Avoid in individuals with a known allergy or hypersensitivity to members of the Lamiaceae (mint) family or to any component of thyme, or to rosemary (Rosmarinus officinalis).
Cross-reactions to birch pollen, celery, oregano, and to other species in the Lamiaceae/Labiatae (mint) family may occur. Symptoms of allergy may include nausea, emesis (vomiting), pruritus (severe itching), angioedema (swelling under the skin), dysphagia (difficulty swallowing), dysphonia (altered voice), hypotension (low blood pressure), and progressive respiratory difficulty. Occupational asthma has been reported.
Side Effects and Warnings
Although not well studied in humans, thyme flowers and leaves appear to be safe in culinary and in limited medicinal use. Caution is warranted with the use of thyme oil, which should not be taken by mouth and should be diluted when applied on the skin due to potentially toxic effects.
Side effects of thyme taken by mouth may include headache, dizziness, hypotension (low blood pressure), bradycardia (slowed heart rate), heartburn, nausea, vomiting, diarrhea, gastrointestinal irritation, muscle weakness, and exacerbated inflammation associated with urinary tract infections. Use cautiously in patients with gastrointestinal irritation or peptic ulcer disease.
Taking thyme oil by mouth may also cause seizure, coma, cardiac arrest, or respiratory arrest. High doses of thyme or thyme oil may elicit tachypnea (rapid breathing). Inflammation of the eye and nasal mucosa has also been reported with exposure to thyme dust.
Topical application of Listerine® antiseptic solution to a chronic parenchyma of the toe has caused inflammation of the skin. Avoid topical preparations in areas of skin breakdown or injury, or in atopic patients. As an ingredient in toothpaste, cases of inflamed lips and tongue have been attributed to thyme oil.
Although not well studied in humans, Thymus serpyllum, a related species to Thymus vulgaris, has been shown to exert effects on the thyroid. Use cautiously in patients with thyroid disorders. Estradiol and progesterone receptor-binding activity has also been demonstrated.
Thyme is not recommended in pregnant or breastfeeding women due to a lack of available scientific evidence. Thyme may act as an emmenagogue (promotes menstruation) and abortifacient (promotes abortion).
Adults (18 years and older):
There is no proven safe or effective dose for thyme or thymol. Teas, liquid extracts, oils, ointments, compresses and combination products are all commercially available. Thyme oil is considered to be highly toxic and should not be taken internally. Combination products studied in available trials include Bronchipret® (Primulae radis and thyme) and Listerine® (containing thymol, a constituent of thyme).
For alopecia areata (hair loss), 2-3 drops of an essential oil combination (thyme, lavender, rosemary, and cedarwood added to grapeseed and jojoba oil) massaged into the scalp every night for seven months has been studied. For paronychia (skin infection around a finger or toenail), 1 drop of 1-2% thymol in chloroform to the affected area three times daily, or 1 drop of 4% thymol in chloroform to a chronically affected area three times daily has been used. Diluted thyme oil has been applied as needed in 1-2% ointments for a variety of skin disorders. Safety and efficacy have not been proven, and thyme oil is considered to be highly toxic.
As a compress for rheumatic diseases, bruises, and miscellaneous skin disorders, 5 grams of dried leaf per 100 milliliters boiling water for 10 minutes and strain has been used in compress form.
Children (younger than 18 years):
There is no proven safe or effective dose for thyme in children and use if not recommended. However, for prevention of periodontal infections, a combination product containing 1% chlorhexidine/thymol varnish (Cervitec®) was tolerated in 110 healthy children, ages 8-10 years old, when taken three times within two weeks.
Interactions with Drugs
Theoretically, thyme may decrease levels of thyroid hormone. Patients taking thyroid replacement therapy or anti-thyroid agents should use cautiously. Monitoring may be necessary.
Although not well studied in humans, thyme may interact with agents with estrogen or progesterone receptor activity. Examples of agents that may be affected include hormone replacement therapies and birth control pills.
Topical (applied on the skin) thymol may increase the absorption of 5-fluorouracil. Caution is advised in chemotherapy patients, as 5-fluorouracil is often used in cancer chemotherapy. Consult with a qualified healthcare professional, including a pharmacist, to check for interactions.
Interactions with Herbs and Dietary Supplements
Although not well studied in humans, thyme may interact with herbs with estrogen or progesterone receptor activity. Caution is advised when combining thyme with other herbs and supplements with proposed hormonal effects, such as black cohosh.