Drug & supplement interaction

Antineoplastons + 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 Antineoplastons 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. 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

Antineoplastons 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 Antineoplastons 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.

Worth understanding: our licensed dataset holds no drug-interaction record for Antineoplastons at all — not against Letrozole, and not against any other medication we track. This verdict therefore rests on the absence of any recorded data, not on research that looked at this combination and found nothing. We cannot rule an interaction out.

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.

Antineoplastons safety at a glance

Antineoplastons overall Use caution Not FDA-approved; effectiveness is unproven and side effects can be serious, especially at high doses.
Pregnancy Avoid There is no reliable safety data, so use during pregnancy should be avoided.
Breastfeeding Avoid Safety while breastfeeding is unknown, so it should be avoided.

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

Still wondering about combining Letrozole and Antineoplastons? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
What to actually watch for

No Interaction Found — But Data Suggests Antineoplastons and Letrozole 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.

  • Joint pain / Swelling Additional detail

    Antineoplastons

    “Orally and intravenously, antineoplastons AS2-1 and A10 have been associated with peripheral edema. Swelling of joints, muscle and joint pain, muscle contractions in the throat, weakness, and fatigue have been reported for patients treated with antineoplastons A2, AS2-1, AS2-5, and/or A10.”

    Antineoplastons · Natural Medicines adverse-effect record, reported in fatigue.

    5 sources cited
    1. 25604. Tsuda H, Hara H, Eriguchi N, et al. Toxicological study on antineoplastons A-10 and AS2-1 in cancer patients. Kurume Med J 1995;42(4):241-249. PubMed
    2. 25624. Burzynski SR. Toxicology studies on antineoplaston AS2-5 injections in cancer patients. Drugs Exp Clin Res 1986;12 Suppl 1:17-24.
    3. 25603. Burzynski SR, Lewy RI, Weaver RA, et al. Phase II study of antineoplaston A10 and AS2-1 in patients with recurrent diffuse intrinsic brain stem glioma: a preliminary report. Drugs R D 2003;4(2):91-101. PubMed
    4. 25620. Burzynski SR, Kubove E. Toxicology studies on antineoplaston A10 injections in cancer patients. Drugs Exp Clin Res 1986;12 Suppl 1:47-55.
    5. 25621. Burzynski SR, Kubove E. Initial clinical study with antineoplaston A2 injections in cancer patients with five years' follow-up. Drugs Exp Clin Res 1987;13 Suppl 1:1-11.

    Letrozole

    Listed in the ADVERSE REACTIONS section of the FDA label for Letrozole. Read the label on DailyMed ›

  • Tiredness Additional detail

    Antineoplastons

    “Orally and intravenously, headache, fatigue, sleepiness, ringing in the ears, and numbness have been reported for patients treated with antineoplastons A10 and AS2-1. Dizziness has also been noted for some patients treated with oral antineoplaston A10 or intravenous antineoplaston A3.”

    Antineoplastons · Natural Medicines adverse-effect record, reported in cluster headache.

    6 sources cited
    1. 25593. Buckner JC, Malkin MG, Reed E, et al. Phase II study of antineoplastons A10 (NSC 648539) and AS2-1 (NSC 620261) in patients with recurrent glioma. Mayo Clin Proc 1999;74(2):137-145. PubMed
    2. 25601. Burzynski SR, Conde AB, Peters A, et al. A retrospective study of antineoplastons A10 and AS2-1 in primary brain tumors. Clin Drug Invest 1999;18(1):1-10.
    3. 25603. Burzynski SR, Lewy RI, Weaver RA, et al. Phase II study of antineoplaston A10 and AS2-1 in patients with recurrent diffuse intrinsic brain stem glioma: a preliminary report. Drugs R D 2003;4(2):91-101. PubMed
    4. 25610. Burzynski SR, Weaver RA, Lewy RI, et al. Phase II study of antineoplaston A10 and AS2-1 in children with recurrent and progressive multicentric glioma : a preliminary report. Drugs R D 2004;5(6):315-326. PubMed
    5. 25620. Burzynski SR, Kubove E. Toxicology studies on antineoplaston A10 injections in cancer patients. Drugs Exp Clin Res 1986;12 Suppl 1:47-55.
    6. 20101. Burzynski SR, Mohabbat MO, Burzynski B. Human toxicology studies on oral formulation of Antineoplaston A10. Drugs Exp Clin Res 1984;10(12):891-909.

    Letrozole

    Listed in the ADVERSE REACTIONS section of the FDA label for Letrozole. Read the label on DailyMed ›

  • Dizziness / Headache Additional detail

    Antineoplastons

    Recorded for Antineoplastons in the same Natural Medicines adverse-effect record shown under Tiredness above.

    Letrozole

    Listed in the ADVERSE REACTIONS section of the FDA label for Letrozole. Read the label on DailyMed ›

  • Nausea Additional detail

    Antineoplastons

    “Orally, nausea, vomiting, upset stomach, abdominal pain, and excessive flatulence has been reported for patients with neoplastic disease treated with antineoplaston A10 100-149 mg/kg/day for up to 149 days.”

    Antineoplastons · Natural Medicines adverse-effect record, reported in flatulence.

    2 sources cited
    1. 20101. Burzynski SR, Mohabbat MO, Burzynski B. Human toxicology studies on oral formulation of Antineoplaston A10. Drugs Exp Clin Res 1984;10(12):891-909.
    2. 25620. Burzynski SR, Kubove E. Toxicology studies on antineoplaston A10 injections in cancer patients. Drugs Exp Clin Res 1986;12 Suppl 1:47-55.

