Drug & supplement interaction

Thuja + Penicillin G

Penicillin G brand name: Pfizerpen.

Moderate Interaction
Medically reviewed by · Updated September 2026
The bottom line Moderate

Thuja has a moderate interaction with Penicillin G. Thuja products can contains significant amounts of thujone, a neurotoxin.

Read the full interaction report
SeverityModerate
LikelihoodPossible
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Thuja and Penicillin G

Here is the interaction we found between these two, with the evidence behind it.

Moderate

SEIZURE THRESHOLD LOWERING DRUGS

Why this applies to Penicillin G

Penicillin G falls under SEIZURE THRESHOLD LOWERING DRUGS — the group Thuja interacts with.

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.
Severity Moderate Likelihood Possible Evidence D

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.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the thing to know about combining Thuja with Penicillin G. The concern isn't about how your body breaks down the antibiotic. Instead, both can independently nudge your seizure threshold lower. Thuja products may contain thujone, a compound that can be toxic to nerves in concentrated amounts, and penicillin G itself (especially in high IV doses) is already known to occasionally irritate the nervous system and trigger seizures in sensitive people.

Stacking the two could, in theory, add up and make a seizure slightly more likely. I'll be honest though: this is based on weak, anecdotal evidence, not strong studies. Still, to play it safe, I'd skip thuja while you're on penicillin G and check with your pharmacist or doctor first.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. 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

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction 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.
  • PossibleInteraction 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.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

Thuja Also Interacts With Other Medications

Thuja has 575 moderate known drug interactions in our database — the Penicillin G one above is one of them. If you take anything else, check it against the full list below.

Moderate 575 No known interaction 2,255 (incl. Penicillin G)
Taking anything else?

Check Another of Your Medications Against Thuja

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

Everything else you take

See Every Supplement That Interacts With Penicillin G

This page covers Thuja only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Penicillin G page lists 56 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Asarabacca (major), Siberian Cocklebur (major), Aristolochia (moderate) and Bacillus Coagulans (moderate).

By severity: 3 major · 42 moderate · 11 minor.

From our pharmacist’s overview on the Penicillin G page

“My concern with penicillin G (Pfizerpen), an injectable antibiotic reserved for serious infections such as syphilis and endocarditis, centers on a few supplements that deserve genuine respect. Siberian cocklebur and asarabacca can each harm the kidneys, extra strain nobody fighting a severe infection needs, while activated charcoal can…”

Reviewed by 2 · Jul 18, 2026

Open the Penicillin G interaction page

One more smart check

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

We hold 84 real supplement products containing Thuja, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Thuja. Your product may carry other ingredients that interact with Penicillin G too, on top of Thuja — and those would not show on this page. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Thuja and Penicillin G 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 Thuja
Top half

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

29 days ago today
Medication Penicillin G
Top 25%

#453 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.

Supplement

About Thuja

What is Thuja?

  • 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

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.

Read the full Thuja monograph & all interactions
Medication

About Penicillin G (Potassium, Sodium) Injection

What Is Penicillin G (Potassium, Sodium) Injection Used For?

Brand name: Pfizerpen

Penicillin G Potassium for Injection is used to treat serious infections caused by bacteria that are susceptible to penicillin. It covers a wide range of conditions, including bloodstream infections (septicemia), meningitis, pneumonia, endocarditis (heart valve infection), and pericarditis (infection around the heart).

It is also used for infections such as syphilis (including neurosyphilis and congenital syphilis), anthrax, diphtheria, botulism, tetanus, gas gangrene, disseminated gonococcal infections, listeria infections, and rat-bite fever, among others. Some uses are as adjunctive therapy — meaning penicillin G supports, but does not replace, other treatments like antitoxins.

See full Penicillin G (Potassium, Sodium) Injection drug information
Keep checking

Other Drugs & Thuja

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

0Major
575Moderate
0Minor
2,254No known interaction
575 Moderate 2,254 No interaction
Moderate

575 interactions

Showing 60 of 575 moderate interactions — see all 575 on the Thuja page.

No interaction 2,254 drugs checked — show the list

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

Showing the 60 most looked-up of 2,254 medications checked with no known interaction — see the full Thuja list.

See the full Thuja interactions page
See every supplement checked against Penicillin G, ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

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.

© 2021 Therapeutic Research Center, LLC

Keep exploring
Thuja monograph › Uses, safety, and every drug interaction in one place Penicillin G supplement interactions › Every supplement checked against Penicillin G, ranked by severity Penicillin G (Potassium, Sodium) Injection drug information › The full plain-English guide to this medication Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Thuja and Penicillin G Together: Common Questions

Can you take Thuja with Penicillin G?
There is a moderate interaction, so it may be acceptable with monitoring or timing changes — but check with your pharmacist first. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the Thuja and Penicillin G interaction?
We rate it Moderate. This combination may require monitoring, a dose adjustment, or separating the times you take each one. Consult your pharmacist before using them together.

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

Still Have a Question About Penicillin G and Thuja?

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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.