Drug & supplement interaction

Quassia + Ivermectin

Ivermectin brand names: Stromectol, Mectizan, Sklice, Soolantra.

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 Quassia and Ivermectin 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 label for Ivermectin states a food rule worth keeping to, and 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

Quassia and Ivermectin

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 Ivermectin and Quassia 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.

Quassia safety at a glance

Quassia overall Use caution Likely fine in small amounts used in foods, but larger or long-term doses may irritate the digestive tract.
Pregnancy Likely Unsafe When used orally; avoid using. Quassia has cytotoxic and emetic properties. There is insufficient reliable information available about the safety of rectal or t... Read the full pregnancy detail
Breastfeeding Likely Unsafe When used orally; avoid using. Quassia has cytotoxic and emetic properties. There is insufficient reliable information available about the safety of rectal or t... 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 Ivermectin and Quassia? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
How we checked

Why No Interaction Is Listed for Ivermectin

Interactions in our licensed database are recorded against drug classes, not just single drug names. Ivermectin is filed under 4 classifications — including topical drugs, p-glycoprotein substrates, oral drugs. Quassia has documented interactions with 6 drug classes — the most serious being antidiabetes drugs (moderate), digoxin (lanoxin) (moderate) and diuretic drugs (moderate) — and none of Ivermectin’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

Quassia Does Interact With Other Medications

Quassia has 162 moderate, 36 minor known drug interactions in our database — Ivermectin isn’t one of them. If you take anything else, check it against the full list below.

Moderate 162 Minor 36 No known interaction 2,632 (incl. Ivermectin)
Taking anything else?

Check Another of Your Medications Against Quassia

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

What to actually watch for

No Interaction Found — But Data Suggests Quassia and Ivermectin 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. One of them is worth acting on rather than waiting out — marked below.

  • Loss of vision Worth acting on Additional detail

    Quassia

    “Orally, quassia can cause mucous membrane irritation, nausea, and vomiting when used in medicinal amounts (4,18). Long-term use can cause vision changes and blindness (18).

    Topically, quassia seems to be well tolerated. No adverse effects have been reported.”

    Quassia · Natural Medicines adverse-effect record, reported in nausea and vomiting.

    3 sources cited
    1. 4. Newall CA, Anderson LA, Philpson JD. Herbal Medicine: A Guide for Healthcare Professionals. London, UK: The Pharmaceutical Press, 1996.
    2. 18. Gruenwald J, Brendler T, Jaenicke C. PDR for Herbal Medicines. 1st ed. Montvale, NJ: Medical Economics Company, Inc., 1998.
    3. 99995. Ferrari A, Diehl C. Evaluation of the efficacy and tolerance of a topical gel with 4% quassia extract in the treatment of rosacea. J Clin Pharmacol. 2012;52(1):84-8. PubMed

    Ivermectin

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

  • Vomiting / Nausea Additional detail

    Quassia

    “Orally, quassia has been reported to cause mucous membrane irritation, nausea, and vomiting when used in medicinal amounts (4,18).”

    Quassia · Natural Medicines adverse-effect record, reported in nausea and vomiting.

    2 sources cited
    1. 4. Newall CA, Anderson LA, Philpson JD. Herbal Medicine: A Guide for Healthcare Professionals. London, UK: The Pharmaceutical Press, 1996.
    2. 18. Gruenwald J, Brendler T, Jaenicke C. PDR for Herbal Medicines. 1st ed. Montvale, NJ: Medical Economics Company, Inc., 1998.

    Ivermectin

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

Reported for Quassia but not commonly for Ivermectin: blurred vision.

Effects for Ivermectin come from the ADVERSE REACTIONS section of its FDA label; effects for Quassia come from the Natural Medicines adverse-effect record, quoted above. Where a percentage is shown, it is the share of 6,298 voluntary FDA FAERS reports for Ivermectin that mention that effect — a reporting proportion, not an incidence rate and not evidence the drug caused it. Wording is matched across sources by our own clinical vocabulary, so treat this as a prompt to pay attention, not a diagnosis.

Special populations

Quassia in Pregnancy & Breastfeeding

Pregnancy And Lactation Likely Unsafe

When used orally; avoid using. Quassia has cytotoxic and emetic properties. There is insufficient reliable information available about the safety of rectal or topical use during pregnancy or lactation; avoid using.

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

How to take them

Some Ivermectin Products Have a Food Rule — Quassia Should Not Break It

At least one FDA label for a product containing Ivermectin says to take it on an empty stomach. Most supplements — Quassia included — are taken with a meal, so the easy mistake is swallowing both together at breakfast. Where that rule applies, keep Ivermectin on its own and move Quassia to a meal later in the day.

