Cedar: A Comprehensive Reference on Botanical Identity, Traditional Use, Pharmacology, and Scientific Evidence
1. Identity and Nomenclature
"Cedar" is a common name, not a precise botanical identification. The word "cedar" is a common name rather than a precise botanical identification, and depending on region and context it may refer to northern white cedar, western red cedar, or any of several other unrelated species. This taxonomic ambiguity is critically important for anyone evaluating cedar as a dietary supplement or medicinal ingredient.
1.1 True Cedars: Genus Cedrus (family Pinaceae)
True cedars come from the genus Cedrus. There are four species in the genus Cedrus: Cedrus deodara Loud. (Himalaya Mountains, Nepal), Cedrus libani A. Rich. (Asia Minor, Lebanon, Syria), C. brevifolia Hen. (Cyprus), and C. atlantica Manettii (Atlas Mountains). Among these:
- Cedrus libani A. Rich. — Cedar of Lebanon (Lebanese cedar). A species of large evergreen conifer in the genus Cedrus, belonging to the pine family and native to the mountains of the Eastern Mediterranean basin. Known for its longevity, height, and durable wood, it has held profound significance for millennia.
- Cedrus deodara (Roxb. ex D.Don) G.Don — Himalayan cedar (Deodar cedar). Also known as Himalayan cedar, it belongs to the family Pinaceae and has been widely used in the Indian system of medicine due to its nutritional and pharmaceutical effects.
- Cedrus atlantica (Endl.) Manetti ex Carrière — Atlas cedar (Atlantic cedar). Yields an essential oil from its wood that has been historically used in medicine and perfumery.
1.2 "False" Cedars: Related Genera
Many other trees called "cedar" are actually from different genera, such as Juniperus (red cedar), Thuja (western red cedar), and Calocedrus (incense cedar). Key species include:
- Thuja occidentalis L. — Eastern white cedar, northern white cedar, arborvitae. Originates in Eastern North America and is cultivated in Europe and Brazil as an ornamental tree, being known as the "tree of life" or "white cedar."
- Thuja plicata Donn ex D.Don — Western red cedar. Not a true cedar (Cedrus sp.) but belongs to the Cypress family (Cupressaceae). Found in the western United States and western Canada from Alaska through northern California and in the Rocky Mountains from British Columbia through Montana.
- Juniperus virginiana L. — Eastern red cedar. Also called western red cedar is the species Thuja plicata and should not be confused with the eastern red cedar, Juniperus virginiana, or the Lebanon cedar, Cedrus libani, which are unrelated species.
Each type of cedar has distinct chemical compositions and potential uses. Understanding the particular type of cedar one intends to use is crucial because the chemical compounds vary significantly between species, influencing their therapeutic effects and safety profiles.
1.3 Plant Part and Preparation Forms
The leaves, twigs, bark, and roots are all used medicinally. Common preparation forms used in traditional and contemporary contexts include:
- Essential oil — Obtained by steam or hydro-distillation of wood chips, sawdust, bark, or leaves. The oil's chemical profile varies significantly depending on the botanical source, geographical origin, and distillation technique.
- Tinctures and liquid extracts — Alcoholic or glycerin-based extracts of leaves and twigs. In modern herbal and homeopathic markets, thuja appears in tinctures, creams, mother tinctures, diluted pellets, and essential-oil-based products.
- Teas and decoctions — Most preparations of red cedar call for boiling the medicinal parts to make a decoction or for making a tea or infusion.
- Capsules and powders — Dried leaf or bark material encapsulated for oral use.
- Topical preparations — Salves, creams, and ointments incorporating essential oil or plant extracts.
2. Traditional and Historical Use
2.1 Ancient Civilizations of the Eastern Mediterranean
The tree features in ancient Mesopotamian literature, with references appearing as far back as the Epic of Gilgamesh approximately 5,000 years ago. Historically the ancient Phoenicians used Cedar wood for shipbuilding and traded Cedar trees with Ancient Egypt, Ancient Greece, Anatolians, Iberians, Punics, Sicilians, Romans and Ancient Iraq. About 4,600 years ago King Snefru of the Fourth Dynasty of ancient Egypt ordered 40 shiploads of cedar timber for shipbuilding and for the heavy doors of the king's palace.
