Drug & supplement interaction

Fennel + Acetaminophen

Acetaminophen brand names: Tylenol Ex Strength, Children's Tylenol, Tylenol, Children's Tylenol Meltaways.

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 Fennel and Acetaminophen 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

Fennel and Acetaminophen

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 Acetaminophen and Fennel 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.

Fennel safety at a glance

Fennel overall Use caution Generally safe as a food, but concentrated supplements and essential oil need more caution.
Pregnancy Possibly Unsafe When used orally. Observational research has found that regular use of fennel during pregnancy is associated with shortened gestation. Read the full pregnancy detail
Breastfeeding Possibly Unsafe When used orally. Case reports have linked consumption of an herbal tea containing extracts of fennel, licorice, anise, and goat's rue to neurotoxicity in two b... 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 Acetaminophen and Fennel? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
How we checked

Why No Interaction Is Listed for Acetaminophen

Interactions in our licensed database are recorded against drug classes, not just single drug names. Acetaminophen is filed under 8 classifications — including cytochrome p450 2e1 (cyp2e1) substrates, glucuronidated drugs, cytochrome p450 1a2 (cyp1a2) substrates. Fennel has documented interactions with 6 drug classes — the most serious being anticoagulant/antiplatelet drugs (moderate), ciprofloxacin (cipro) (moderate) and contraceptive drugs (moderate) — and none of Acetaminophen’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

Fennel Does Interact With Other Medications

Fennel has 740 moderate known drug interactions in our database — Acetaminophen isn’t one of them. If you take anything else, check it against the full list below.

Moderate 740 No known interaction 2,090 (incl. Acetaminophen)
Taking anything else?

Check Another of Your Medications Against Fennel

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

What to actually watch for

No Interaction Found — But Data Suggests Fennel and Acetaminophen 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. 3 of them are worth acting on rather than waiting out — marked below.

  • Wheezing Worth acting on Additional detail

    Fennel

    “A case report describes an 11-year-old male who developed an allergy to fennel-containing toothpaste. Immediately after using the toothpaste, the patient experienced sneezing, coughing, itchy mouth, rhinorrhea, nasal congestion, wheezing, difficulty breathing, and palpitations, which resolved within 10 minutes of spitting out the toothpaste and rinsing the mouth.”

    Fennel · Natural Medicines adverse-effect record, reported in allergic rhinitis (hay fever).

    1 source cited
    1. 103822. Denaxa D, Arkwright PD. Fennel as a cause of immediate hypersensitivity to toothpaste. Ann Allergy Asthma Immunol. 2020;125(1):99-100. PubMed

    “Orally, fennel and fennel seed have been reported to cause bronchial asthma.”

    Fennel · Natural Medicines adverse-effect record, reported in asthma.

    1 source cited
    1. 49478. LEVY, S. B. Bronchial asthma due to ingestion of fennel and fennel seed. Ann.Allergy 1948;6(4):415.

    Acetaminophen

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

  • Shortness of breath Worth acting on Additional detail

    Fennel

    Recorded for Fennel in the same Natural Medicines adverse-effect record shown under Wheezing above.

    Acetaminophen

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

  • An allergic reaction Worth acting on Additional detail

    Fennel

    “Advise patients to avoid excessive sunlight or ultraviolet light exposure while using fennel (19). Allergic reactions affecting the skin such as atopic dermatitis and photosensitivity may occur in patients who consume fennel.”

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

    3 sources cited
    1. 19. Brinker F. Herb Contraindications and Drug Interactions. 2nd ed. Sandy, OR: Eclectic Medical Publications, 1998.
    2. 6178. Gral N, Beani JC, Bonnot D, et al. [Plasma levels of psoralens after celery ingestion]. Ann Dermatol Venereol 1993;120:599-603.
    3. 49507. Ottolenghi, A., De Chiara, A., Arrigoni, S., Terracciano, L., and De Amici, M. [Diagnosis of food allergy caused by fruit and vegetables in children with atopic dermatitis]. Pediatr Med Chir 1995;17(6):525-530.

    Acetaminophen

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

  • Headache reported in 5.7% of FDA reports for Acetaminophen Additional detail

    Fennel

    “Orally, fennel oil has been associated with tonic clonic and generalized seizures. New-onset cluster headaches are reported in a 24-year-old female while using a toothpaste containing fennel and camphor for 3 months. The headaches resolved upon stopping the toothpaste. It is unclear if this adverse effect can be attributed to fennel, camphor, or the combination.”

    Fennel · Natural Medicines adverse-effect record, reported in epilepsy.

    2 sources cited
    1. 12868. Burkhard PR, Burkhardt K, Haenggeli CA, Landis T. Plant-induced seizures: reappearance of an old problem. J Neurol 1999;246:667-70. PubMed
    2. 112368. Mathew T, John SK, Javali M, Vasireddy M, Nadig R, Sarma GRK. Substance use related cluster headache: A case series. Headache 2022;62(7):908-910. PubMed

    Acetaminophen

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

  • Nausea / Vomiting reported in 6.2% of FDA reports for Acetaminophen Additional detail

    Fennel

    “Orally, fennel may cause gastrointestinal complaints, including nausea and vomiting.”