This may not be true of your version. Food instructions belong to the product, not the ingredient: two Ivermectin products can carry different directions, and extended-release forms often differ from immediate-release ones. The label we read is quoted below — check the directions on your own box or bottle, or ask your pharmacist, for how to take the exact product you were given.

Patients should take tablets on an empty stomach with water.

From the Dosage and Administration section of the FDA label we read for Ivermectin — where that label names a specific product, the instruction is that product's. Read the label on DailyMed ›

A food rule is not an interaction — it is about how much of the medicine you absorb. The directions that came with your own product, and your pharmacist, outrank anything on this page.

Overlapping uses

What Ivermectin Is Prescribed For, and What Quassia Has Been Studied For

These two come up together because they touch the same health topic — not because they do the same job. Ivermectin is a prescription medicine with approved uses on its FDA label. Quassia is a supplement: what follows is what researchers have looked at it for, and how strong that evidence is.

Ivermectin is prescribed for: Ivermectin tablets (including Stromectol) are used to treat two parasitic infections: strongyloidiasis (a roundworm infection of the intestinal tract) and onchocerciasis (river blindness, caused by a parasitic worm spread by blackfly bites). These are prescription uses for serious infections. Topical ivermectin lotion — sold under several names including RID One and Done, Head Lice Treatment Ivermectin Lotion, Scalp Care Lotions, and others — is applied to the scalp to treat head lice. A separate topical ivermectin cream (1%), available as Soolantra and ivermectin cream 1%, is used to treat the inflammatory pimple-like bumps of rosacea.

Quassia has been studied for:

  • Rosacea studied, not established Quassia has been studied for this. Natural Medicines rates the evidence: Insufficient Reliable Evidence To Rate Read what the research shows

    Quassia for rosacea

    Preliminary clinical research in patients with rosacea shows that applying quassia 4% gel twice daily for 45 days reduces flushing, redness, and telangiectasia by approximately 74%, 56%, and 50%, respectively, compared with baseline. A moderate to complete overall improvement occurred in 89% of patients. The validity of these results is limited by a lack of control group.

    1 source cited
    1. 99995. Ferrari A, Diehl C. Evaluation of the efficacy and tolerance of a topical gel with 4% quassia extract in the treatment of rosacea. J Clin Pharmacol. 2012;52(1):84-8. PubMed

Effectiveness ratings and the research summaries above are the verbatim record from the Natural Medicines database, which grades evidence from “Effective” down to “Insufficient Reliable Evidence To Rate”. A rating below the top of that scale means researchers have looked at it — not that it works, and never that it can stand in for a prescribed medicine. Do not stop or replace Ivermectin on your own; if you are taking Quassia for the same health topic, tell your prescriber, especially if the medicine is being adjusted to a target.

From our Q&A

Questions About Quassia or Ivermectin

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

This page covers Quassia only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Ivermectin page lists 58 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), St. John's Wort (major), Sweet Orange (major), Bitter Melon (moderate) and Black Pepper (moderate).

By severity: 3 major · 37 moderate · 18 minor.

Open the Ivermectin interaction page

One more smart check

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

We hold 172 real supplement products containing Quassia, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Quassia. Even though Quassia itself has no known interaction with Ivermectin, 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 Quassia and Ivermectin 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 Quassia
Top half

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

29 days ago today
Medication Ivermectin
Top 1%

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

What is Quassia?

  • Loss of appetite
  • Digestive upset
  • Head lice (topical)
  • Intestinal worms/parasites
  • Bitter tonic

Quassia is a tropical wood known for its very bitter taste, traditionally used as a digestive bitter and as a folk remedy for parasites and head lice. Human evidence for these uses is limited, and high doses may irritate the stomach, so it should be used cautiously and avoided in pregnancy.

Quassia amara · Simaroubaceae · Wood (bark and stem wood) · Dried wood chips, tea/infusion, liquid extract, tincture, capsules, and topical lotions

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

Quassia: dosing

There is no well-established, standardized dose for quassia. Traditional preparations include a bitter tea made from a small amount of wood chips, as well as tinctures and capsules.Because the strength of products varies and reliable dosing studies are lacking, follow the directions on the product label and use the lowest amount that works. Avoid large or long-term doses.

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

Read the full Quassia monograph & all interactions
Medication

About Ivermectin

What Is Ivermectin Used For?

