Essential Oil Contraindications
Anise: In excessive doses, (more the 3-drops, three times per day or with prolonged use over two to three weeks), it can slow down the circulation causing circulatory and nervous system disorders. It may irritate the skin if it is applied undiluted, although this is not likely. Do not exceed a maximum of 3-drop, three times a day. Do not administer for longer than 14 consecutive days. Avoid internally and externally in prgnancy, breast-feeding, estrogen-dependent cancers, liver disease, endometriosis, and prostatic hyperplasia.
Basil: Avoid during pregnancy and breast-feeding. It can be intoxicating in excess and can nausea and vomiting. Externally, it may cause skin sensitization. Use no more than 3-drops in the bath, as it causes skin tingling. Avoid long-term use if there is a history of estrogen dependent cancer or endometriosis.
Bay: Avoid during pregnancy and breast-feeding. Avoid exceeding the stated dose. Internally if could act as a narcotic if used in excess of the RDD. Externally it nay cause skin sensitivity.
Benzoin Resinoid: If applied undiluted, it may irritate the skin, causing contact dermatitis.
Bergamot: Bergamot containing bergptene can cause abnormal skin pigmentation and possible skin cancer when exposed to the sun. This action is intensified if bergamot is blended with alcohol. For this reason, it should be avoided during pregnancy and breast-feeding. Do not use at the same time as photosensitizing drugs.
Black Pepper: Can be an irritant if used unfiluted on the skin. Can be nephrotoxic if used above the RDD, and is more difficult for the kidneys than other essential oils. It should be avoided with kidney disease. Avoid with homeopathics.
Cajuput: Not recommended internally for children. Avoid if there is a history of epilepsy or hypertension. Do not use at the same time as homeopathics remedies, it will neutralized their effects. Can cause stinging if applied undiluted to the skin. Do not exceed stated dose.
Cedarwood: Avoid during pregnancy and breast-feeding.
Roman Chamomile: Avoid chamomile in the first trimester of pregnancy. When used externally, may cause dermatitis. If there is a allergy to Ragweed or other members of the Asteraceae family take extra precaustions.
Cinnamon: Avoid during pregnancy, breast-feeding, if suffering from stomach or interstinal ulcers, or with use of homeopathic. May cause irritation and sensitization when used externally. May cause photosensitivity. If taken orally in excess, can cause tachycardia, increased intestinal peristalsis, increased respiration and perspiration throught stimulation of the vasomotor center, followed by a sedative stage characterized by sleepiness and depression.
Clary Sage: Use with caution during pregnancy. Only use after the first trimester. Avoid if there is a history of low blood pressure, estrogen dependent cancer, endometriosis, and epilepsy. Can cause photosensitivity. Can be narcotic in does above RDD.
Clove: May cause skin irritation is some people, both internally and externally. May cause liver toxicity if used above stated dosage or if administered longer than recommended time. Avoid if there is liver disease. Use with cause in pregnancy; externally, only after the first trimester. Avoid with homeopathics.
Cypress: Avoid in pregnancy, breast-feeding, hypertension. Some people may be allergic to cypress pollens.
Elemi: Avoid in pregnancy, with infants and young children.
Eucalyptus: Should not be applied to the face or nose, or used internally for babies or young children. Do not exceed RDD. Avoid with history of epilepsy, hypertension or gastrointestinal inflammation and liver complaints. Do not use at the same time as homeopathics, it will limit their effects. Can irritate skin and mucous membranes if used undiluted. Use with caution when taking prescription drugs.
Fennel: Contraindicated with nervous system problems, epilepsy, or estrogen-related disorders, including estrogen dependant cancer and endometriosis. Avoid essential oil with infants and young children – use infusion of fennel seeds to dilute milk or juice instead. Avoid in pregnancy. Do not use for more than three weeks without a break.
Garlic: Do not exceed RDD, especially if there is liver problems. Do not administer essential oil to babies. Best to avoid in pregnancy. Take care when applying fresh, crushed garlic or even garlic oil directly to the skin, as it can cause buring and blistering. It is always best to apply freshly crushed garlic between two layers of muslin.
