicines adverse-effect record, reported in diarrhea.

    2 sources cited
    1. 8013. Fan YY, Chapkin RS. Importance of dietary gamma-linolenic acid in human health and nutrition. J Nutr 1998;128:1411-4.
    2. 11341. Takwale A, Tan E, Agarwal S, et al. Efficacy and tolerability of borage oil in adults and children with atopic eczema: randomised, double blind, placebo controlled, parallel group trial. BMJ 2003;327:1385. PubMed
  • Vomiting Additional detail

    Recorded for Borage in the same Natural Medicines adverse-effect record shown under Liver problems above.

Everything above comes from the Natural Medicines adverse-effect record for Borage — expand a row for the licensed statement it rests on. We read the ADVERSE REACTIONS section of Letrozole’s FDA label too, and the two lists don’t meaningfully overlap — which is why no Letrozole column appears here.

Special populations

Borage in Pregnancy & Breastfeeding

Pregnancy And Lactation Likely Unsafe

When products containing hepatotoxic pyrrolizidine alkaloids (PA) are used orally. Borage plant parts, such as the leaf, flower, and seed, can contain hepatotoxic PAs. Repeated exposure to low concentrations of hepatotoxic PAs can cause severe veno-occlusive disease. Hepatotoxic PAs might also be carcinogenic, mutagenic, and teratogenic. These constituents are also excreted in breast milk. Tell patients to avoid borage preparations that are not certified and labeled as hepatotoxic PA-free. There is insufficient reliable information available about the safety of borage seed oil when used orally or topically during pregnancy or lactation.

DISCLAIMER: This tool is intended for informational purposes only, and should not be interpreted as specific medical advice. Patients should consult with a qualified healthcare provider before making decisions about therapies and/or health conditions.© 2026 Therapeutic Research Center

From our Q&A

Questions About Borage or Letrozole

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

This page covers Borage only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Letrozole page lists 142 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Grapefruit (major), St. John's Wort (major), 7-methoxyflavone (moderate) and Acacia Rigidula (moderate).

By severity: 3 major · 99 moderate · 40 minor.

From our pharmacist’s overview on the Letrozole page

“Letrozole (Femara) is prescribed to keep hormone-driven breast cancer from returning, so a supplement that shifts its blood level can quietly undercut treatment. Give this list of 142 ingredients genuine respect, and learn the three major entries first.”

Reviewed by 2 · Jul 18, 2026

Open the Letrozole interaction page

One more smart check

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

We hold 122 real supplement products containing Borage, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Borage. Even though Borage itself has no known interaction with Letrozole, 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 Borage and Letrozole 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 Borage
Top 25%

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

29 days ago today
Medication Letrozole
Top 5%

#50 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 Borage reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The Borage and Letrozole 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 .
Supplement

About Borage

What is Borage?

Borage
  • Eczema and dry skin
  • Rheumatoid arthritis
  • Inflammation
  • Respiratory complaints
  • Mood and stress

Borage is a Mediterranean herb whose seed oil is rich in gamma-linolenic acid (GLA), an omega-6 fatty acid studied mostly for skin conditions and arthritis with mixed results. The plant's leaves and flowers can contain liver-toxic pyrrolizidine alkaloids, so only use products clearly labeled 'PA-free' and talk to your pharmacist or doctor before taking it.

Borago officinalis · Boraginaceae · Seeds (for oil), leaves, and flowers · Borage seed oil capsules, topical oil, tea, dried leaf/flower

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

Borage: dosing

There is no official, standardized dose of borage. Borage seed oil products are usually sold as capsules standardized to a certain amount of GLA, and the right amount can vary by product and purpose.The safest approach is to follow the directions on the product label and to choose a brand that states it is free of pyrrolizidine alkaloids.

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

Read the full Borage monograph & all interactions
Medication

About Letrozole

What Is Letrozole Used For?

Brand name: Femara

Letrozole (brand name Femara) is used to treat breast cancer in postmenopausal women whose tumors are driven by estrogen. It is used in three settings: as adjuvant (after-surgery) treatment for hormone receptor positive early breast cancer; as extended adjuvant treatment for women who have already completed about five years of tamoxifen therapy; and as first- or second-line treatment for locally advanced or metastatic (spread) breast cancer.