Beyond construction, the medicinal and preservative properties of cedar were exploited by the Egyptians. Egyptians used Cedrus libani essential oils for mummification. The ancient Egyptians used cedar oil and resin in their embalming process; the oil's natural antiseptic and antifungal properties were considered crucial for preserving the body for its journey to the afterlife.
In the biblical tradition, Hebrew priests were ordered by Moses to use the bark of the Lebanon cedar in the treatment of leprosy. Solomon also procured cedar timber to build the Temple in Jerusalem.
The Cedar of Lebanon was prized for its wood, which was easily worked, pleasantly scented, free of knots and resistant to rot, while its resin was valued for its preservative and medicinal properties. As a result, it was widely sought after throughout the Mediterranean and the Middle East.
2.2 Ritual and Incense Use
The fragrant wood was used by Native Americans as well as the ancient Egyptians, Greeks, and Romans as an ingredient in incense blends. The name "Thuja" was given by the Swedish botanist Linnaeus in 1753; it comes from the Greek word thuo, meaning "to sacrifice," as cedar wood was often burned with animal sacrifices by the ancients to add a pleasing aroma.
2.3 Native American Traditions
Western Red Cedar is a cultural keystone tree, meaning it played a central role medicinally, nutritively and spiritually for indigenous cultures. Cedar has played an enormous role in the various Northwest tribes and bands that stretch from Northern California to Alaska. Cedar was used for housing, transportation (canoes), clothing, tools and utensils, bowls, baskets, boxes, firewood, and as medicine — as a tea and steam for respiratory conditions.
Native American peoples used cedar to treat a wide variety of conditions, including coughs, fevers, and bronchitis, and to help prevent infections.
Indigenous peoples made a tea from the scaled leaves of Thuja occidentalis (Eastern White Cedar). This herbal tea was found to contain 50 mg of vitamin C per 100 grams and thus helped prevent and treat scurvy effectively. This vitamin C content explains the famous account of French explorer Jacques Cartier's crew being cured of scurvy in the 16th century. The name "Arbor vitae" is the Latin term for "tree of life," credited to the French explorer Jacques Cartier and referring to the medicinal properties of the plant.
2.4 Traditional Introduction to Europe
Eastern White Cedar was introduced to Europe in the 16th century (around 1540), where it was quickly appreciated for its ornamental and medicinal qualities. European settlers later adopted the use of Thuja in traditional medicines for its immune-boosting and antiviral activities.
In Western herbal medicine, cedar leaf oil was used as an emmenagogue, abortifacient, vermifuge, diuretic, and digestive aid. It was applied externally to relieve the pains of arthritis and rheumatism, to treat external fungal infections of the skin (ringworm and thrush), and to remove anal or genital warts.
Thuja was listed in the US Pharmacopoeia as a diuretic to enhance urine flow and as a treatment to stimulate the functions of the uterus.
2.5 Ayurvedic and Indian Traditional Medicine
Cedrus deodara has been traditionally used for the treatment of tic, fever, cough, bronchitis, ulcer and tuberculosis. It has been widely utilized in Chinese drinks and recommended in the Ayurvedic system of medicine. Clinically, it is also widely used to alleviate arthralgia, sleeplessness, traumatic injury, eczema, ascariasis, and edema.
Key traditional records of folk medicine, including the Sushruta Samhita and Charaka Samhita, document the use of C. deodara.
2.6 Traditional Chinese Medicine
Thuja occidentalis, known as the "tree of life" or "white cedar," is used in traditional medicine to treat liver diseases, bullous bronchitis, psoriasis, enuresis, amenorrhea, cystitis, uterine carcinomas, diarrhea, and rheumatism. In traditional Chinese medicine, the leaves and essential oil of Thuja sutchuenensis are documented in the Supplement to the Compendium of Materia Medica for their properties of "cooling blood, detoxifying, and healing wounds."
