Herb & supplement monograph

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

But these pages have grown well beyond that into a full monograph — what Thuja 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

Check Thuja against your medication

Add one medication

✓ Supplement

Thuja

1 Your medication

Start typing any prescription or over-the-counter drug name.

Reviewed by licensed pharmacists Sourced from Natural Medicines

On this page

Thuja Drug Interactions: The Bottom Line

From the HelloPharmacist Editorial Team · Updated July 2026

Based on the available evidence, the overall risk of a clinically significant Thuja drug interaction appears low for most people. None of the listed interactions are rated major, and every one of them is theoretical rather than documented in human studies.

Interactions deserving the most attention

The main theme in Thuja's profile is seizure risk. Thuja products can contain thujone, a substance that may make seizures more likely, so the combinations deserving the most caution involve anticonvulsants and other medicines that lower the seizure threshold, such as certain anesthetics, antibiotics, and heart rhythm drugs. Thuja may also stimulate the immune system, which could theoretically work against immunosuppressants like cyclosporine or tacrolimus, medicines where a steady effect truly matters, especially after a transplant.

What the rest of the list means

The long list of interacting medications reflects a few broad drug categories, not hundreds of separately proven problems. Nearly all of the concern comes from reasoning about what thuja's components might do in the body, and none of these predicted effects have been confirmed in well-controlled human studies. That said, limited evidence is not the same as proof of safety, particularly for people who rely on seizure control or transplant medicines.

Check your medications against Thuja

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

Interaction report

Drugs that interact with Thuja

576 medications have a known interaction with Thuja, 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 Thuja using our pharmacist-reviewed interaction data.

AI summaries are generated from our Thuja 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 Thuja 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 Thuja affects

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

All 3 drug categories Thuja interacts with

AnticonvulsantsImmunosuppressantsSeizure Threshold Lowering Drugs

Anticonvulsants

Thuja products can contain thujone, which might lower the seizure threshold. Theoretically, this could decrease the effectiveness of anticonvulsants drugs.

Likelihood Possible Evidence D

Immunosuppressants

Thuja might stimulate immune function. Theoretically, taking thuja might decrease the effects of immunosuppressive therapy. Immunosuppressant drugs include azathioprine (Imuran), basiliximab (Simulect), cyclosporine (Neoral, Sandimmune), daclizumab (Zenapax), muromonab-CD3 (OKT3, Orthoclone OKT3), mycophenolate (CellCept), tacrolimus (FK506, Prograf), sirolimus (Rapamune), prednisone (Deltasone, Orasone), and other corticosteroids (glucocorticoids).

Likelihood Possible Evidence D

Seizure Threshold Lowering Drugs

Thuja products can contains significant amounts of thujone, a neurotoxin. Theoretically, patients taking drugs that lower the seizure threshold might be at greater risk of seizure if they also take thuja. Advise patients taking these drugs to avoid thuja products. Some drugs that lower the seizure threshold include anesthetics (propofol, others), antiarrhythmics (mexiletine), antibiotics (amphotericin, penicillin, cephalosporins, imipenem), antidepressants (bupropion, others), antihistamines (cyproheptadine, others), immunosuppressants (cyclosporine), narcotics (fentanyl, others), stimulants (methylphenidate), theophylline, and others.

Likelihood Possible Evidence D

Monograph

Thuja: Uses, Safety & Side Effects

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

The bottom line

Thuja, also called northern white cedar or arborvitae, is a tree whose leaf and oil have a long history in folk and homeopathic medicine, especially for warts and immune support. Solid human evidence for these uses is very limited, and the undiluted oil contains thujone, which can be toxic. Talk with a pharmacist or doctor before using it, and avoid it during pregnancy and breastfeeding.

Scientific name: Thuja occidentalis
Family: Cupressaceae
Part used: Leaves (young twigs/branch tips) and essential oil
Common forms: Homeopathic pellets, tinctures, topical ointments, essential oil, capsules, and combination cold/immune products

People commonly use it for

Warts and skin growths
Respiratory and immune support
Cold and upper respiratory symptoms
Topical skin conditions
Traditional use as a diuretic or to bring on menstruation

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

Safety at a glance

OverallUse caution

The plant and especially its essential oil contain thujone, which can be toxic if taken internally in large amounts.

PregnancyLikely Unsafe

When used orally due to abortifacient activity; avoid using.

Read the full pregnancy detail

BreastfeedingLikely Unsafe

When used orally due to toxicity; 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.

Jump to a section

Overview

Thuja usually refers to Thuja occidentalis, an evergreen tree also known as northern white cedar or arborvitae. It grows in eastern North America and is widely planted as an ornamental and hedge.