Femara is specifically indicated for first-line treatment of hormone receptor positive or receptor-unknown locally advanced or metastatic breast cancer, and for advanced breast cancer in women whose disease has progressed after antiestrogen therapy.

See full Letrozole drug information
Keep checking

Other Drugs & Borage

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

0Major
226Moderate
0Minor
2,603No known interaction
226 Moderate 2,603 No interaction
Moderate

226 interactions

Showing 60 of 226 moderate interactions — see all 226 on the Borage page.

No interaction 2,603 drugs checked — show the list

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

Showing the 60 most looked-up of 2,603 medications checked with no known interaction — see the full Borage list.

See the full Borage interactions page
See every supplement checked against Letrozole, ranked by severity
Evidence & sources

Borage References

The 11 references that drive our Borage 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.

  1. Guivernau M, Meza N, Barja P, Roman O. Clinical and experimental study on the long-term effect of dietary gamma-linolenic acid on plasma lipids, platelet aggregation, thromboxane formation, and prostacyclin production. Prostaglandins Leukot Essent Fatty A PubMed
  2. WHO working group. Pyrrolizidine alkaloids. Environmental Health Criteria, 80. WHO: Geneva, 1988.
  3. Fan YY, Chapkin RS. Importance of dietary gamma-linolenic acid in human health and nutrition. J Nutr 1998;128:1411-4.
  4. Takwale A, Tan E, Agarwal S, et al. Efficacy and tolerability of borage oil in adults and children with atopic eczema: randomised, double blind, placebo controlled, parallel group trial. BMJ 2003;327:1385. PubMed
  5. Chojkier M. Hepatic sinusoidal-obstruction syndrome: toxicity of pyrrolizidine alkaloids. J Hepatol 2003;39:437-46. PubMed
  6. Roeder E. Medicinal plants in Europe containing pyrrolizidine alkaloids. Pharmazie 1995;50:83-98.
  7. Wang YP, Yan J, Fu PP, Chou MW. Human liver microsomal reduction of pyrrolizidine alkaloid N-oxides to form the corresponding carcinogenic parent alkaloid. Toxicol Lett 2005;155:411-20. PubMed
  8. Holman CP and Bell AF. A trial of evening primrose oil in the treatment of chronic schizophrenia. J Orhtomolecular Psych 1983;12:302-304.
  9. Vaddadi KS. The use of gamma-linolenic acid and linoleic acid to differentiate between temporal lobe epilepsy and schizophrenia. Prostaglandins Med 1981;6(4):375-379. PubMed
  10. Bard, J. M., Luc, G., Jude, B., Bordet, J. C., Lacroix, B., Bonte, J. P., Parra, H. J., and Duriez, P. A therapeutic dosage (3 g/day) of borage oil supplementation has no effect on platelet aggregation in healthy volunteers. Fundam.Clin.Pharmacol. 1997;1
  11. Puri BK. The safety of evening primrose oil in epilepsy. Prostaglandins Leukotrienes Essential Fatty Acids 2007;77:101-3. 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 Borage and Letrozole Together: Common Questions

Is it safe to take Borage with Letrozole?
We do not list a known interaction between Borage and Letrozole. 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.
How was the Borage and Letrozole combination checked?
Interactions in our licensed database are recorded against drug classes. Letrozole is filed under 4 classifications, and Borage has documented interactions with 3 drug classes — none of Letrozole'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 Borage interact with any other medications?
Yes. Borage has 226 documented drug interactions in our database — Letrozole 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 Letrozole interact with any supplements?
Yes. Letrozole has documented interactions with 142 supplements in our database — Borage is not one of them. The Letrozole 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

Borage monograph Uses, safety profile, and every drug interaction in one place Letrozole drug information The full plain-English guide to this medication Letrozole supplement interactions Every supplement checked against Letrozole, 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 11 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Letrozole and Borage?

Our pharmacists answer your medication & supplement questions — free.

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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.