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

    2 sources cited
    1. 19146. Cuzzolin L, Zaffani S, and Benoni G. Safety implications regarding use of phytomedicines. Eur.J Clin Pharmacol. 2006;62:37-42. PubMed
    2. 104196. Lee HW, Ang L, Lee MS, Alimoradi Z, Kim E. Fennel for reducing pain in primary dysmenorrhea: a systematic review and meta-analysis of randomized controlled trials. Nutrients 2020;12(11):3438. PubMed

    Acetaminophen

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

Reported for Fennel but not commonly for Acetaminophen: stomach upset, a stuffy or runny nose, sun sensitivity and a fast or pounding heartbeat.

Effects for Acetaminophen come from the ADVERSE REACTIONS section of its FDA label; effects for Fennel come from the Natural Medicines adverse-effect record, quoted above. Where a percentage is shown, it is the share of 679,604 voluntary FDA FAERS reports for Acetaminophen 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

Fennel in Pregnancy & Breastfeeding

Pregnancy Possibly Unsafe

When used orally. Observational research has found that regular use of fennel during pregnancy is associated with shortened gestation.

Lactation Possibly Unsafe

When used orally. Case reports have linked consumption of an herbal tea containing extracts of fennel, licorice, anise, and goat's rue to neurotoxicity in two breast-feeding infants. The adverse effect was attributed to anethole, a constituent of fennel and anise. However, levels of anethole were not measured in breastmilk, and the herbal tea was not tested for contaminants. Furthermore, other adverse effects related to use of fennel during lactation have not been reported. However, until more is known, 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 Acetaminophen Is Prescribed For, and What Fennel Has Been Studied For

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

Acetaminophen is prescribed for: Acetaminophen temporarily relieves minor aches and pains caused by headaches, the common cold, backaches, muscle aches, toothaches, minor arthritis pain, and premenstrual or menstrual cramps. It also temporarily reduces fever. These uses apply across oral tablet, suspension, and oral liquid products. The intravenous (IV) injection form is used in clinical settings to treat acute pain and fever, including in pediatric patients 2 years and older.

Fennel has been studied for:

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

    Fennel for osteoarthritis

    It is unclear if oral fennel extract is beneficial in patients with knee osteoarthritis.

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

From our Q&A

Questions About Fennel or Acetaminophen

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

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

The most serious there right now: Activated Charcoal (major), Asarabacca (major), Beer (major), Siberian Cocklebur (major) and Wine (major).

By severity: 5 major · 114 moderate · 36 minor.

From our pharmacist’s overview on the Acetaminophen page

“Acetaminophen (Tylenol) feels harmless because it sits on every shelf, but this list deserves real attention, mostly because of your liver. Of the 155 supplements and herbs on file, five carry a major rating, and the largest serious group, 38 ingredients, adds liver strain on top of acetaminophen's own well-known potential to harm the…”

Reviewed by 2 · Jul 18, 2026

Open the Acetaminophen interaction page

One more smart check

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

We hold 2,219 real supplement products containing Fennel, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Fennel. Even though Fennel itself has no known interaction with Acetaminophen, 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 Fennel and Acetaminophen 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 Fennel
Top 10%

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

29 days ago today
Medication Acetaminophen
Top 1%

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

What is Fennel?

Fennel
  • Digestive upset and bloating
  • Infant colic
  • Menstrual cramps
  • Cough and respiratory complaints
  • Breast milk support (traditional)

Fennel is a Mediterranean herb widely used as a food and spice, and traditionally taken for digestive complaints, colic, and menstrual cramps. Some small studies suggest possible benefit for certain stomach and menstrual symptoms, but the evidence is limited. It is generally well tolerated in food amounts, but concentrated supplements and the essential oil should be used with caution and after checking with your pharmacist or doctor.

Foeniculum vulgare · Apiaceae · Seeds (fruit), bulb, leaves, and essential oil · Tea, capsules, seeds, essential oil, extracts, and as a food/spice

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

Fennel: dosing

There is no single official or standardized dose for fennel as a supplement. The right amount depends on the form (tea, seeds, capsule, or oil) and the product.The best approach is to follow the directions on the product label and not exceed them.

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

Read the full Fennel monograph & all interactions
Medication

About Acetaminophen

What Is Acetaminophen Used For?

Brand names: Tylenol Ex Strength, Children's Tylenol, Tylenol, Children's Tylenol Meltaways

Acetaminophen temporarily relieves minor aches and pains caused by headaches, the common cold, backaches, muscle aches, toothaches, minor arthritis pain, and premenstrual or menstrual cramps. It also temporarily reduces fever.

These uses apply across oral tablet, suspension, and oral liquid products. The intravenous (IV) injection form is used in clinical settings to treat acute pain and fever, including in pediatric patients 2 years and older.

Most-Reported Side Effects for Acetaminophen

From FAERS, the FDA’s public side-effect reporting system (679,604 reports, all brands). Reports are voluntary and are not proof the drug caused the effect.