Geranium: Contraindicated in the first trimester of pregnancy. May cause irritation to skin in some sensitive people and cause insomnia and relessness.
Ginger: Essential oil should not be used for morning sickness. May cause irritation to sensitive skin and cause photosensitivity. In cases of gallstones, it should not be administered without consulting a medical or naturopathic doctor.
Grapefruit: May casue photosensitivity and skin irritation.
Immortelle (Helichrysum): Avoid with anti-coagulant medication. Do not administer continuously for longer than two weeks without a three-wees interim. May cause skin irritation sensitization or phototoxicity.
Jasmine: Absolute should not be used internally. Avoid during pregnancy and brest-feeding. Long-term use may cause sensitization.
Juniper: Contraindicated duing prgnancy and breast-feeding. Should not be used for more than four to six seeks without a break or four weeks. Prlonged or excessive use can result in renal damage. Contraindicated with kidney dsease. Prolonged use may lead to hypokalemia. Exteranl application may cause dermal irritation. May potentiate hypoglycemic and diuretic therapies. May cause skin sensitization.
Lavender: May cause skin sensitivity in rare cases.
Lemon: May cause skin irritaion, sensitization, and photosensitivity. Use in moderation.
Marjoram: May casue allergy in people who are allergic to other Lamiaceae family plants. Avoid long-term use (longer than two weeks without aa break of at least four weeks). Avoid in cases of depression and hypotension. Do not use internally with children. Has the potential to stimulate menstruation, do not use during pregnancy.
Neroli: May cause dermatitis and photosensitivity.
Nutmeg: Avoid in pregnancy or on sensitive skin. Use for a limited time only, even at the recommended daily dose.
Patchouli: Avoid with loss of appetite or anorexia. Can cause photosensitivity.
Peppermint: May cause allergic reactions in the mouth, neck and throat. Do not use during the first trimester of pregnancy or while breast-feeding. Do not use with children younger than two years old. Avoid in cases of heart disease and epilepsy. Avoid with homeopathics. Externally, use for a limited time only. Do not use on damaged or sensitive skin. Avoid direct contact with the eyes.
Pine:Avoid use on sensitive or damaged skin, because it may cause eczema-type reactions allergy-sensitive skin. Contraindicated during pregnancy and breast-feeding.
Rose: Contraindicated during the first trimester of pregnancy. In rare cases, may cause dermatitis.
Rosemary: Use caution in cases of chronic asthma, epilepsy, or hypertension. Contraindicated in the first trimester of pregnancy and should not be adminstered to babies or children younger than the age of four. It can antidote homeopathic remedies if stored with them or administered at the same time.
Sandalwood: In rare cases, may cause dermatitis and allergic reactions.
Austrailian Tea Tree: Do not use internally above RDD.
New Zealand Tea Tree: Acute toxicity can occur if it is administered in amounts larger than the stated daily dose. In some individuals, can produce a mild irritancy to the skin.
Thyme: Contraindicated during pregnancy and breast-feeding. Can cause liver damage if used excessively above RDD and should be avoided in cases of liver disease. Avoid with hypertension. It can burn and irritate the skin.
Vetiver: In rare cases, may cause skin irritation. May cause liver troubles if used in excess of the RDD over a prolonged period of time, and should be avoided in cases of liver disease.
Yarrow: Contraindicated during pregnancy and breast-feeding. May casue allergic reaction in people allergic to members of the Asteraceae family. Excessive doses may interfer with anticoagulant, hypo and hypertensive therapies. May have sedative and diuretic effects.
Ylang Ylang: Undiluted use on sensitive skin is contraindicated. Avoid during pregnancy and breast-feeding.
Aloe: Gel: When used topically, it may delay wound healing following a laparotomy or cesarean delivery. Otherwise, it is classified by the AHPA as safe when used appropriately.