The young leafy twigs and the essential oil pressed from them have been used in traditional and homeopathic medicine for a long time. People have used thuja for warts and skin growths, for coughs and colds, and as part of immune-support products. It is most commonly sold today as homeopathic pellets, tinctures, topical creams, and as part of combination herbal cold remedies.

How it works

Thuja leaf and oil contain compounds including thujone, along with flavonoids and polysaccharides. Laboratory studies suggest some of these compounds may have antiviral, antimicrobial, and immune-stimulating effects, and that polysaccharides may influence immune cells.

These findings come mostly from test-tube and animal research. It is not clear whether they apply to the small amounts used in people, especially in highly diluted homeopathic products. Thujone is also the part of the plant most linked to toxic effects on the nervous system at high doses.

Effectiveness

Does Thuja work?

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

Evidence overview · 1 use evaluated

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

Also studied for 1 condition — evidence insufficient to rate

Insufficient Reliable Evidence To Rate Common cold

Rating & evidence shown verbatim from Natural Medicines

Clinical research in patients with moderate cold symptoms shows that taking three tablets of a specific combination product (Esberitox, Schaper & Brümmer GmbH & Co. KG) containing dry extracts of echinacea root, thuja leaf, and wild indigo root three times daily for 7-9 days improves the severity of cold symptoms, general well-being, and overall response rate when compared with placebo. It is unclear if these effects are due to thuja leaf, the other ingredients, or the combination.

Sources Ref 6392

Source & disclaimer. Effectiveness ratings and evidence summaries are provided by Natural Medicines (Therapeutic Research Center) and shown as licensed. Where Natural Medicines hasn’t rated a use, HelloPharmacist’s pharmacists may add their own reviewed rating and evidence (each such entry is labeled). This is educational information, not medical advice — talk with your pharmacist or doctor before starting, stopping, or changing a supplement.

Safety & precautions

Highly diluted homeopathic thuja and properly diluted topical products are generally considered low risk for most adults. However, the undiluted essential oil and concentrated extracts should not be swallowed, because the thujone they contain can be toxic.

People with seizure disorders should be especially careful, since thujone can affect the nervous system. Pregnant women should avoid thuja because it has traditionally been used to stimulate the uterus and menstruation, which could be harmful. Breastfeeding women should also avoid it since its safety is not known. Avoid use in children unless directed by a healthcare provider.

Because supplement quality varies, choose reputable products and always check with a pharmacist or doctor first.

Side effects

Topical thuja can cause skin irritation or allergic reactions in some people. Taking the plant or its oil internally in large amounts may cause stomach upset and, in serious cases, nervous system effects such as seizures due to thujone.

Signs of toxicity — such as confusion, tremors, vomiting, or convulsions — are a medical emergency. Stop use and seek care if you have a strong reaction.

Thuja: Reported Adverse Effects

Documented safety reports on Thuja from the evidence-graded Natural Medicines (TRC Healthcare) database, shown word-for-word from the licensed record.

Orally, large doses of thuja have been reported to cause toxicity involving headache, nervous agitation, seizures, gastric irritation, vomiting, abdominal pain, and diarrhea. Thuja toxicity has also been reported to cause liver damage, renal toxicity, and death in some cases.

Fetrow CW, Avila JR. Professional's Handbook of Complementary & Alternative Medicines. 1st ed. Springhouse, PA: Springhouse Corp., 1999.
Naser, B., Bodinet, C., Tegtmeier, M., and Lindequist, U. Thuja occidentalis (Arbor vitae): A Review of its Pharmaceutical, Pharmacological and Clinical Properties. Evid.Based Complement Alternat.Med 2005;2(1):69-78.

Reports by condition

Dermatitis Dermatologic

Contact dermatitis, presenting as an itchy papular squamous eruption on the hands, developed in a 46-year-old female who handled thuja plants while gardening. It resolved when contact with thuja was avoided. The causative ingredient of thuja was identified as limonene.

In one case report, a 5-year-old female presented with a papillary eccrine adenoma. In an effort to avoid excisional biopsy, an ointment containing thuja was applied to the lesion for 6 months, resulting in peripheral extension and central necrosis of the lesion, eventually necessitating complete excision.

Diarrhea Gastrointestinal

Orally, large doses of thuja have been reported to cause toxicity involving gastric irritation, vomiting, abdominal pain, and diarrhea.

Fetrow CW, Avila JR. Professional's Handbook of Complementary & Alternative Medicines. 1st ed. Springhouse, PA: Springhouse Corp., 1999.
Naser, B., Bodinet, C., Tegtmeier, M., and Lindequist, U. Thuja occidentalis (Arbor vitae): A Review of its Pharmaceutical, Pharmacological and Clinical Properties. Evid.Based Complement Alternat.Med 2005;2(1):69-78.