2.7 Homeopathic Tradition
In homeopathy, Thuja occidentalis is used as a remedy for acute bronchitis and other disorders of the upper airways. The plant can help with catarrh and loosen mucus. The leaves of this tree have also been used as a treatment for rheumatism. T. koraiensis oil is a known remedy with topical application in the treatment of the human papilloma virus (HPV).
3. Key Constituents and Active Compounds
3.1 True Cedar (Cedrus spp.) — Key Phytochemicals
Among consistently reported compounds, cedrol, α-cedrene, β-cedrene, thujopsene, and widdrol are frequently reported as major constituents. Cedrol, a sesquiterpene alcohol, is one of the hallmarks of Juniperus-derived cedarwood oils.
Species-specific variation is significant:
- C. atlantica (Atlas cedar) is characterized by high levels of α-cedrene, himachalene, and related sesquiterpenes.
- C. deodara (Himalayan cedar) contains a mixture of cedrene isomers and himachalol.
- Major chemical constituents reported from C. deodara include α-terpineol, linalool, limonene, anethole, caryophyllene, and eugenol, taxifolin, cedeodarin, wikstromal, deodarone, cedrinoside and flavonoids.
- Bioactive compounds particularly cedrin, himachalol, himachalene, and atlantone are recognized as key constituents for the observed pharmacological activities of C. deodara.
- The essential oil isolated from Cedrus libani leaves may bear potential for drug development due to its high concentrations of germacrene D and β-caryophyllene.
The bioactivity of cedarwood oil is attributed mainly to its unique composition of sesquiterpenes and alcohols, including cedrol, α-cedrene, and widdrol, whose molecular structures suggest interactions with neuronal, immunological, and microbial pathways.
3.2 Thuja occidentalis (White Cedar) — Key Phytochemicals
The fresh leaves of Thuja occidentalis contain roughly 0.6% essential oil, and the dominant compound in that oil is thujone, which accounts for about 65% of the essential oil from fresh leaves. Thujone exists in two forms: alpha-thujone (about 85% of total thujone) and beta-thujone (about 15%).
The content of thujone in dried twigs was determined as 7.6 mg/g (0.76%), consisting of 85% α-thujone and 15% of the more toxic β-thujone. Further monoterpenoids include α-pinene, myricene, α-terpinene, limonene, γ-terpinene, terpinolene, fenchone, and traces of sabinene, camphene, borneol, and thujylalcohol. Other constituents include lignans, flavonoids like quercetin, and T-lymphocyte-stimulating polysaccharides.
The chemical constituents of T. occidentalis have been of research interest for decades due to their contents of essential oil, coumarins, flavonoids, tannins, and proanthocyanidines.
The plant also contains a range of flavonoids, including quercetin, kaempferol, and myricetin. These act primarily as antioxidants, neutralizing damaging molecules produced during normal cell metabolism.
4. Mechanisms of Action
4.1 Central Nervous System / Autonomic Nervous System Effects (Cedrol)
The main mechanism of aromatherapy may be related to the limbic system of the brain. Aroma components stimulate olfactory cells, which transmit signals to the brain and affect the autonomic nervous system and hormone secretion. Odor particles reach the limbic system through the olfactory nerve, producing sedative and relaxing effects that affect blood pressure, heart rate, memory and stress response.
The anxiolytic effect of cedrol was effectively antagonized by SCH23390. Cedrol decreased the dopamine (DA) and norepinephrine (NE) levels in hippocampus, striatum and hypothalamus. These findings suggest that the dopaminergic system (D1 receptor) rather than the serotoninergic or GABAergic system may potentially be involved in the modulation of cedrol-induced anxiolytic-like behaviors in mice.
Cedrol's pharmacological actions of anxiolytic effects, promoting hair growth, decreasing blood pressure, and mitigating obesity may be related to its action on glucocorticoids.
4.2 Antimicrobial Mechanisms
The antimicrobial activity of cedar essential oil is attributed primarily to its terpenoid constituents. The essential oil of cedar exhibits antifungal, antimicrobial, antiviral, and molluscicidal properties and also exhibits anti-inflammatory activity.
It is speculated that cedrol may be the effective antibacterial component of cedarwood essential oil, based on antifungal tests conducted on the activity of cedrol against root rot fungus.
