Drug & supplement interaction

Pennyroyal + Trimethoprim

Trimethoprim brand names: Proloprim, Trimpex.

No Known Interaction
Medically reviewed by · Updated July 2026 · Pair last verified Sep 20, 2026
The bottom line No known interaction

We found no known interaction between Pennyroyal and Trimethoprim 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

Pennyroyal and Trimethoprim

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 Trimethoprim and Pennyroyal 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.

Pennyroyal safety at a glance

Pennyroyal overall Avoid Pennyroyal oil is highly toxic and has caused liver failure and death.
Pregnancy Likely Unsafe When used orally or topically. Pennyroyal essential oil has been used traditionally as an abortifacient. Pennyroyal leaf tea is reported to cause onset of mense... Read the full pregnancy detail
Breastfeeding Likely Unsafe When used orally or topically; avoid using. 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 Trimethoprim and Pennyroyal? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
How we checked

Why No Interaction Is Listed for Trimethoprim

Interactions in our licensed database are recorded against drug classes, not just single drug names. Trimethoprim is filed under 4 classifications — including qt interval-prolonging drugs, antibiotic drugs, oral drugs. Pennyroyal has documented interactions with 1 drug class — the most serious being acetaminophen (tylenol, others) (moderate) — and none of Trimethoprim’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

Pennyroyal Does Interact With Other Medications

Pennyroyal has 69 moderate known drug interactions in our database — Trimethoprim isn’t one of them. If you take anything else, check it against the full list below.

Moderate 69 No known interaction 2,761 (incl. Trimethoprim)
Taking anything else?

Check Another of Your Medications Against Pennyroyal

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

What to actually watch for

No Interaction Found — But Data Suggests Pennyroyal and Trimethoprim 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.

  • A skin rash reported in 5.3% of FDA reports for Trimethoprim Additional detail

    Pennyroyal

    “Topically, pennyroyal essential oil can cause urticarial rashes and dermatitis (6,5601).”

    Pennyroyal · Natural Medicines adverse-effect record, reported in dermatitis.

    2 sources cited
    1. 6. The Review of Natural Products by Facts and Comparisons. St. Louis, MO: Wolters Kluwer Co., 1999.
    2. 5601. Sullivan JB Jr, Rumack BH, Thomas H Jr, et al. Pennyroyal oil poisoning and hepatotoxicity. JAMA 1979;242:2873-4. DOI

    Trimethoprim

    Listed in the ADVERSE REACTIONS section of the FDA label for Trimethoprim, and in voluntary FDA adverse-event reports. Read the label on DailyMed ›

  • Nausea reported in 6.0% of FDA reports for Trimethoprim Additional detail

    Pennyroyal

    “Orally, herbal teas prepared with pennyroyal leaves can cause nausea and abdominal cramping (12). Pennyroyal essential oil causes more severe gastrointestinal effects, including abdominal pain, burning of the throat, and vomiting (12,5601).”

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

    2 sources cited
    1. 12. McGuffin M, Hobbs C, Upton R, Goldberg A, eds. American Herbal Products Association's Botanical Safety Handbook. Boca Raton, FL: CRC Press, LLC 1997.
    2. 5601. Sullivan JB Jr, Rumack BH, Thomas H Jr, et al. Pennyroyal oil poisoning and hepatotoxicity. JAMA 1979;242:2873-4. DOI

    Trimethoprim

    Listed in the ADVERSE REACTIONS section of the FDA label for Trimethoprim, and in voluntary FDA adverse-event reports. Read the label on DailyMed ›

  • Vomiting Additional detail

    Pennyroyal

    Recorded for Pennyroyal in the same Natural Medicines adverse-effect record shown under Nausea above.

    Trimethoprim

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

Reported for Pennyroyal but not commonly for Trimethoprim: hallucinations, an irregular heartbeat, stomach pain and kidney problems.

Effects for Trimethoprim come from the ADVERSE REACTIONS section of its FDA label; effects for Pennyroyal come from the Natural Medicines adverse-effect record, quoted above. Where a percentage is shown, it is the share of 93,588 voluntary FDA FAERS reports for Trimethoprim 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

Pennyroyal in Pregnancy & Breastfeeding

Pregnancy Likely Unsafe

When used orally or topically. Pennyroyal essential oil has been used traditionally as an abortifacient. Pennyroyal leaf tea is reported to cause onset of menses.

Lactation Likely Unsafe

When used orally or topically; 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

Overlapping uses

What Trimethoprim Is Prescribed For, and What Pennyroyal Has Been Studied For

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

Trimethoprim is prescribed for: Trimethoprim tablets are used to treat initial episodes of uncomplicated urinary tract infections (UTIs). It works against specific bacteria — including E. coli, Proteus mirabilis, Klebsiella pneumoniae, Enterobacter species, and coagulase-negative Staphylococcus species (including S. saprophyticus).

Read the rest of what Trimethoprim is prescribed for

It should only be used when there is a proven or strongly suspected bacterial infection. Your doctor may order a urine culture to confirm which bacteria are present and whether trimethoprim will work against them.

Pennyroyal has been studied for:

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

    Pennyroyal for pneumonia

    Although there has been interest in using oral pennyroyal for treating pneumonia, there is insufficient reliable information about the clinical effects of pennyroyal for this purpose.

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 Trimethoprim on your own; if you are taking Pennyroyal for the same health topic, tell your prescriber, especially if the medicine is being adjusted to a target.

From our Q&A

Questions About Pennyroyal or Trimethoprim

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

This page covers Pennyroyal only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Trimethoprim page lists 59 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: 7 major · 41 moderate · 11 minor.