Juice: Do not use during pregnancy; lactation; with any intestinal obstruction, abdominal pain of unknown origins, or any inflammatory condition of the intestine (including appendicitis, colitis, Crohn's disease, irritable bowel syndrome, etc.); hemorrhoids; kidney dysfunction; menstruation; in children younger than 12; or for more than 8-10 days. Overdose of the juice can cause colonic perforation, bleeding diarrhea, and kidney damage. An overdose can be as little as 1.0-gm per day for several days. The AHPA recommends the following label for products containing aloe juice in sufficient quantity: "Do not use this product if you have abdominal pain or diarrhea. Consult a health care provider if you are pregnant or nursing. Discontinue use in the event of diarrhea or watery stools. Do not exceed recommended dose. Not for long-term use." 
Burdock is classified as able to be safely consumed when used appropriately. Given the lack of toxicity data and the reports of in-vitro uterine stimulant action, use of burdock during pregnancy and lactation should be avoided. Excessive doses may interfere with existing hypoglycemic therapy, presumably because the slow-burning starch would delay digestion and, therefore, the assimilation of any pharmaceutical.
German Chamomile: Classed as safe for use when used appropriately, although minor side effects have been recorded. Clients with sensitivity to asteraceae/compositae family should avoid it. It may also exacerbate symptoms in clients who are particularly susceptible, such as asthmatics. The coumarin constituent may interfere with anticoagulant therapy if used in excessive doses.  Newall, Anderson, and Phillipson recommend avoiding excessive use during pregnancy and lactation due to reputed effects on the menstrual cycle and uterotonic activity. They also state it is not recommended for teething babies but do not give a reference for this statement. Traditionally both chamomiles have been used for teething babies.
Roman Chamomile: Large doses of Chamaemelum nobile have been reported to cause vomiting and stomach irritation and the herb can cause skin reactions and other allergic reactions in people who have sensitivity to ragweed pollen. The sesquiterpene lactones may be the primary allergen, although sensitization occurs only rarely with the widely used German chamomile.  Excessive use during pregnancy and lactation should be avoided due to reputed abortifacient actions, its ability to affect the menstrual cycle, and the potential allergic effects. The coumarin constituent may interfere with anticoagulant therapy if used in excessive doses.  The Natural Standards Database (which you can access through the library, through the databases page) states: In a study of 588 pregnant Australian women, 36% of the women had taken herbal supplements during their current pregnancy, and 11% took chamomile. There have been no formal studies on the effects of chamomile on pregnant women. However, due to its theoretical properties as a uterine stimulant, abortifacient, and emmenagogue, most experts agree that excess ingestion of chamomile should be avoided during pregnancy. Roman chamomile has a class 2b safety rating from the American Herbal Products Association, advising against its use during pregnancy, because of its potential abortifacient effects when taken at high doses due to its action on uterine smooth muscle and tendency to induce menstruation.
Chickweed is classified as safe if used appropriately. The AHPA notes one alleged case of nitrate toxicity associated with chickweed; however, this may have been caused by harvesting from fields where synthetic fertilizers were used. This example illustrates the importance of gathering herbs from wild areas or organic farms.
Cleavers: Classified as safe to consume when used appropriately. There is some suggestion that diabetics should only use the juice with caution.  Due to the lack of toxicological and pharmacological data, use during pregnancy should be avoided. Note: Cleavers juice is a powerful diuretic and should not be used where there is a tendency towards diabetes, as it can increase the amount of sugar in the urine. Remember: Always use a demulcent herb for inflamed or painful conditions.