4.3 Anti-inflammatory Mechanisms
C. deodara has a range of pharmacological activities including anti-inflammatory, analgesic, anti-hyperglycaemic, antiulcer, antispasmodic, antibacterial, insecticidal, molluscicidal and anticancer activities.
4.4 Immunomodulatory Mechanisms (Thuja)
Thujapolysaccharides seem to have antiviral properties. The combination of thujone, polysaccharides, and flavonoids likely explains why thuja has such a wide range of traditional uses, as each class of compound contributes different biological effects.
5. Scientific Evidence by Area of Use
General caveat: A 2025–2026 systematic review concluded that cedarwood essential oil shows antimicrobial, anti-inflammatory, sedative, and dermatological properties primarily attributed to sesquiterpenes such as cedrol and α-cedrene; however, most data derive from small-scale or preclinical studies, with limited clinical validation. Significant gaps remain in the standardization of chemical composition, determination of safe and effective dosages, and evaluation of long-term safety, particularly regarding dermal sensitization, inhalation exposure, and potential metabolic interactions.
5.1 Sedative, Anxiolytic, and Cardiovascular Relaxation Effects
Human/clinical evidence (moderate quality for a narrow endpoint): One study analyzed cardiovascular and respiratory functions while subjects inhaled fumes of pure cedrol extracted from cedar wood oil. Vaporized cedrol (14.2 ± 1.7 μg/l, 5 l/min) and blank air (5 l/min) were presented to healthy human subjects (n=26) via a face mask, while ECGs, heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), and respiratory rates (RR) were monitored. Statistical analyses indicated that exposure to cedrol significantly decreased HR, SBP, and DBP compared to blank air while it increased baroreceptor sensitivity. Furthermore, respiratory rate was reduced during exposure to cedrol. Spectral analysis of HR variability indicated an increase in high frequency (HF) component (index of parasympathetic activity), and a decrease in ratio of LF to HF components during cedrol inhalation. Furthermore, cedrol inhalation significantly decreased LF components of both SBP and DBP variability, which reflected vasomotor sympathetic activity.
In human tests, cedrol inhalation caused a relaxant effect with decreased heart rate, blood pressure, respiratory rates, sympathetic activity and increased parasympathetic activity. More specifically, when subjects were asked to inhale cedrol into the lower airway, brain single-photon emission computed tomography (SPECT) studies indicated that hippocampal regional cerebral blood flow was bilaterally increased.
These results provide the first evidence that an odorant in the lower airway modulates autonomic activity via the central nervous system.
Animal/preclinical evidence: Cedrol can decrease blood pressure in humans by inhalation and ameliorate high-fat diet-induced obesity in mice. Cedrol is a sesquiterpene alcohol derived from ginger and cedar oil. Cedrol has multiple pharmacological effects including sedation, promoting hair growth, decreasing blood pressure and reducing obesity.
Evidence strength: The human cardiovascular studies are small in scale but controlled and use objective physiological endpoints. The anxiolytic mechanisms are understood primarily from animal studies. Overall evidence is preliminary but mechanistically coherent.
5.2 Alopecia and Hair Growth
Human/clinical evidence (one relevant randomized trial, but confounded): Research published in the Archives of Dermatology (November 1998) examined aromatherapy for hair loss. The researchers noted that "cedarwood, lavender, thyme, and rosemary oils have hair growth-promoting properties" and that these oils had been anecdotally used to treat alopecia for more than 100 years. Patients were enrolled in a randomized, double-blind, placebo-controlled trial. The active group received thyme vulgaris (2 drops, 88 mg), Lavandula angustifolia (3 drops, 108 mg), Rosmarinus officinalis (3 drops, 114 mg), and Cedrus atlantica (2 drops, 94 mg) mixed in a carrier oil combining jojoba (3 ml) and grapeseed (20 ml) oils.
The study was conducted over seven months, with follow-ups at three and seven months. 86 patients with alopecia areata participated and were divided into two groups. The active group massaged the blend of essential oils and carrier oils into the scalp daily, which resulted in significant hair growth compared to a control group that used the carrier oils alone. Participants were responsible for massaging the mixture into their scalp for 2 minutes each day, wrapping a warm towel around their heads, and repeating the routine every night for 7 months. 44% of the participants showed an improvement in their alopecia.
