What Is Thuja Good For? Uses, Benefits, and Risks

Thuja occidentalis, commonly called white cedar or arborvitae, has a centuries-long track record as a medicinal plant, used for everything from wart removal to respiratory infections. Modern lab and animal research has identified real biological activity behind some of these traditional applications, particularly antiviral, immune-stimulating, and anti-inflammatory effects. But thuja also contains thujone, a compound that can cause seizures and organ damage at relatively modest doses, which means the line between “herbal remedy” and “poison” is thinner here than with most botanical medicines.

A Long History of Medicinal Use

Thuja’s medicinal story begins with Indigenous peoples in North America, who used it to treat scurvy during the sixteenth century. The leaves are rich in vitamin C, and early European settlers quickly adopted the practice. Beyond scurvy prevention, traditional medicine systems have used thuja preparations for chronic bronchial inflammation, urinary tract infections, skin conditions, rheumatism, and even uterine cancer and menstrual irregularities.¹ The name “arborvitae,” meaning “tree of life,” reflects how highly early users valued it.

In homeopathy, thuja has been one of the most frequently prescribed remedies for skin growths and warts for well over a century. That particular use turns out to have some of the strongest modern evidence behind it, which is unusual for a homeopathic tradition.

Wart Treatment and Antiviral Activity

The most concrete clinical application of thuja is against warts. The leaves and leaf oil have documented antiviral, antibacterial, and antifungal properties, and thuja has been widely used for treating condylomatous skin lesions and common warts.² This is not just folk tradition. In one notable case, a kidney transplant recipient whose common warts had resisted standard treatments saw them cured by a thuja extract, leaving only superficial scars and without affecting the function of the transplanted kidney.³ That last detail matters because transplant patients take immune-suppressing drugs that make warts harder to treat and more likely to recur.

The antiviral mechanism is not fully pinned down, but researchers believe thuja’s effect on warts involves both direct antiviral action and stimulation of the local immune response against human papillomavirus (HPV), the virus responsible for most warts. Case reports have also described thuja being used for laryngeal papillomas, which are HPV-driven growths in the throat.² While these are individual case reports rather than large trials, the consistency of the antiviral signal across different types of HPV-related growths is worth noting.

How Thuja Stimulates the Immune System

Beyond direct antiviral effects, thuja appears to rev up the immune system in ways that could explain several of its traditional uses. Animal studies show that thuja extract and its polysaccharides boost natural killer cell activity and other immune cell functions that help the body identify and destroy abnormal cells. In tumor-bearing animals, thuja treatment also shifted the balance of inflammatory signaling molecules: it lowered several pro-inflammatory compounds while raising levels of anti-tumor factors like interleukin-2.⁴

The polysaccharides in thuja seem to be key players in this immune-stimulating role. They increase the production of multiple immune-signaling molecules from white blood cells and promote the expansion of helper T cells, which coordinate much of the immune response.⁵ This dual action, calming excessive inflammation while boosting targeted immune activity, is an interesting profile. It helps explain why thuja shows up in treatments for both infectious diseases (where you want stronger immunity) and inflammatory conditions (where you want less collateral damage from an overactive immune response).

A caveat is in order here: these immune effects have been demonstrated in lab dishes and animal models. Whether they translate neatly to humans taking thuja preparations by mouth is not yet established by controlled clinical trials of thuja alone.

Respiratory Infections

One of the most commercially successful uses of thuja is as an ingredient in combination herbal products designed to treat colds and upper respiratory infections. No controlled trials have been conducted on thuja by itself for this purpose, but several clinical studies have tested a specific herbal combination containing thuja extract alongside other immune-stimulating plant extracts.⁶

In a randomized, double-blind trial, patients with common colds took either a placebo or one of two doses of a combination extract containing baptisia, echinacea, and thuja. The high-dose group used fewer tissues and reached meaningful symptom improvement faster than the placebo group. On average, people in the high-dose group hit the “I’m clearly getting better” milestone about half a day sooner than those on placebo, with no adverse events reported.⁷ A separate placebo-controlled trial found that patients who started treatment early in the course of a cold saw the most benefit, reaching equal levels of improvement about three days earlier than the placebo group.⁸

The honest limitation is that you cannot tease apart how much of the benefit came from thuja versus echinacea versus baptisia. These were combination products, and each ingredient has its own immune-modulating properties. Still, the trials do suggest that the combination is more effective than placebo for colds, particularly when you start taking it early.