There have been two reports of human hepatotoxicity with ingestion of comfrey. Research has shown the pyrrolizidine alkaloids cause liver damage when injected under the skin of laboratory rats for periods of 18 weeks to two years. From these studies with the concentrated alkaloids, scientists speculated that regular users of comfrey could sustain liver damage by taking 2-mg or more of this herb every day over a period of two years. This is particularly of concern for young children. Comfrey root contains allantoin, a substance that speeds up the regeneration of damaged tissue both internally and externally. This agent stimulates the tissue growth of wounds; theoretically, if the wound is infected, this might result in the wound healing over and driving the infection deeper, as can happen with calendula Calendula officinalis. The pyrrolizidine alkaloid content has lead to the American Herbal Products Association (AHPA) classifying comfrey as being for topical use only and not to be used during pregnancy or nursing. They recommend limiting topical application to four to six weeks of daily use. The following cautionary statement is recommended for labeling products containing pyrrolizidine alkaloids: "For topical use only. Do not apply to broken or abraded skin. Do not use when nursing." However, the AHPA notes that due to the lower content of the alkaloid in the leaf and the absence of echimidine, the limitation to topical use may be excessively cautious for the leaf. Even given this lower alkaloid content, oral use for more than four to six weeks per year is discouraged. In small medicinal quantities as a tea, infusion, or cooked, the danger is minimal, as heat apparently inactivates the alkaloid. It is also quite safe to use topically as a poultice or fomentation, as the alkaloids are not absorbed through the skin. The AHPA warns against applying directly to broken or abraded skin, but percutaneous absorption of pyrrolizidine alkaloids is thought to be low. In the UK, licensed herbal products intended for oral use are not permitted to contain comfrey. Comfrey may be included in products intended for topical application provided it is restricted to less than 10 days of consecutive use. In 1993, the natural health industry in the United Kingdom voluntarily withdrew all products containing comfrey and relabeled them with warnings against ingestion. This followed a Food Safety Directive put out by the Committee on Toxicity of Chemicals in Food, part of the Ministry of Agriculture Fisheries and Food. It should be noted that the concentrated alkaloid extract would be considerably more potent than if the whole leaf or root was used. It is quite possible that comfrey contains substances that counteract the damaging effects of the alkaloid. It is very important when gathering comfrey to ensure accurate identification, as it is easy to confuse comfrey with other Symphytum species that contain echimidine. Echimidine is one of the most toxic of the pyrrolizidine alkaloids, and is not found in most samples of S. officinale. Apart from the two instances mentioned above, most reports of human hepatotoxicity have resulted from crop contamination with Cortalaria, Heliotropium, and Senecio species. There are some indications of carcinogenic activity in rats fed a diet supplemented with comfrey. However, other studies dispute this finding.
Dandelion: Leaf: None reported
Root: Do not use if you have blocked bile ducts, gallbladder inflammation, or intestinal blockage.
Do not use during pregnancy or nursing. Large doses can cause vomiting, diarrhea, spasms, and symptoms of paralysis. In the United States, it is regulated as an allowable flavoring agent in alcoholic beverages only. Elecampane may cause contact dermatitis, and may interfere with existing treatment for hypoglycemic and antihypertensive treatments.
Evening Primrose: Classed as safe for use when used appropriately by the American Herbal Products Association. Newall, Anderson, and Phillipson note that there is a potential for evening primrose to make manifest undiagnosed temporal lobe epilepsy particularly in schizophrenic patients and possibly those on epileptogenic drugs such as phenothiazines. 
Fennel can cause photo dermatitis, and excessive exposure to sunlight or ultraviolent light should be avoided. The German Commission E Monographs note that fennel can cause allergies and should not be used for prolonged periods in medicinal amounts without a professional consultation. Allergic cross-sensitivity is possible in people with allergies to carrot, celery, mugwort, or other Apiaceae family plants.
Feverfew: None known
Flaxseed: As with any mucilage preparation, it can affect the absorption of prescription medication. Do not exceed the recommended dose. Flaxseed contains a very small amount of linamarin, a cyanogenic glycoside, which has been considered a potential source of dietary hydrogen cyanide (HCN) poisoning in the past, although research that is more recent has shown that HCN is not readily absorbed from flaxseed.
A large dose will have a laxative and diuretic action. If used in excessive amounts, it can cause diarrhea and stomach aches. It should not be used for longer than approximately eight consecutive days without a break of at least 10 days, after which time the remedy can be repeated for a further eight days. When fumitory is taken over a prolonged period, it can slow down the circulatory system and induce sleepiness.