Limitations: The study used a blend of oils, so it is not possible to determine whether the results were attributable to the cedarwood essential oil or the other oils. Since this is the only study on cedarwood oil for hair loss, the contribution of cedarwood specifically is unclear. The sample was too small to make large generalizations; only 86 participants took part.
WebMD/Natural Medicines rates Atlantic cedar oil for baldness (alopecia areata) and as an insect repellant, noting there is no good scientific evidence to support these uses.
Evidence strength: Single small randomized trial using a multi-ingredient blend; the independent contribution of cedarwood cannot be isolated. Evidence is insufficient to attribute benefit to cedar specifically.
5.3 Antimicrobial Activity
In vitro / preclinical evidence: Cedrol has exhibited in vitro antimicrobial activity against Gram-positive bacteria and yeast, and cytotoxic activity against human lung, liver and oral cancer cells.
GC-MS analysis revealed that one cedar wood essential oil is primarily composed of cedrol at a high content of 78.48%. Other components include α-cedrene, α-cadinol, β-cedrene, γ-eudesmol, globulol, and epicedrol — mainly terpenoid compounds. The IC50 of this cedar wood essential oil against root rot fungus was determined to be 37.5 μg/mL.
The essential oils from Cedrus species also show bioactivity against bacteria and viruses. However, more preclinical analyses (e.g., in vivo experiments) as well as clinical trials are required to evaluate the potential of essential oils from Cedrus species.
Evidence strength: Antimicrobial data exists primarily from in vitro studies. No controlled human trials have established clinical efficacy for cedar essential oil as an antimicrobial agent.
5.4 Anti-inflammatory and Analgesic Effects
Preclinical evidence: Animal studies have found that cedarwood can bring down pain, swelling, and inflammation. Human blood-related illnesses may also be treated with Cedrus libani. It exhibits promising analgesic and anti-inflammatory properties. However, more toxicological and clinical research is required to determine the safety and efficacy for treating human ailments.
Evidence strength: Anti-inflammatory evidence is limited to animal and in vitro models. No controlled human studies have been conducted to validate these effects clinically.
5.5 Anticancer / Antiproliferative Effects
In vitro / preclinical evidence: The aim of one study was to explore the essential oil from the bark of Cedrus deodara (CDEO) as a potential anticancer agent, as frontline drugs against cancer in clinical settings are posing challenges of resistance and other detrimental side-effects.
A separate study investigated total lignans from Cedrus deodara pine needles for anticancer potential. The Cedrus deodara total lignans from the pine needles (CTL) were extracted. The study investigated the anticancer potential of CTL on the A549 cell line (human lung cancer). CTL was extracted by ethanol. By CCK-8 assays, CTL inhibited the growth of A549 cells in a dose-dependent fashion, with IC50 values of 39.82 ± 1.74 μg/mL.
The Cedrus genus demonstrates cytotoxic, spasmolytic, immunomodulatory, antiallergic, anti-inflammatory and analgesic activities. Cancer patients frequently seek remedies from traditional medicinal plants that are believed to exert fewer side effects than conventional therapy with synthetic drugs. A long-lasting goal of anti-cancer and anti-microbial therapy research is to find compounds with reduced side effects. In this respect, Cedrus species might be of interest.
Evidence strength: Entirely in vitro and animal. No human clinical trials on cedar for cancer have been identified. These findings should not be interpreted as evidence of clinical efficacy.
5.6 Antileishmanial and Immunomodulatory Activity
In vitro evidence: The antileishmanial activity of C. deodara, as assessed by bioassay testing on Leishmania donovani parasites and immunomodulatory effect of benzene extract of leaves on host cells, indicated that it might be a potential new safe therapeutic target to cure visceral leishmaniasis. In this study, the extract of Cedrus deodara leaves was standardized and tested for immunomodulatory antileishmanial activities.
Evidence strength: Preliminary in vitro data only. No human trials exist.