Epilepsy Neurologic/CNS

Orally, large doses of thuja have been reported to cause toxicity involving nervous agitation, seizures, and death.

Fetrow CW, Avila JR. Professional's Handbook of Complementary & Alternative Medicines. 1st ed. Springhouse, PA: Springhouse Corp., 1999.
Naser, B., Bodinet, C., Tegtmeier, M., and Lindequist, U. Thuja occidentalis (Arbor vitae): A Review of its Pharmaceutical, Pharmacological and Clinical Properties. Evid.Based Complement Alternat.Med 2005;2(1):69-78.

Pain Hepatic

Orally, large doses of thuja have been reported to cause toxicity involving liver damage and death. In one case report, a healthy 40-year-old female taking thuja and black cohosh for 1 month presented with 3 days of severe abdominal pain and AST and ALT levels exceeding 5 times the upper limit of normal. Symptoms improved within 5 days of supplement discontinuation and levels normalized within 2 weeks. It is unclear if this reaction was due to thuja, black cohosh, or other factors.

Fetrow CW, Avila JR. Professional's Handbook of Complementary & Alternative Medicines. 1st ed. Springhouse, PA: Springhouse Corp., 1999.
Naser, B., Bodinet, C., Tegtmeier, M., and Lindequist, U. Thuja occidentalis (Arbor vitae): A Review of its Pharmaceutical, Pharmacological and Clinical Properties. Evid.Based Complement Alternat.Med 2005;2(1):69-78.
Patel R, Alavi F, Ortega S, Matela A. Herb-Induced Liver Injury by Cimicifuga racemosa and Thuja occidentalis Herbal Medications for Fertility. Case Rep Gastrointest Med 2021;2021:8858310.

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.

Adverse-effects data: Natural Medicines, Therapeutic Research Center

Dosing

There is no well-established standard dose for thuja, and products vary widely in strength. Homeopathic pellets, tinctures, and topical creams all use different concentrations.

Because the essential oil contains potentially toxic thujone, it should not be taken by mouth without professional guidance. The safest approach is to follow the directions on the product label and ask a pharmacist or doctor before starting.

Pregnancy & Breastfeeding

Thuja & Pregnancy

Likely Unsafe

When used orally due to abortifacient activity; avoid using.

McGuffin M, Hobbs C, Upton R, Goldberg A, eds. American Herbal Products Association's Botanical Safety Handbook. Boca Raton, FL: CRC Press, LLC 1997.

Thuja & Breastfeeding

Likely Unsafe

When used orally due to toxicity; avoid using.

Leung AY, Foster S. Encyclopedia of Common Natural Ingredients Used in Food, Drugs and Cosmetics. 2nd ed. New York, NY: John Wiley & Sons, 1996.

Pregnancy & lactation ratings: Natural Medicines, Therapeutic Research Center

References & further reading

The 10 references that drive our Thuja 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.

Leung AY, Foster S. Encyclopedia of Common Natural Ingredients Used in Food, Drugs and Cosmetics. 2nd ed. New York, NY: John Wiley & Sons, 1996.
McGuffin M, Hobbs C, Upton R, Goldberg A, eds. American Herbal Products Association's Botanical Safety Handbook. Boca Raton, FL: CRC Press, LLC 1997.
Millet Y, Jouglard J, Steinmetz MD, et al. Toxicity of some essential plant oils. Clinical and experimental study. Clin Toxicol 1981;18:1485-98. PubMed
Gohla SH, Haubeck HD, Neth RD. Mitogenic activity of high molecular polysaccharide fractions isolated from the Cupressaceae Thuja occidentale L. I. Macrophage-dependent induction of CD-4-positive T-helper (Th+) lymphocytes. Leukemia 1988;2:528-33.
Fetrow CW, Avila JR. Professional's Handbook of Complementary & Alternative Medicines. 1st ed. Springhouse, PA: Springhouse Corp., 1999.
Henneicke-von Zepelin H, Hentschel C, Schnitker J, et al. Efficacy and safety of a fixed combination phytomedicine in the treatment of the common cold (acute viral respiratory tract infection): results of a randomised, double blind, placebo-controlled, m
Naser, B., Bodinet, C., Tegtmeier, M., and Lindequist, U. Thuja occidentalis (Arbor vitae): A Review of its Pharmaceutical, Pharmacological and Clinical Properties. Evid.Based Complement Alternat.Med 2005;2(1):69-78.
Patel R, Alavi F, Ortega S, Matela A. Herb-Induced Liver Injury by Cimicifuga racemosa and Thuja occidentalis Herbal Medications for Fertility. Case Rep Gastrointest Med 2021;2021:8858310. PubMed
Ambooken B, Thomas M, Jisha KT. Papillary Eccrine Adenoma in a 5-year-old Girl Altered by Application of Thuja Ointment. J Cutan Aesthet Surg 2020;13(4):370-371. PubMed
Badaoui A, Fougerousse AC. Contact dermatitis to linalool and limonene: Unusual sources of exposure. Ann Dermatol Venereol 2023;150(2):167-168. PubMed

Keep reading

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.

