Herb & supplement monograph

Pennyroyal Drug Interactions, Uses, Effectiveness, Safety & More

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS ·Updated July 2026

What is this page for?

First and foremost: how Pennyroyal interacts with medications. The heart of this page is the interaction list — every drug Pennyroyal is known to interact with, and how serious each one is.

But these pages have grown well beyond that into a full monograph — what Pennyroyal is, what people use it for and how strong the evidence is, its safety and side effects, and answers to the questions we’re asked most — written and reviewed by the clinical staff at HelloPharmacist. It’s educational information from our licensed clinical databases, not medical advice, and we don’t sell or endorse products. Our editorial policy

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Pennyroyal Drug Interactions: The Bottom Line

From the HelloPharmacist Editorial Team · Updated July 2026

Based on the available evidence, Pennyroyal drug interactions carry a moderate level of risk, driven mainly by this herb's known potential to harm the liver. None of the listed interactions are rated major, but none are minor either; all sit in the moderate range, and most are not well documented in human studies.

Interactions deserving the most attention

The combination that stands out is pennyroyal with acetaminophen (Tylenol). Pennyroyal can be toxic to the liver and uses up a protective substance the liver also relies on to safely clear acetaminophen. One case report describes liver failure in a woman who took both together. The evidence is limited, but because the possible harm is serious, this pairing deserves real caution, including with combination products that contain acetaminophen.

What the rest of the list means

Pennyroyal is listed alongside several dozen medications, but a long list does not mean every combination has been shown to cause harm. Most of these interactions rest on limited or theoretical evidence rather than well-controlled human studies. The consistent moderate rating largely reflects sensible caution about pennyroyal's effects on the liver rather than proven problems with each individual medication.

Check your medications against Pennyroyal

Based on HelloPharmacist’s Pennyroyal interaction data and reviewed under our editorial standards.

Interaction report

Drugs that interact with Pennyroyal

69 medications have a known interaction with Pennyroyal, graded by severity. Select any drug for the full evidence-based detail.

Don’t want to scroll the list? Just ask.

Tell us the medications you take and we’ll check each one against Pennyroyal using our pharmacist-reviewed interaction data.

AI summaries are generated from our Pennyroyal interaction data for education only — always confirm with your pharmacist. How we use AI

2,830 drugs

Read The List Like a Pharmacist

What Severity, Likelihood & Evidence Mean

Severity — How Serious It Can Be

Major. Clinically significant; generally best avoided, or used only under direct professional supervision.
Moderate. May need monitoring, a dose adjustment, or separating the times you take each one.
Minor. Generally not clinically significant, but still worth noting and mentioning to your pharmacist.
No known interaction. Checked against our sources with nothing documented — not the same as proven safety.

Likelihood — How Well It’s Documented

Likely. Well-controlled human studies have demonstrated the likely existence of this interaction
Probable. Interaction 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.
Possible. 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
Unlikely. Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans.

Where This Data Comes From

Interaction records are evidence-graded and sourced from the Natural Medicines database (TRC Healthcare), the same reference used by pharmacists and hospitals.
Each drug listed above links to the full report for that exact Pennyroyal combination — clinical detail, likelihood, evidence level, and citations.
Content is reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

The big picture

The kinds of drugs Pennyroyal affects

Every type of medication (drug category) Pennyroyal is known to interact with. Open any category for the detail — or search your exact drug in the checker above.

All 1 drug category Pennyroyal interacts with

Acetaminophen (tylenol, Others)

Acetaminophen (Tylenol, Others)

Concomitant use of pennyroyal essential oil and acetaminophen might increase the risk of acetaminophen-induced hepatotoxicity.
Pennyroyal is hepatotoxic and depletes hepatic glutathione levels in a similar manner to acetaminophen. A case report describes hepatic failure in a female who took pennyroyal and acetaminophen concurrently.

Likelihood Possible Evidence D

Monograph

Pennyroyal: Uses, Safety & Side Effects

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS · Reviewed July 2026 ·

The bottom line

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.

Scientific name: Mentha pulegium
Family: Lamiaceae
Part used: Leaves, flowering tops, and essential oil
Common forms: Tea, dried herb, tincture, essential oil

People commonly use it for

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

Popular and traditional uses — not proof it works. See “Uses & effectiveness” below for the evidence.

Safety at a glance

OverallBest avoided

Pennyroyal oil is highly toxic and has caused liver failure and death.

PregnancyLikely Unsafe

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

Read the full pregnancy detail

BreastfeedingLikely Unsafe

When used orally or topically; avoid using.

Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center). Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

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Overview

Pennyroyal (Mentha pulegium) is a small, strongly scented plant in the mint family. It grows in Europe, parts of Asia, and North America, often in damp soils. It has a smell similar to spearmint or peppermint.

People have used pennyroyal for centuries as a folk remedy, made into a tea or used as an essential oil. Traditionally it was used for digestion, colds, menstrual problems, and as an insect repellent. The concentrated essential oil is far more dangerous than the dried herb, but both carry real risk.

How it works

The main compound in pennyroyal oil is pulegone, along with a related substance called menthofuran. When the body breaks down pulegone, it forms toxic byproducts that can damage the liver and other organs.

These chemicals are thought to be behind both the plant's traditional effects and its serious toxicity. Most of what is known comes from laboratory and animal research and from human poisoning cases, not from controlled studies showing safe benefits.

Effectiveness

Does Pennyroyal work?

Here’s what the research actually shows for each use — graded by Natural Medicines and reviewed by Dr. Brian Staiger, PharmD.

Evidence overview · 8 uses evaluated

8 Insufficient evidence

How to read these evidence grades

Natural Medicines’ 7-point scale. We show each rating’s label word-for-word.

1EffectiveStrong, consistent evidence it works.

2Likely EffectiveGood evidence, though not yet conclusive.

3Possibly EffectiveSome evidence suggests a benefit.

4Possibly IneffectiveSome evidence it may not help.

5Likely IneffectiveFairly strong evidence it doesn’t help.

6IneffectiveStrong evidence it doesn’t work.

7Insufficient Reliable Evidence to RateToo little research to say either way.

For Pennyroyal, current evidence isn’t strong enough to rate any specific use. The conditions it has been studied for are listed below.

Also studied for 8 conditions — evidence insufficient to rate

Insufficient Reliable Evidence To Rate Abortion