Antimicrobial and Antifungal Properties

Thuja essential oil shows selective antimicrobial activity that could have practical applications in topical products. Lab testing found that the oil was particularly effective against certain Gram-positive bacteria and against the yeast Candida parapsilosis, with oils extracted from fresh leaves and cones showing the strongest effects.⁹ The word “selective” is important: thuja oil does not kill everything indiscriminately. It works better against some microbes than others, which is actually a desirable trait in a topical antimicrobial because it suggests the potential for targeted use rather than broad-spectrum disruption.

These findings are still at the laboratory stage. Showing that an oil kills bacteria in a petri dish is the first step, not the last. How the oil performs when applied to actual human skin, at concentrations that are safe and tolerable, remains an open question in formal clinical research.

Anti-Inflammatory and Antioxidant Effects

Thuja’s chemical makeup, which includes flavonoids, phenolic compounds, tannins, and other plant metabolites, gives it measurable antioxidant and anti-inflammatory activity.¹ In an animal model of ulcerative colitis, daily administration of a thuja preparation successfully reduced intestinal inflammation caused by a chemical irritant, an effect researchers attributed to the flavonoid and phenolic content.¹⁰

This is one of those areas where the traditional use and the laboratory evidence align neatly. Indigenous peoples used thuja for chronic inflammatory conditions like rheumatism, and we can now see that the plant’s chemistry has real anti-inflammatory potential. Whether that potential translates into a reliable treatment for human inflammatory diseases is the gap that remains unfilled by clinical trials.

The Thujone Problem

Every discussion of thuja’s benefits has to contend with thujone, the compound that makes this plant genuinely dangerous at higher doses. Alpha-thujone, the main form found in thuja oil, works by blocking a specific type of receptor in the brain that normally keeps nerve activity in check. When that receptor is blocked, neurons fire too freely, which can lead to excitability, tremors, and at high enough doses, full-blown seizures.¹¹ This is the same mechanism that makes picrotoxin, a classic laboratory poison, dangerous. The seizures caused by thujone can be stopped with anti-seizure medications, which confirms the receptor-blocking mechanism.¹²

Thujone is also the compound that gave absinthe its notorious reputation (though modern research suggests absinthe’s dangers were historically exaggerated and mostly attributable to its high alcohol content). In thuja products, the thujone content varies enormously depending on the plant part used, how it was processed, and what form the final product takes. Thuja essential oil can contain extremely high levels of thujone, upward of 67 to 72 percent in oils distilled for shorter periods.¹³ That makes undiluted or minimally diluted thuja essential oil one of the more dangerous essential oils a consumer can buy.

Liver Damage and Organ Toxicity

Beyond the brain, thuja preparations can damage internal organs, particularly the liver. A published case report described a 40-year-old woman who developed acute liver injury after using thuja alongside another herbal product for fertility purposes.¹⁴ Because she was taking two herbal products simultaneously, it is difficult to assign blame solely to thuja, but the case illustrates a broader concern. Animal studies of thuja-related essential oils have confirmed that the liver is a vulnerable target, with tissue examination showing areas of cell death and inflammatory infiltration.¹⁵

People who are already taking medications processed by the liver, or who have pre-existing liver conditions, face a compounded risk from thuja products. And because herbal supplements are not standardized the way pharmaceuticals are, the actual dose of thujone in any given thuja product can be unpredictable.

Pregnancy and Reproductive Safety

Thuja is absolutely contraindicated during pregnancy. Historically, thuja decoctions and even very small quantities of thuja oil were used as abortifacients, and this use has been linked to neurotoxicity, convulsions, and death. Internal use of as few as 20 drops per day of thuja oil for five days has been associated with these severe outcomes. Beyond acute toxicity to the mother, thuja carries a substantial risk of causing fetal malformations.¹⁶

This is one area where the traditional knowledge and the safety data are unambiguous. If you are pregnant, planning to become pregnant, or breastfeeding, thuja products should be avoided entirely, including topical applications of the essential oil, since thujone can be absorbed through the skin.