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.

Brand directory

Brands that make products with Thuja

19 brands in our database make a supplement containing Thuja.

BIOVEA Homeopathics 4 products Doctor Morse's Healing Herbs 47 products Dr. Morse's Cellular Botanicals 79 products Enzymatic Therapy 675 products Gaia Herbs 700 products Hawaii Pharm 4,726 products Herb Pharm 3,320 products Herbal Terra 3,138 products Herbalist & Alchemist 613 products Herbs, Etc. 388 products Integrative Therapeutics 941 products Kukamonga Bienestar y Salud 1 product MH Michael's Health Naturopathic Programs 92 products Michael's Naturopathic Programs 338 products MNP Michael's Naturopathic Programs 273 products Nature's Answer 1,655 products Nature's Way 3,426 products Vaxa 8 products Woodstock Herbal Products 38 products

Product directory

Supplement products with Thuja

86 products in our database contain Thuja. Open any to see its full ingredient list and every drug interaction we check.

Pharmacist Counseling Corner

Thuja: Common Questions

What is Thuja used for, and does it work?

People use Thuja for a range of reasons, but according to the Natural Medicines database the current clinical evidence is insufficient to confirm it works for the specific conditions it has been studied for. See the graded list on this page, and talk to your pharmacist or doctor before relying on it for any condition.

Does Thuja interact with prescription medications?

Yes. We list 576 medications with a known interaction with Thuja. Use the checker above to see how Thuja interacts with a specific drug.

How are Thuja interactions rated?

Each interaction is graded major, moderate, or minor based on how clinically significant it is and the strength of the evidence behind it. Major interactions are the most serious and are best avoided, or used only under close professional supervision.

Is it safe to take Thuja with my medications?

It depends on the specific medication. Some combinations are fine, while others call for monitoring, timing changes, or should be avoided. Check your exact drug above and confirm with your pharmacist or doctor before starting, stopping, or changing anything.

Where does this Thuja interaction information come from?

Our interaction data is built on the Natural Medicines database — an evidence-graded reference for vitamins, herbs, and supplements — and is reviewed by licensed HelloPharmacist pharmacists, who may add clinical context.

What is Thuja used for?

It is most often used for warts and skin growths and as part of immune or cold-and-respiratory products. Strong human evidence for these uses is limited.

Is Thuja safe to take?

Diluted homeopathic and topical forms are generally low risk for most adults, but the concentrated essential oil contains thujone and can be toxic if swallowed. Check with a pharmacist or doctor first.

Can I use Thuja during pregnancy or while breastfeeding?

No. Thuja has traditionally been used to stimulate the uterus and menstruation, so it should be avoided in pregnancy, and its safety while breastfeeding is unknown.

Can Thuja cause side effects?

Yes. It may cause skin irritation when used topically, and taking concentrated forms internally can cause stomach upset and, rarely, seizures from thujone.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Keep exploring

Products that contain Thuja

A rotating sample of real supplements in our database that list Thuja — open any to see its full ingredients and every drug interaction we check.

See all 86 products with Thuja →

Where next

Supplement interaction checkerCheck any supplement or product against your medications Drug–drug interactionsCheck two or more of your medications against each other Browse medications A–ZEvery drug we’ve checked against herbs & supplements NDC & pricing lookupFind a drug’s NDCs, packaging and costs Ask a pharmacistFree, personal answer from our licensed team

Have a question about Thuja?

Our pharmacists answer your medication & supplement questions — free.

Ask a pharmacist

Thuja Drug Interactions, Uses, Effectiveness, Safety & More

Your Choice:

Thuja Drug Interactions: The Bottom Line

Drugs that interact with Thuja

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

What Severity, Likelihood & Evidence Mean

Severity — How Serious It Can Be

Likelihood — How Well It’s Documented

Where This Data Comes From

The kinds of drugs Thuja affects

Thuja: Uses, Safety & Side Effects

Overview

How it works

Does Thuja work?

Safety & precautions

Side effects

Thuja: Reported Adverse Effects

Dosing

Thuja & Pregnancy

Thuja & Breastfeeding

References & further reading

Brands that make products with Thuja

Supplement products with Thuja

Thuja: Common Questions

Related supplements & herbs

Products that contain Thuja

Have a question about Thuja?