Brand names: Stromectol, Mectizan, Sklice, Soolantra

Ivermectin tablets (including Stromectol) are used to treat two parasitic infections: strongyloidiasis (a roundworm infection of the intestinal tract) and onchocerciasis (river blindness, caused by a parasitic worm spread by blackfly bites). These are prescription uses for serious infections.

Topical ivermectin lotion — sold under several names including RID One and Done, Head Lice Treatment Ivermectin Lotion, Scalp Care Lotions, and others — is applied to the scalp to treat head lice. A separate topical ivermectin cream (1%), available as Soolantra and ivermectin cream 1%, is used to treat the inflammatory pimple-like bumps of rosacea.

Most-Reported Side Effects for Ivermectin

From FAERS, the FDA’s public side-effect reporting system (6,298 reports, all brands). Reports are voluntary and are not proof the drug caused the effect.

Headache 647 reports
Asthenia 590 reports
Fever 485 reports
Pruritus 388 reports
Diarrhea 292 reports
See full Ivermectin drug information
Keep checking

Other Drugs & Quassia

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

0Major
162Moderate
36Minor
2,631No known interaction
162 Moderate 36 Minor 2,631 No interaction
Moderate

162 interactions

Showing 60 of 162 moderate interactions — see all 162 on the Quassia page.

Minor

36 interactions

No interaction 2,631 drugs checked — show the list

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

Showing the 60 most looked-up of 2,631 medications checked with no known interaction — see the full Quassia list.

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

Quassia References

The 8 references that drive our Quassia 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. Newall CA, Anderson LA, Philpson JD. Herbal Medicine: A Guide for Healthcare Professionals. London, UK: The Pharmaceutical Press, 1996.
  2. Robbers JE, Speedie MK, Tyler VE. Pharmacognosy and Pharmacobiotechnology. Baltimore, MD: Williams & Wilkins, 1996.
  3. Gruenwald J, Brendler T, Jaenicke C. PDR for Herbal Medicines. 1st ed. Montvale, NJ: Medical Economics Company, Inc., 1998.
  4. Brinker F. Herb Contraindications and Drug Interactions. 2nd ed. Sandy, OR: Eclectic Medical Publications, 1998.
  5. Jensen O, Nielsen AO, Bjerregaard P. Pediculosis capitis treated with quassia tincture. Acta Derm Venereol 1978;58:557-9. DOI
  6. Diehl C, Ferrari A. Efficacy of topical 4% Quassia amara gel in facial seborrheic dermatitis:a randomized, double-blind, comparative study. J Drugs Dermatol. 2013;12(3):312-5.
  7. Ferrari A, Diehl C. Evaluation of the efficacy and tolerance of a topical gel with 4% quassia extract in the treatment of rosacea. J Clin Pharmacol. 2012;52(1):84-8. PubMed
  8. Husain GM, Singh PN, Singh RK, Kumar V. Antidiabetic activity of standardized extract of Quassia amara in nicotinamide-streptozotocin-induced diabetic rats. Phytother Res. 2011;25(12):1806-12.

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 Quassia and Ivermectin Together: Common Questions

Is it safe to take Quassia with Ivermectin?
We do not list a known interaction between Quassia and Ivermectin. 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 Quassia and Ivermectin have any of the same side effects?
Yes — our sources link each of them separately to 3 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.
Should I take Quassia and Ivermectin at the same time of day?
At least one FDA label for a product containing Ivermectin says to take it on an empty stomach, and supplements are usually taken with a meal — so taking them together at breakfast is the easy mistake. Where that applies, keep Ivermectin on its own and move Quassia to a meal later in the day. Food instructions belong to the product rather than the ingredient, so check the directions on your own box. This is about absorption, not an interaction.
Are Quassia and Ivermectin used for the same thing?
They overlap in purpose, which usually means the real question is whether you need both rather than whether they are safe together. This page lists the shared uses and how strong the evidence is for Quassia in each. That is a conversation for your prescriber, especially if Ivermectin is being adjusted to a target.
How was the Quassia and Ivermectin combination checked?
Interactions in our licensed database are recorded against drug classes. Ivermectin is filed under 4 classifications, and Quassia has documented interactions with 6 drug classes — none of Ivermectin'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 Quassia interact with any other medications?
Yes. Quassia has 198 documented drug interactions in our database — Ivermectin 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 Ivermectin interact with any supplements?
Yes. Ivermectin has documented interactions with 58 supplements in our database — Quassia is not one of them. The Ivermectin 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

Quassia monograph Uses, safety profile, and every drug interaction in one place Ivermectin drug information The full plain-English guide to this medication Ivermectin supplement interactions Every supplement checked against Ivermectin, 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 8 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Ivermectin and Quassia?

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.