There are multiple reports of serious allergic reactions to chamomile taken by mouth or as an enema, including anaphylaxis, throat swelling, and shortness of breath. Skin allergic reactions have been frequently reported, including dermatitis and eczema. Chamomile eyewash can cause allergic conjunctivitis (pink eye).

People with allergies to other plants in the Asteraceae (Compositae) family should avoid chamomile. Examples include: aster, chrysanthemum, mugwort, ragweed, and ragwort. Cross-reactions may occur with celery, chrysanthemum, feverfew, tansy, and birch pollen. Individuals with allergies to these plants should avoid chamomile. Contact skin allergy has been reported.

Impurities (adulterants) in chamomile products are common and may cause adverse effects. Atopic dermatitis (skin rash) has been reported.

Chamomile in various forms may cause drowsiness or sedation. Use caution when driving or operating heavy machinery. In large doses, chamomile can cause vomiting. Due to its coumarin content, chamomile may theoretically increase the risk of bleeding. Caution is advised in patients with bleeding disorders or taking drugs that may increase the risk of bleeding. Dosing adjustments may be necessary. Increases in blood pressure are possible.

In theory, chamomile may act as a uterine stimulant or lead to abortion. It therefore should be avoided during pregnancy. There is not enough scientific data to recommend the safe use of chamomile while breastfeeding.

Capsules/tablets containing 400 to 1,600 milligrams taken by mouth daily in divided doses have been used. As a liquid extract (1:1 in 45% alcohol), 1 to 4 milliliters taken by mouth three times daily have been used. As a tincture (1:5 in alcohol), 15 milliliters taken three to four times per day have been used. As a mouth rinse, a 1% fluid extract or 5% tincture has been used.

Chamomile is frequently consumed as tea, and 1 to 4 cups of chamomile tea taken daily (from tea bags) is a common dose.

There are no standard doses for chamomile used on the skin. Some natural medicine publications have recommended paste, plaster, or ointment containing 3% to 10% chamomile flower heads. Chamomile has been also used as a bath additive and as a douche.

There is not enough reliable scientific data available to recommend the safe use of chamomile products in children.

Chamomile interactions are not well studied scientifically.

Chamomile may increase the amount of drowsiness caused by some drugs. Examples include benzodiazepines such as lorazepam (Ativan®) or diazepam (Valium®), barbiturates such as phenobarbital, narcotics such as codeine, some antidepressants, and alcohol. Caution is advised while driving or operating machinery.

In theory, chamomile may increase the risk of bleeding when used with anticoagulants or antiplatelet drugs. Some examples include aspirin, anticoagulants ("blood thinners") such as warfarin (Coumadin®) or heparin, anti-platelet drugs such as clopidogrel (Plavix®), and non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen (Motrin®, Advil®) or naproxen (Naprosyn®, Aleve®).

Chamomile may interfere with the way the body processes certain drugs using the liver's "cytochrome P450" enzyme system. As a result, the levels of these drugs may be increased in the blood, and may cause increased effects or potentially serious adverse reactions. Patients using any medications should check the package insert and speak with a healthcare professional including a pharmacist about possible interactions.

Be aware that many tinctures contain high levels of alcohol and may cause vomiting when taken with metronidazole (Flagyl®) or disulfiram (Antabuse®).

An extract containing Martricaria chamomile, Sideritis euboea, Sideritis clandestine, and Pimpinella anisum was associated with selective estrogen receptor modulator (SERM) properties against osteoporosis. Theoretically, chamomile may interact with SERM drugs such as raloxifene (prescription drug used for osteoporosis) or tamoxifen (a prescription drug used for cancer).

Constituents in chamomile may alter blood sugar or blood pressure. Patients taking medications that affect blood sugar or blood pressure should be cautious.

Chamomile may have anti-inflammatory effects. Theoretically, use of chamomile with other anti-inflammatory drugs, such as NSAIDs or ibuprofen, may have additive effects.

Chamomile may interact with medications that act as cardiac depressants, central nervous system depressants, calcium channel blockers, cardiac glycosides, and respiratory depressants.

Chamomile may also interact with heart medications, antibiotics, drugs for diabetes, high cholesterol medications, ulcer medications, drugs broken down by the liver, drugs for diarrhea, antifungals, antihistamines, diuretics, estrogens, or gastrointestinal disorder medications.

Chamomile may increase the amount of drowsiness caused by some herbs or supplements. Caution is advised while driving or operating machinery.

In theory, chamomile may increase the risk of bleeding when taken with other products that are believed to increase the risk of bleeding. Multiple cases of bleeding have been reported with the use of Ginkgo biloba, and fewer cases with garlic and saw palmetto. Numerous other agents may theoretically increase the risk of bleeding, although this has not been proven in most cases.

Chamomile may interfere with the way the body processes certain drugs using the liver's "cytochrome P450" enzyme system. As a result, the levels of other herbs or supplements may become too high in the blood. It may also alter the effects that other herbs or supplements possibly have on the P450 system. Patients using any medications should check the package insert and speak with a healthcare professional including a pharmacist about possible interactions.

Chamomile may have anti-estrogenic effects and interact with herbs and supplements such as red clover or soy.

Based on preliminary study, constituents in chamomile may alter blood sugar or blood pressure. Patients taking herbs or supplements that affect blood sugar or blood pressure should be cautious.

Chamomile may have anti-inflammatory effects. Theoretically, use of chamomile with other anti-inflammatory herbs and supplements may have additive effects.

Chamomile may interact with herbs and supplements that act as cardiac depressants, cardiac glycosides, respiratory depressants, or spasmolytics.

Chamomile may also interact with herbs and supplements acting on the heart, antibiotics, those used for diabetes, high cholesterol agents, supplements for ulcers, supplements broken down by the liver, supplements used for diarrhea, antifungals, antihistamines, diuretics, estrogens, or gastrointestinal disorder supplements.