Drug & supplement interaction

1,4-butanediol + 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 1,4-butanediol 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

1,4-butanediol 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 1,4-butanediol 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.

1,4-butanediol safety at a glance

1,4-butanediol overall Avoid This is a toxic chemical that turns into GHB in the body and can be life-threatening.
Pregnancy Unsafe When used orally. Read the full pregnancy detail
Breastfeeding Unsafe When used orally. 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 1,4-butanediol? 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. 1,4-butanediol has documented interactions with 10 drug classes — the most serious being alcohol (ethanol) (major), cns depressants (major) and narcotic drugs (major) — 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

1,4-butanediol Does Interact With Other Medications

1,4-butanediol has 250 major, 21 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.

Major 250 Moderate 21 No known interaction 2,559 (incl. Letrozole)
Taking anything else?

Check Another of Your Medications Against 1,4-butanediol

Covers the 2,830 medications we’ve checked against 1,4-butanediol. Pick one to open its full report.

What to actually watch for

No Interaction Found — But Data Suggests 1,4-butanediol and Letrozole May Share a Side Effect

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.

  • Nausea Additional detail

    1,4-butanediol

    “Orally, 1,4-butanediol can cause nausea and vomiting, diarrhea, and fecal incontinence.”

    1,4-butanediol · Natural Medicines adverse-effect record, reported in diarrhea.

    5 sources cited
    1. 1318. Smith SW, Zvosec DL. Death and central nervous system depression after ingestion of 1.4-butanediol, a gamma-hydroxybutyrate-related dietary supplement. Ann Emerg Med 2000;36:S85.
    2. 3678. Anon. FDA alert on misuse of consumer products containing GHB, GBL and BD. Food and Drug Administration, Rockville, MD. June 15, 1999.
    3. 3679. Anon. Important message for health professionals: Report serious adverse events associated with dietary supplements containing GBL, GHB or BD. Food and Drug Administration, Rockville, MD. August 25, 1999. Available at: http://vm.cfsan.fda.gov/~dms/mwg
    4. 10640. Zvosec DL, Smith SW, McCutcheon JR, et al. Adverse events, including death, associated with the use of 1,4-butanediol. N Engl J Med. 2001;344:87-94.. PubMed
    5. 37465. Thai, D., Dyer, J. E., Jacob, P., and Haller, C. A. Clinical pharmacology of 1,4-butanediol and gamma-hydroxybutyrate after oral 1,4-butanediol administration to healthy volunteers. Clin.Pharmacol Ther. 2007;81(2):178-184. PubMed

    Letrozole

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

Reported for 1,4-butanediol but not commonly for Letrozole: dependence or withdrawal symptoms, chest pain, hallucinations and a slow heartbeat.

Effects for Letrozole come from the ADVERSE REACTIONS section of its FDA label; effects for 1,4-butanediol 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.

Special populations

1,4-butanediol in Pregnancy & Breastfeeding

Pregnancy And Lactation Unsafe

When used orally.

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 1,4-butanediol 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 1,4-butanediol 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 1,4-butanediol 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 1,4-butanediol 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 1,4-butanediol
Top half

#702 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 1,4-butanediol reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The 1,4-butanediol 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 1,4-butanediol

What is 1,4-butanediol?

  • Marketed illegally as a 'recreational' or party substance
  • Falsely sold as a sleep aid
  • Falsely promoted for bodybuilding or muscle growth
  • Industrial solvent and chemical manufacturing

1,4-butanediol is a toxic industrial chemical, not a safe dietary supplement. Once swallowed, the body converts it into GHB, a powerful central nervous system depressant that can cause coma, dangerous breathing problems, addiction, and death. It should never be taken as a supplement or recreational substance.

Synthetic industrial chemical (not a plant) · Liquid solvent (sometimes sold illegally as a 'supplement,' cleaner, or party drug)

An interaction check asks whether these two react with each other — it does not ask whether 1,4-butanediol is a good idea for someone in your situation. Here is what our 1,4-butanediol record says about it on its own.

1,4-butanediol: dosing

There is no established or recommended dose of 1,4-butanediol, because it is not a legitimate supplement or medicine. It should not be taken in any amount.If you have encountered a product that contains or is suspected to contain 1,4-butanediol, do not use it. In the U.S., you can reach Poison Control at 1-800-222-1222.

From our 1,4-butanediol monograph — the full record covers uses, side effects and every documented interaction.

Read the full 1,4-butanediol 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 & 1,4-butanediol

Browse every other medication we’ve checked against 1,4-butanediol — both the ones with a known interaction and the ones without. Select any drug for the full detail.