Regulatory Landscape and Safe Dosing

Thujone’s risks have prompted regulatory action, though the rules vary by country and product category. The European Union deregulated the food use of thujone in 2008 flavoring regulations, while the European Medicines Agency introduced limits for thujone in medicinal products in 2009, creating a somewhat contradictory situation where the compound is treated differently depending on whether it shows up in your food or your herbal supplement.¹⁷

For consumers, the practical takeaway is that the form of thuja matters enormously. Homeopathic preparations, which are extremely dilute, generally contain negligible thujone. Standardized combination products sold in pharmacies typically have controlled thujone levels. But thuja essential oil purchased from aromatherapy suppliers or online retailers can contain dangerous concentrations, and these products are often sold with minimal safety labeling. Distillation time plays a role: longer distillation reduces thujone content considerably, with oils distilled for 200 minutes or more containing meaningfully less thujone than those distilled briefly.¹³ But this is not information typically provided on a retail bottle.

What Forms Are Available and How People Use Them

Thuja shows up in several forms on the market, and the risk-benefit calculation shifts dramatically depending on which one you pick:

Homeopathic pellets and tinctures: Heavily diluted, these are the most common form used for warts and skin growths. Thujone content is negligible to non-existent at typical homeopathic dilutions, which also raises questions about whether enough active compound remains to produce the effects attributed to it.
Standardized herbal extracts: Products like the baptisia-echinacea-thuja combination tested in clinical trials contain measured amounts of plant material. These are the best-studied form and carry the most evidence for respiratory benefits.
Essential oil: The most concentrated and most dangerous form. Never meant to be taken internally. Even topical use should involve heavy dilution, and some safety experts recommend avoiding topical thuja oil altogether given the high thujone content.
Herbal teas and decoctions: Traditional preparations made by steeping leaves. Thujone content varies depending on preparation method and is essentially impossible for the consumer to know.

If you are considering thuja for a specific health concern, the type of product and the dose are not minor details. They are the difference between a potentially helpful remedy and a genuinely toxic exposure. Anyone with liver disease, a seizure disorder, or who is pregnant should avoid all forms. For everyone else, sticking to well-characterized commercial preparations with established dosing is far safer than experimenting with essential oil or homemade decoctions.

Where the Evidence Stands Overall

Thuja occupies an interesting middle ground in herbal medicine. It is not a folk remedy with zero scientific backing, and it is not a well-proven pharmaceutical with decades of clinical trial data. The strongest evidence supports its antiviral activity against warts, its immune-stimulating properties in laboratory and animal models, and its contribution to combination products for colds. The anti-inflammatory and antimicrobial findings are promising but preliminary. And the toxicity profile, driven primarily by thujone, is well-documented and serious enough that casual self-treatment with concentrated forms is a bad idea.

The research gap that stands out most is the absence of controlled clinical trials on thuja preparations used alone. Almost all the human trial data comes from combination products, which makes it impossible to isolate thuja’s contribution. Given that the plant has been used medicinally for at least five hundred years and has demonstrable biological activity, it is the kind of candidate that could benefit from more rigorous human studies, designed with proper dose standardization and safety monitoring. Until those studies exist, the evidence supports cautious, informed use of well-characterized products and a healthy respect for the narrow margin between therapeutic and toxic doses.

Thuja in the Garden Versus Thuja in the Medicine Cabinet

One common source of confusion is the gap between thuja as a landscaping plant and thuja as an herbal medicine. Arborvitae hedges are among the most popular privacy screens in North American yards, and some people assume that since the plant grows in their backyard, it must be safe to harvest and use. The species sold at garden centers, usually Thuja occidentalis or its Asian relative Thuja plicata, is indeed the same genus used in herbal medicine. But wild-harvesting and preparing your own thuja products at home introduces uncontrolled variables: you do not know the thujone concentration of your particular tree, you cannot standardize a dose, and improper preparation could concentrate the toxic compounds rather than dilute them. The leap from “this tree is in my yard” to “I can make medicine from it” is one that has sent people to emergency rooms. If thuja preparations interest you, commercially produced and standardized products are the only reasonable starting point.