From our pharmacist’s overview on the Trimethoprim page

“Most prescriptions for trimethoprim are short courses for bladder infections, which makes it easy to assume nothing swallowed alongside it matters much. Seven of the 59 supplement and herbal ingredients here rate major, though, and nearly all of them involve heart rhythm: grapefruit in large amounts, ephedra, and a few others can prolo…”

Reviewed by 2 · Jul 18, 2026

Open the Trimethoprim interaction page

One more smart check

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

We hold 11 real supplement products containing Pennyroyal, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Pennyroyal. Even though Pennyroyal itself has no known interaction with Trimethoprim, 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 Pennyroyal and Trimethoprim 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 Pennyroyal
Steady interest

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

29 days ago today
Medication Trimethoprim
Steady interest

#2,254 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 Pennyroyal reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 20, 2026. The Pennyroyal and Trimethoprim records this page draws on were last updated July 11, 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 Pennyroyal

What is Pennyroyal?

  • Digestive upset
  • Menstrual cramps
  • Inducing menstruation or abortion (dangerous)
  • Colds and coughs
  • Insect repellent

Pennyroyal is a mint-family plant whose essential oil is highly toxic and has caused serious poisonings and deaths, especially when used to try to bring on a period or end a pregnancy. There is no reliable evidence that it safely treats any condition, and the oil should never be swallowed. Avoid pennyroyal and talk to your pharmacist or doctor about safer options.

Mentha pulegium · Lamiaceae · Leaves, flowering tops, and essential oil · Tea, dried herb, tincture, essential oil

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

Pennyroyal: dosing

There is no established safe dose for pennyroyal, and health experts generally advise against using it at all because of its toxicity.The essential oil should never be swallowed, and even teas made from the herb carry risk. Because of these dangers, we do not recommend a dose.

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

Read the full Pennyroyal monograph & all interactions
Medication

About Trimethoprim

What Is Trimethoprim Used For?

Brand names: Proloprim, Trimpex

Trimethoprim tablets are used to treat initial episodes of uncomplicated urinary tract infections (UTIs). It works against specific bacteria — including E. coli, Proteus mirabilis, Klebsiella pneumoniae, Enterobacter species, and coagulase-negative Staphylococcus species (including S. saprophyticus).

It should only be used when there is a proven or strongly suspected bacterial infection. Your doctor may order a urine culture to confirm which bacteria are present and whether trimethoprim will work against them.

Most-Reported Side Effects for Trimethoprim

From FAERS, the FDA’s public side-effect reporting system (95,001 reports, all brands). Reports are voluntary and are not proof the drug caused the effect.

Fever 6,904 reports
Fatigue 5,992 reports
Diarrhea 5,716 reports
Nausea 5,685 reports
Dyspnea 5,098 reports
See full Trimethoprim drug information
Keep checking

Other Drugs & Pennyroyal

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

0Major
69Moderate
0Minor
2,760No known interaction
69 Moderate 2,760 No interaction
Moderate

69 interactions

Showing 60 of 69 moderate interactions — see all 69 on the Pennyroyal page.

No interaction 2,760 drugs checked — show the list

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

Showing the 60 most looked-up of 2,760 medications checked with no known interaction — see the full Pennyroyal list.

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

Pennyroyal References

The 8 references that drive our Pennyroyal 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. The Review of Natural Products by Facts and Comparisons. St. Louis, MO: Wolters Kluwer Co., 1999.
  3. McGuffin M, Hobbs C, Upton R, Goldberg A, eds. American Herbal Products Association's Botanical Safety Handbook. Boca Raton, FL: CRC Press, LLC 1997.
  4. Bakerink JA, Gospe SM Jr, Dimand RJ, Eldridge MW. Multiple organ failure after ingestion of pennyroyal oil from herbal tea in two infants. Pediatrics 1996;98:944-7. DOI
  5. Sudekum M, Poppenga RH, Raju N, Braselton WE Jr. Pennyroyal oil toxicosis in a dog. J Am Vet Med Assoc 1992;200:817-8.. DOI
  6. Anderson IB, Mullen WH, Meeker JE, et al. Pennyroyal toxicity: measurement of toxic metabolite levels in two cases and review of the literature. Ann Intern Med 1996;124:726-34. PubMed
  7. Sullivan JB Jr, Rumack BH, Thomas H Jr, et al. Pennyroyal oil poisoning and hepatotoxicity. JAMA 1979;242:2873-4. DOI
  8. Fozard J, Hieger M. Hepatic failure from pennyroyal tea interaction with medications metabolized by the cytochrome P450 enzymes. Am J Ther 2019 Aug 13. doi: 10.1097/MJT.0000000000001052. [Epub ahead of print]. 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 Pennyroyal and Trimethoprim Together: Common Questions

Is it safe to take Pennyroyal with Trimethoprim?
We do not list a known interaction between Pennyroyal and Trimethoprim. 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 Pennyroyal and Trimethoprim 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.
Are Pennyroyal and Trimethoprim 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 Pennyroyal in each. That is a conversation for your prescriber, especially if Trimethoprim is being adjusted to a target.
How was the Pennyroyal and Trimethoprim combination checked?
Interactions in our licensed database are recorded against drug classes. Trimethoprim is filed under 4 classifications, and Pennyroyal has documented interactions with 1 drug class — none of Trimethoprim'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 Pennyroyal interact with any other medications?
Yes. Pennyroyal has 69 documented drug interactions in our database — Trimethoprim 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 Trimethoprim interact with any supplements?
Yes. Trimethoprim has documented interactions with 59 supplements in our database — Pennyroyal is not one of them. The Trimethoprim 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

Pennyroyal monograph Uses, safety profile, and every drug interaction in one place Trimethoprim drug information The full plain-English guide to this medication Trimethoprim supplement interactions Every supplement checked against Trimethoprim, 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 Trimethoprim and Pennyroyal?

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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.