    Letrozole

    Listed in the ADVERSE REACTIONS section of the FDA label for Letrozole. Read the label on DailyMed ›

Reported for Antineoplastons but not commonly for Letrozole: an irregular heartbeat, ringing in the ears, stomach pain and chest pain.

Effects for Letrozole come from the ADVERSE REACTIONS section of its FDA label; effects for Antineoplastons come from the Natural Medicines adverse-effect record, quoted above. 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 Antineoplastons 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 Antineoplastons 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 Antineoplastons 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

How much people look this up

Where Antineoplastons 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 Antineoplastons
Steady interest

#1,291 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 Antineoplastons reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The Antineoplastons 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 Antineoplastons

What is Antineoplastons?

  • Cancer (various types, including brain tumors)
  • Adjunct cancer support
  • Investigational anticancer therapy

Antineoplastons are synthetic peptide and amino acid compounds promoted as an alternative cancer treatment, but they are not approved by the FDA and high-quality clinical evidence supporting their effectiveness is lacking. Most studies have been conducted by their developer and have not been independently confirmed. If you are considering them, talk with your oncologist first, and never replace proven cancer treatment with an unproven one.

Synthetic peptides, amino acid derivatives, and organic acids (originally isolated from human blood and urine) · Oral capsules and intravenous (IV) infusions, used mainly within specific clinics or research settings

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

Antineoplastons: dosing

There is no established, standardized safe dose of antineoplastons for any condition, and they are not available as a regular over-the-counter supplement. The doses studied have varied widely and were given under medical supervision, often as intravenous infusions.Because these products are unproven and can cause serious side effects, you should not try to dose them on your own. If you are considering antineoplastons, discuss it thoroughly with your oncologist and pharmacist first.

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

Read the full Antineoplastons 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 & Antineoplastons

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

0Major
0Moderate
0Minor
2,829No known interaction
2,829 No interaction
No interaction 2,829 drugs checked — show the list

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

Showing the 60 most looked-up of 2,829 medications checked with no known interaction — see the full Antineoplastons list.

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

Antineoplastons References

The 20 references that drive our Antineoplastons 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. Burzynski SR, Stolzmann Z, Szopa B, Stolzmann E, Kaltenberg OP. Antineoplaston A in cancer therapy. (I). Physiol Chem Phys 1977;9(6):485-500.
  2. Burzynski SR, Mohabbat MO, Burzynski B. Human toxicology studies on oral formulation of Antineoplaston A10. Drugs Exp Clin Res 1984;10(12):891-909.
  3. Burzynski SR, Kubove E, Burzynski B. Treatment of hormonally refractory cancer of the prostate with antineoplaston AS2-1. Drugs Exp Clin Res 1990;16(7):361-369.
  4. Buckner JC, Malkin MG, Reed E, et al. Phase II study of antineoplastons A10 (NSC 648539) and AS2-1 (NSC 620261) in patients with recurrent glioma. Mayo Clin Proc 1999;74(2):137-145. PubMed
  5. Burzynski SR, Conde AB, Peters A, et al. A retrospective study of antineoplastons A10 and AS2-1 in primary brain tumors. Clin Drug Invest 1999;18(1):1-10.
  6. Burzynski SR, Lewy RI, Weaver RA, et al. Phase II study of antineoplaston A10 and AS2-1 in patients with recurrent diffuse intrinsic brain stem glioma: a preliminary report. Drugs R D 2003;4(2):91-101. PubMed
  7. Tsuda H, Hara H, Eriguchi N, et al. Toxicological study on antineoplastons A-10 and AS2-1 in cancer patients. Kurume Med J 1995;42(4):241-249. PubMed
  8. Burzynski SR, Kubove E. Phase I clinical studies of antineoplaston A3 injections. Drugs Exp Clin Res 1987;13 Suppl 1:17-29.
  9. Burzynski SR, Kubove E, Burzynski B. Phase I clinical studies of antineoplaston A5 injections. Drugs Exp Clin Res 1987;13 Suppl 1:37-43.
  10. Burzynski SR, Weaver RA, Lewy RI, et al. Phase II study of antineoplaston A10 and AS2-1 in children with recurrent and progressive multicentric glioma : a preliminary report. Drugs R D 2004;5(6):315-326. PubMed
  11. Burzynski SR, Weaver RA, Janicki T, et al. Long-term survival of high-risk pediatric patients with primitive neuroectodermal tumors treated with antineoplastons A10 and AS2-1. Integr Cancer Ther 2005;4(2):168-177. PubMed
  12. Burzynski SR, Burzynski B, Mohabbat MO. Toxicology studies on antineoplaston AS2-1 injections in cancer patients. Drugs Exp Clin Res 1986;12 Suppl 1:25-35.
  13. Burzynski SR, Kubove E. Toxicology studies on antineoplaston A10 injections in cancer patients. Drugs Exp Clin Res 1986;12 Suppl 1:47-55.
  14. Burzynski SR, Kubove E. Initial clinical study with antineoplaston A2 injections in cancer patients with five years' follow-up. Drugs Exp Clin Res 1987;13 Suppl 1:1-11.
  15. Burzynski SR, Kubove E, Burzynski B. Phase I clinical studies of antineoplaston A5 injections. Drugs Exp Clin Res 1987;13 Suppl 1:37-43.

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 Antineoplastons and Letrozole Together: Common Questions

Is it safe to take Antineoplastons with Letrozole?
We do not list a known interaction between Antineoplastons 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.
Do Antineoplastons and Letrozole have any of the same side effects?
Yes — our sources link each of them separately to 6 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.
Does Letrozole interact with any supplements?
Yes. Letrozole has documented interactions with 142 supplements in our database — Antineoplastons 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

Antineoplastons 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 20 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Letrozole and Antineoplastons?

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.