Drug & supplement interaction

Coltsfoot + Efavirenz

Efavirenz brand name: Sustiva.

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

Coltsfoot has a moderate interaction with Efavirenz. Hepatotoxic pyrrolizidine alkaloids (PA) are substrates of cytochrome P450 3A4 (CYP3A4).

Read the full interaction report
SeverityModerate
LikelihoodPossible
EvidenceD
What do Severity, Likelihood & Evidence mean?
Know someone taking this? Share
Facebook Post Reddit Email
On this page
Interaction report

Coltsfoot and Efavirenz

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

Moderate

CYTOCHROME P450 3A4 (CYP3A4) INDUCERS

Why this applies to Efavirenz

Efavirenz falls under CYTOCHROME P450 3A4 (CYP3A4) INDUCERS — the group Coltsfoot interacts with.

Hepatotoxic pyrrolizidine alkaloids (PA) are substrates of cytochrome P450 3A4 (CYP3A4). Theoretically, drugs that induce CYP3A4 might increase the conversion of PAs to toxic metabolites. Some drugs that induce CYP3A4 include carbamazepine (Tegretol), phenobarbital, phenytoin (Dilantin), rifampin, rifabutin (Mycobutin), and 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 concern with pairing coltsfoot and efavirenz. The worry isn't about your HIV medicine getting weaker or stronger. It's the other way around. Coltsfoot can contain pyrrolizidine alkaloids, plant compounds that are hard on the liver. These compounds get turned into their toxic forms by a liver enzyme called CYP3A4, and efavirenz happens to speed that enzyme up. So in theory, taking them together could ramp up the production of liver-damaging byproducts from the coltsfoot.

I want to be honest that this is based on lab and animal research, not real human cases, so the actual risk is uncertain. Still, given coltsfoot's liver concerns, I'd skip it unless you've talked it over with your doctor or pharmacist first.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Chojkier M. Hepatic sinusoidal-obstruction syndrome: toxicity of pyrrolizidine alkaloids. J Hepatol 2003;39:437-46. PubMed
  2. 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

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

Coltsfoot Also Interacts With Other Medications

Coltsfoot has 373 moderate known drug interactions in our database — the Efavirenz one above is one of them. If you take anything else, check it against the full list below.

Moderate 373 No known interaction 2,457 (incl. Efavirenz)
Taking anything else?

Check Another of Your Medications Against Coltsfoot

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

Everything else you take

See Every Supplement That Interacts With Efavirenz

This page covers Coltsfoot only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Efavirenz page lists 159 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), Acacia Rigidula (moderate) and Adrafinil (moderate).

By severity: 3 major · 117 moderate · 39 minor.

From our pharmacist’s overview on the Efavirenz page

“Efavirenz (Sustiva) is an HIV medicine, so an interaction that weakens it can cost more than a bad day; it can invite viral resistance. That makes this a list to treat with genuine care.”

Reviewed by 2 · Jul 18, 2026

Open the Efavirenz interaction page

One more smart check

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

We hold 60 real supplement products containing Coltsfoot, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Coltsfoot. Your product may carry other ingredients that interact with Efavirenz too, on top of Coltsfoot — 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 Coltsfoot and Efavirenz 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 Coltsfoot
Steady interest

#1,050 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Efavirenz
Steady interest

#1,574 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 Coltsfoot

What is Coltsfoot?

Coltsfoot
  • Cough
  • Sore throat
  • Bronchitis and congestion
  • Loosening mucus (expectorant)
  • Asthma symptoms

Coltsfoot is a traditional herb long used to soothe coughs and clear mucus, but solid human evidence for these uses is lacking. More importantly, the raw plant can contain liver-toxic pyrrolizidine alkaloids, so it carries real safety concerns and is best avoided unless you use a product certified to be free of these compounds.

Read the full Coltsfoot monograph & all interactions
Medication

About Efavirenz

What Is Efavirenz Used For?

Brand name: Sustiva

Efavirenz is used to treat HIV-1 (human immunodeficiency virus type 1) infection. It is always used together with other antiretroviral medicines — never on its own.

It is approved for adults and for children who are at least 3 months old and weigh at least 3.5 kg (about 7.7 lbs). Both the capsule and tablet forms are approved for this use.

See full Efavirenz drug information
Keep checking

Other Drugs & Coltsfoot

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

0Major
373Moderate
0Minor
2,456No known interaction
373 Moderate 2,456 No interaction
Moderate

373 interactions

Showing 60 of 373 moderate interactions — see all 373 on the Coltsfoot page.

No interaction 2,456 drugs checked — show the list

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

Showing the 60 most looked-up of 2,456 medications checked with no known interaction — see the full Coltsfoot list.

See the full Coltsfoot interactions page
See every supplement checked against Efavirenz, 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
Coltsfoot monograph › Uses, safety, and every drug interaction in one place Efavirenz supplement interactions › Every supplement checked against Efavirenz, ranked by severity Efavirenz 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 Coltsfoot and Efavirenz Together: Common Questions

Can you take Coltsfoot with Efavirenz?
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 Coltsfoot and Efavirenz 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 Efavirenz and Coltsfoot?

Our pharmacists answer your medication & supplement questions — free.

Ask a pharmacist

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.