Fatigue 45,791 reports
Nausea 41,932 reports
Overdose 40,941 reports
Drug dependence 39,209 reports
Headache 38,738 reports
See full Acetaminophen drug information
Keep checking

Other Drugs & Fennel

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

0Major
740Moderate
0Minor
2,089No known interaction
740 Moderate 2,089 No interaction
Moderate

740 interactions

Showing 60 of 740 moderate interactions — see all 740 on the Fennel page.

No interaction 2,089 drugs checked — show the list

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

Showing the 60 most looked-up of 2,089 medications checked with no known interaction — see the full Fennel list.

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

Fennel References

The 17 references that drive our Fennel 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. Leung AY, Foster S. Encyclopedia of Common Natural Ingredients Used in Food, Drugs and Cosmetics. 2nd ed. New York, NY: John Wiley & Sons, 1996.
  2. Brinker F. Herb Contraindications and Drug Interactions. 2nd ed. Sandy, OR: Eclectic Medical Publications, 1998.
  3. Zhu M, Wong PY, Li RC. Effect of oral administration of fennel (Foeniculum vulgare) on ciprofloxacin absorption and disposition in the rat. J Pharm Pharmacol 1999;51:1391-6.
  4. Gral N, Beani JC, Bonnot D, et al. [Plasma levels of psoralens after celery ingestion]. Ann Dermatol Venereol 1993;120:599-603.
  5. Burkhard PR, Burkhardt K, Haenggeli CA, Landis T. Plant-induced seizures: reappearance of an old problem. J Neurol 1999;246:667-70. PubMed
  6. Rosti L, Nardini A, Bettinelli ME, Rosti D. Toxic effects of a herbal tea mixture in two newborns. Acta Paediatrica 1994;83:683. PubMed
  7. Cuzzolin L, Zaffani S, and Benoni G. Safety implications regarding use of phytomedicines. Eur.J Clin Pharmacol. 2006;62:37-42. PubMed
  8. Tognolini, M., Ballabeni, V., Bertoni, S., Bruni, R., Impicciatore, M., and Barocelli, E. Protective effect of Foeniculum vulgare essential oil and anethole in an experimental model of thrombosis. Pharmacol.Res 2007;56(3):254-260. PubMed
  9. Subehan, Usia, T., Iwata, H., Kadota, S., and Tezuka, Y. Mechanism-based inhibition of CYP3A4 and CYP2D6 by Indonesian medicinal plants. J Ethnopharmacol. 5-24-2006;105(3):449-455. PubMed
  10. Tognolini, M., Barocelli, E., Ballabeni, V., Bruni, R., Bianchi, A., Chiavarini, M., and Impicciatore, M. Comparative screening of plant essential oils: phenylpropanoid moiety as basic core for antiplatelet activity. Life Sci. 2-23-2006;78(13):1419-1432. PubMed
  11. Subehan, Zaidi, S. F., Kadota, S., and Tezuka, Y. Inhibition on human liver cytochrome P450 3A4 by constituents of fennel (Foeniculum vulgare): identification and characterization of a mechanism-based inactivator. J Agric.Food Chem. 12-12-2007;55(25):101 PubMed
  12. LEVY, S. B. Bronchial asthma due to ingestion of fennel and fennel seed. Ann.Allergy 1948;6(4):415.
  13. Ottolenghi, A., De Chiara, A., Arrigoni, S., Terracciano, L., and De Amici, M. [Diagnosis of food allergy caused by fruit and vegetables in children with atopic dermatitis]. Pediatr Med Chir 1995;17(6):525-530.
  14. Trabace L, Tucci P, Ciuffreda L, et al. "Natural" relief of pregnancy-related symptoms and neonatal outcomes: above all do no harm. J Ethnopharmacol. 2015;174:396-402. PubMed
  15. Denaxa D, Arkwright PD. Fennel as a cause of immediate hypersensitivity to toothpaste. Ann Allergy Asthma Immunol. 2020;125(1):99-100. 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 Fennel and Acetaminophen Together: Common Questions

Is it safe to take Fennel with Acetaminophen?
We do not list a known interaction between Fennel and Acetaminophen. 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 Fennel and Acetaminophen have any of the same side effects?
Yes — our sources link each of them separately to 6 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 Fennel and Acetaminophen 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 Fennel in each. That is a conversation for your prescriber, especially if Acetaminophen is being adjusted to a target.
How was the Fennel and Acetaminophen combination checked?
Interactions in our licensed database are recorded against drug classes. Acetaminophen is filed under 8 classifications, and Fennel has documented interactions with 6 drug classes — none of Acetaminophen'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 Fennel interact with any other medications?
Yes. Fennel has 740 documented drug interactions in our database — Acetaminophen 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 Acetaminophen interact with any supplements?
Yes. Acetaminophen has documented interactions with 155 supplements in our database — Fennel is not one of them. The Acetaminophen 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

Fennel monograph Uses, safety profile, and every drug interaction in one place Acetaminophen drug information The full plain-English guide to this medication Acetaminophen supplement interactions Every supplement checked against Acetaminophen, 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 17 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Acetaminophen and Fennel?

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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.