5.7 Antihyperlipidemic and Metabolic Effects
Animal evidence: One study examined the antihyperlipidemic effect of Cedrus deodara against monosodium glutamate (MSG)-induced obesity in neonatal rats. Ethanolic extract (EE) and acetone extract (AE) of C. deodara were administered at doses of 100 and 200 mg/kg p.o./day. On day 60 of treatment, body weight, locomotor activity, body temperature, and various biochemical parameters including serum glucose, total cholesterol, and triglyceride were recorded. There was a significant reduction in body weight and organ weights and increased body temperature and locomotor activity after treatment with extracts.
A 2025 study investigated the effect of cedrol on hepatic lipid metabolism. Cedrol effectively mitigated the lipid accumulation in liver and adipose tissues induced by dexamethasone in adult male mice. The researchers hypothesized that cedrol could mitigate corticosteroid-induced central obesity and lipid metabolism dysfunction in vivo, and revealed that cedrol could indeed mitigate corticosteroid-induced hepatic lipid accumulation and adipocyte hypertrophy in vivo.
Evidence strength: Animal models only; no human trials have examined cedar for metabolic conditions.
5.8 Insect Repellent Properties
Laboratory evidence: Black-legged tick nymphs exhibited dosage-dependent mortality when exposed to cedrol, and at the highest dosage tested (6.3 mg/mL), cedrol killed 100% of the ticks. These repellency and toxicity results together demonstrate a clear potential for the use of cedarwood oil as a pest control agent. Researchers found that a component in the oil called cedrol is highly repellent to ants, and is also lethal to ticks and moth larvae.
Evidence strength: Insect repellency data is relatively robust in laboratory settings, though field effectiveness and comparison to registered repellents require further study.
5.9 Neuroprotective Effects of Cedrin (Cedrus deodara)
Preclinical evidence: Cedrin, a compound from Cedrus deodara, was found to ameliorate mitochondrial membrane potential loss and mitochondrial permeability transition pore opening, and to reduce caspase-3 activity and modulate Bcl-2/Bax ratios. These results demonstrate the protective effect of cedrin, which is related to the inhibition of oxidative stress, improvement of mitochondrial dysfunction, and suppression of apoptosis.
Cedrol was also shown to contribute to potentially beneficial effects on Alzheimer's disease, specifically through inhibiting the enzymes acetylcholinesterase (AChE) and butyrylcholinesterase (BChE).
Evidence strength: Purely preclinical. No human trials have assessed cedar for neuroprotection or cognitive function.
6. Body Systems and Health Areas of Association
Based on available (primarily preclinical) research, cedar species have been associated with the following body systems:
- Nervous system: Anxiolytic, sedative, and autonomic regulatory effects of inhaled cedrol, demonstrated in human subjects and animal models.
- Cardiovascular system: Reduction of heart rate and blood pressure during cedrol inhalation in small human studies.
- Respiratory system: Historical traditional use for coughs, bronchitis, and tuberculosis across multiple cultures; traditional treatment of bullous bronchitis with T. occidentalis.
- Integumentary system (skin and hair): Antimicrobial and anti-inflammatory properties applicable to acne and skin infections; one human trial of a multi-essential-oil blend for alopecia areata.
- Immune system: Immunomodulatory polysaccharides in Thuja occidentalis; in vitro antileishmanial and antiviral activity.
- Metabolic system: Preclinical evidence of antihyperlipidemic effects and glucose regulation in animal models of obesity.
- Urinary system: Historical use of T. occidentalis as a diuretic, listed in the US Pharmacopoeia for this indication.
7. Dosage Forms and Reported Dosages
Significant gaps remain in the standardization of chemical composition and determination of safe and effective dosages. The following dosages are reported directly from the sources identified:
- Alopecia areata (human trial, topical blend): The active blend used in the 1998 randomized trial included thyme vulgaris (2 drops, 88 mg), lavandula angustifolia (3 drops, 108 mg), rosmarinus officinalis (3 drops, 114 mg), and Cedrus atlantica (2 drops, 94 mg) mixed in a carrier oil (jojoba 3 mL and grapeseed 20 mL).
- Cedrol inhalation (human cardiovascular study): Vaporized cedrol at 14.2 ± 1.7 μg/l at 5 l/min was delivered via face mask to healthy human subjects.