250Major
21Moderate
0Minor
2,558No known interaction
250 Major 21 Moderate 2,558 No interaction
Major

250 interactions

Showing 60 of 250 major interactions — see all 250 on the 1,4-butanediol page.

Moderate

21 interactions

No interaction 2,558 drugs checked — show the list

We also checked 1,4-butanediol against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,558 medications checked with no known interaction — see the full 1,4-butanediol list.

See the full 1,4-butanediol interactions page
See every supplement checked against Letrozole, ranked by severity
Evidence & sources

1,4-butanediol References

The 20 references that drive our 1,4-butanediol 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. Smith SW, Zvosec DL. Death and central nervous system depression after ingestion of 1.4-butanediol, a gamma-hydroxybutyrate-related dietary supplement. Ann Emerg Med 2000;36:S85.
  2. Anon. Adverse events associated with ingestion of gamma-butyrolactone--Minnesota, New Mexico, and Texas, 1998-1999. MMWR Morb Mortal Wkly Rep 1999;48:137-40.
  3. Harrington RD, Woodward JA, Hooton TM, et al. Life-threatening interactions between HIV-1 protease inhibitors and the illicit drugs MDMA and gamma-hydroxybutyrate. Arch Intern Med 1999;159:2221-4.
  4. Anon. FDA alert on misuse of consumer products containing GHB, GBL and BD. Food and Drug Administration, Rockville, MD. June 15, 1999.
  5. Anon. Important message for health professionals: Report serious adverse events associated with dietary supplements containing GBL, GHB or BD. Food and Drug Administration, Rockville, MD. August 25, 1999. Available at: http://vm.cfsan.fda.gov/~dms/mwg
  6. Anon. Multistate outbreak of poisonings associated with illicit use of gamma hydroxy butyrate. JAMA 1991;265:447-8. DOI
  7. Carotenuto A, De Feo V, Fattorusso E, et al. The flavonoids of Allium ursinum. Phytochem 1996;41:531-6. PubMed
  8. Ferrara SD, Tedeschi L, Frison G, Rossi A. Fatality due to gamma-hydroxybutyric acid (GHB) and heroin intoxication. J Forensic Sci 1995;40:501-4. DOI
  9. Timby N, Eriksson A. Gamma-Hydroxybutyrate-Associated Deaths. Am J Med 2000;108:518. PubMed
  10. Schneir AB, Ly BT, Clark RF. A case of withdrawal from the GHB precursors gamma-butyrolactone and 1,4-butanediol. J Emerg Med 2001;21:31-3.. PubMed
  11. Zvosec DL, Smith SW, McCutcheon JR, et al. Adverse events, including death, associated with the use of 1,4-butanediol. N Engl J Med. 2001;344:87-94.. PubMed
  12. Mason P, Kerns II W. Gamma Hydroxybutyric Acid (GHB) Intoxication. Acad Emerg Med 2002;9:730-39.. DOI
  13. Poldrugo, F., Barker, S., Basa, M., Mallardi, F., and Snead, O. C. Ethanol potentiates the toxic effects of 1,4-butanediol. Alcohol Clin.Exp.Res 1985;9(6):493-497. PubMed
  14. Thai, D., Dyer, J. E., Jacob, P., and Haller, C. A. Clinical pharmacology of 1,4-butanediol and gamma-hydroxybutyrate after oral 1,4-butanediol administration to healthy volunteers. Clin.Pharmacol Ther. 2007;81(2):178-184. PubMed
  15. Boscolo-Berto R, Viel G, Montagnese S, Raduazzo DI, Ferrara SD, Dauvilliers Y. Narcolepsy and effectiveness of gamma-hydroxybutyrate (GHB): a systematic review and meta-analysis of randomized controlled trials. Sleep Med Rev. 2012 Oct;16(5):431-43. 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 1,4-butanediol and Letrozole Together: Common Questions

Is it safe to take 1,4-butanediol with Letrozole?
We do not list a known interaction between 1,4-butanediol 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 1,4-butanediol and Letrozole have any of the same side effects?
Yes — our sources link each of them separately to one 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 1,4-butanediol and Letrozole combination checked?
Interactions in our licensed database are recorded against drug classes. Letrozole is filed under 4 classifications, and 1,4-butanediol has documented interactions with 10 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 1,4-butanediol interact with any other medications?
Yes. 1,4-butanediol has 271 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 — 1,4-butanediol 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

1,4-butanediol 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 1,4-butanediol?

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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.