Drug & supplement interaction

Ergot + Letrozole, Ribociclib Succinate

Letrozole, Ribociclib Succinate brand name: Kisqali Femara Co-Pack.

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

Ergot has a moderate interaction with Letrozole, Ribociclib Succinate. Ergotamine, a constituent of ergot, is a substrate of cytochrome P450 3A4 (CYP3A4).

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

Ergot and Letrozole, Ribociclib Succinate

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

Moderate

CYTOCHROME P450 3A4 (CYP3A4) INHIBITORS

Why this applies to Letrozole, Ribociclib Succinate

Letrozole, Ribociclib Succinate falls under CYTOCHROME P450 3A4 (CYP3A4) INHIBITORS — the group Ergot interacts with.

Ergotamine, a constituent of ergot, is a substrate of cytochrome P450 3A4 (CYP3A4). Theoretically, drugs that inhibit CYP3A4 might increase the risk of ergot toxicity. Some of these drugs include amiodarone (Cordarone), clarithromycin (Biaxin), diltiazem (Cardizem), erythromycin (E-mycin, Erythrocin), indinavir (Crixivan), ritonavir (Norvir), saquinavir (Fortovase, Invirase), and many others.
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 know about your Kisqali plus Femara combo: the ribociclib part is a fairly strong blocker of a liver enzyme called CYP3A4. That same enzyme is what your body uses to break down ergot's active chemicals (ergot alkaloids like ergotamine). So if you took ergot alongside this regimen, your body would clear those ergot chemicals more slowly, letting them build up.

That matters because ergot at higher levels can squeeze blood vessels too hard, causing cold or numb hands and feet, leg cramps, or worse. This concern is mostly theoretical and based on weak, anecdotal reports, but ergot itself is genuinely unsafe as a home remedy. Please don't use it, and check with your oncology pharmacist about anything you're taking.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Eadie MJ. Convulsive ergotism: epidemics of the serotonin syndrome? Lancet Neurol 2003;2:429-34. 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

Ergot Also Interacts With Other Medications

Ergot has 461 moderate known drug interactions in our database — the Letrozole, Ribociclib Succinate one above is one of them. If you take anything else, check it against the full list below.

Moderate 461 No known interaction 2,369 (incl. Letrozole, Ribociclib Succinate)
Taking anything else?

Check Another of Your Medications Against Ergot

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

Everything else you take

See Every Supplement That Interacts With Letrozole, Ribociclib Succinate

This page covers Ergot only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Letrozole, Ribociclib Succinate page lists 155 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), American Hellebore (major), Arsenic (major), Cesium (major) and Ephedra (major).

By severity: 8 major · 109 moderate · 38 minor.

From our pharmacist’s overview on the Letrozole, Ribociclib Succinate page

“Grapefruit tops my worry list for anyone taking the Kisqali Femara Co-Pack (letrozole and ribociclib), because it blocks the enzyme, CYP3A4, that clears ribociclib and can push levels of this breast cancer drug higher than intended. That enzyme thread runs through 121 of the 155 ingredients on this page, and with eight rated major, rea…”

Reviewed by 2 · Jul 18, 2026

Open the Letrozole, Ribociclib Succinate interaction page

How much people look this up

Where Ergot and Letrozole, Ribociclib Succinate 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 Ergot
Top half

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

29 days ago today
Medication Letrozole, Ribociclib Succinate
Steady interest

#1,514 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 Ergot

What is Ergot?

Ergot
  • Heavy menstrual or uterine bleeding
  • Bleeding after childbirth
  • Migraine headaches
  • Stimulating uterine contractions

Ergot is a toxic fungus that grows on rye and contains powerful chemicals (ergot alkaloids) that strongly narrow blood vessels and squeeze the uterus. Because raw ergot is poisonous and the dose is impossible to control safely, it should never be used as a home remedy or supplement. Some purified ergot chemicals are used as prescription drugs under strict medical supervision, but the crude herb is not safe to take.

Read the full Ergot monograph & all interactions
Keep checking

Other Drugs & Ergot

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

0Major
461Moderate
0Minor
2,368No known interaction
461 Moderate 2,368 No interaction
Moderate

461 interactions

Showing 60 of 461 moderate interactions — see all 461 on the Ergot page.

No interaction 2,368 drugs checked — show the list

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

Showing the 60 most looked-up of 2,368 medications checked with no known interaction — see the full Ergot list.

See the full Ergot interactions page
See every supplement checked against Letrozole, Ribociclib Succinate, 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
Ergot monograph › Uses, safety, and every drug interaction in one place Letrozole, Ribociclib Succinate supplement interactions › Every supplement checked against Letrozole, Ribociclib Succinate, 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 Ergot and Letrozole, Ribociclib Succinate Together: Common Questions

Can you take Ergot with Letrozole, Ribociclib Succinate?
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 Ergot and Letrozole, Ribociclib Succinate 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 Letrozole, Ribociclib Succinate and Ergot?

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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.