- C. deodara extracts (animal study, antihyperlipidemic): Ethanolic extract and acetone extract of C. deodara were administered at 100 and 200 mg/kg p.o./day.
- Traditional tincture dosage (Western herbal tradition): A tincture prepared 1:2 fresh at 50–75% was used at 2–5 drops per day for up to one week to bolster immune system function, reduce mucosal congestion, and to move blood and lymph in cases of stagnation, arthritis, or poor menses.
Little information exists on dosages for most traditional preparations of red cedar. Historical Western pharmacy records list capsules of Libanol (distilled oil of C. libani and C. atlantica) at up to 45 grains per day, and cedar apples from Juniperus virginiana at 10 to 20 grains three times a day as an anthelmintic — these are historical data from older herbal references and have no modern clinical validation.
8. Safety Considerations and Interactions
8.1 Thujone Toxicity (Critical Safety Concern)
Thujone is the reason thuja requires caution. In high enough doses, it causes seizures, and severe overdoses of thujone-containing preparations can lead to loss of consciousness and death.
European regulatory guidance has established exposure limits. The European Medicines Agency has set a tolerable daily intake of thujone at 10 micrograms per kilogram of body weight. For practical purposes, daily exposure from medicinal products should stay below 6 milligrams, and use should be limited to no more than two weeks at a time.
Thresholds for thujone in food were derived from the 2002 Scientific Committee on Food (SCF) opinion, incorporating precautionary margins from animal toxicity data, including a no-observed-effect level (NOEL) of 5 mg/kg body weight per day for convulsions in female rats, extrapolated with safety factors exceeding 100-fold for humans. The European Food Safety Authority (EFSA) has reaffirmed the low risk of thujone at food-grade levels through flavoring evaluations.
Toxicity of thujone has been extensively studied. Neurotoxicity is the principal toxic outcome in acute and chronic studies. There is some equivocal evidence of carcinogenicity in rats.
Thuja essential oil is far more concentrated than leaf teas or tinctures and poses the greatest risk. It should never be taken undiluted or in large amounts.
8.2 Hepatotoxicity and Organ Toxicity
Although most essential oil monoterpene compounds are safe for human food and medical applications, in certain amounts or under particular circumstances they can cause serious disorders. The neurotoxicity of α-terpineol has been established, and it is also associated with the induction of hepatic oxidative stress, cytotoxicity, and genotoxic damage.
8.3 Contraindication in Pregnancy
Pregnant women should avoid thuja entirely, as it has historical use as a uterine stimulant. In humans, thuja extracts were used in folk medicine as a contraceptive and an abortifacient. Decoctions of the bark of red cedar can also cause miscarriage.
8.4 Toxicity of Essential Oil When Taken Internally
Cedar essential oil is meant to be used topically. It is toxic if taken internally, and has the ability to produce convulsions or even death if taken in even small quantities. A 1999 study done in Switzerland noted an increase in poisoning deaths from plant products, including Thuja, due possibly to an increase in people practicing herbal healing and aromatherapy. The oil of all species of thuja can cause convulsions.
8.5 Allergic and Dermal Reactions
The lipophilic character of the constituents of concern like thujone is indicative of relatively good dermal resorption from mucous membranes and even from intact skin. Allergic contact dermatitis to Thuja occidentalis has been reported after a 3-week application of the homeopathic mother tincture. The possible allergenic constituent of Thuja has not yet been identified.
8.6 Occupational Sensitization (Western Red Cedar)
Many people develop asthma and bronchial spasms from exposure to red cedar or red cedar dust. This is due to an allergic reaction to plicatic acid present in the wood. This is a well-documented occupational health concern in woodworking industries and is distinct from therapeutic use of the plant's medicinal parts.
8.7 Regulatory Data Gaps
Data on repeated dose toxicity of Thuja occidentalis extracts have not been provided. Studies on carcinogenic activities of Thuja occidentalis were not provided. Most data derive from small-scale or preclinical studies, with limited standardization of dosage and formulations. Safety aspects and toxicological gaps are also highlighted as essential considerations for future clinical translation.
References
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