Garlic is generally considered non-toxic. It is classed as restricted for use during nursing. Garlic should be used with care in pregnancy. Uterine stimulation has been shown in animals, and it has a reputation as a potential abortifacient. While there are no experimental or clinical reports on adverse effects during pregnancy or lactation, high doses should be avoided. High doses can also act as a stomach irritant and cause liver and kidney damage, and topical application can produce blistering and dermatitis. Hyperglycemic activity and an increase in serum insulin were noted in diabetic rabbits fed garlic. High doses of garlic may interfere with existing hypoglycemic and anticoagulant therapies. High doses of garlic may enhance or increase the antithrombotic effects of anti-inflammatory drugs such as aspirin.
Ginger Zingiber officinale is classed as safe for appropriate use by the AHPA. The use of ginger during pregnancy is controversial. The American Herbal Products Association state it should not be used during pregnancy and people with gallstones should consult and practitioner before using ginger. The PDR for herbal medicine contraindicate ginger for morning sickness due to its cholagogue effect. The concern is due to preliminary evidence that ginger might affect fetal sex hormones, and an anecdotal report of spontaneous abortion during week 12 of pregnancy in a patient who used ginger for morning sickness. However, studies in pregnant women suggest that ginger can be used safely for morning sickness without harm to the fetus. The risk for major malformations in infants of women taking ginger does not appear to be higher than the baseline rate of 1% to 3%. As with any medication given during pregnancy, the potential benefit to risk must be weighed. Dosage and duration are particularly important if one chooses to use ginger during pregnancy. "Ginger use during pregnancy is being questioned due to a new report from the Finnish government. Finnish authorities are warning pregnant women not to consume ginger supplements, drinks, or teas. Ginger contains chemicals that are cytotoxicin vitro. The concern is that these chemicals MIGHT be harmful if consumed in large quantities. So far, no obvious problems have been seen in pregnant women taking ginger supplements in doses of about one gram daily. Advise women not to overdo it. More is not necessarily better. Also, consider recommending vitamin B6 (pyridoxine) first for morning sickness. Vitamin B6 12.5 - 25 mg three or four times daily is safe and often effective for mild nausea." [source [text annotation indicator] ] Due to its antiplatelet action, ginger could interact with anticoagulant and antiplatelet drugs. There is one case report of a 76-year-old woman with a stable international normalized ratio on phenprocoumon (a warfarin-related anticoagulant used in Europe) that increased to greater than 10 when she began consuming dried ginger and ginger tea. However, research in healthy people suggests that chronic ingestion of ginger has no effect on international normalized ratio, or the pharmacokinetics or pharmacodynamics of Warfarin. Some anticoagulant or antiplatelet drugs include aspirin, clopidogrel (Plavix), dalteparin (Fragmin), enoxaparin (Lovenox), heparin, ticlopidine (Ticlid), warfarin (Coumadin), and others. Ginger's ability to increase the release of insulin could result in a potential interaction with antidiabetes drugs and even cause hypoglycemia. Some antidiabetes drugs include glimepiride (Amaryl), glyburide (DiaBeta, Glynase PresTab, Micronase), insulin, metformin (Glucophage), pioglitazone (Actos), rosiglitazone (Avandia), and others. Since preliminary research shows ginger has a hypotensive and calcium channel blocking effects, it may potentially interact with calcium channel blockers. Calcium channel blockers include nifedipine (Adalat, Procardia), verapamil (Calan, Isoptin, Verelan), diltiazem (Cardizem), isradipine (DynaCirc), felodipine (Plendil), amlodipine (Norvasc), and others.
Horehound should not be used during pregnancy. The plant juice can cause contact dermatitis. Excessive doses of horehound will cause nausea and diarrhea and should be avoided. Large doses may also cause arrhythmia. Yet, despite these precautions, The German Commission E Monographs list no known contraindications or side effects.
Do not use hyssop during pregnancy, as it is an emmenagogue and uterine stimulant. Hyssop oil (possibly the constituents pinocamphone and isopinocamphone) has been shown to cause central nervous system convulsions and death in experimental rats and is associated with tonic-clonic convulsions in adults and children. Do not use for children at all and closely follow dosage instructions for adults. Do not use the essential oil orally. Use preparations from the herb instead. The essential oil has a much lower therapeutic margin, with reports that 10 to 20 drops have caused tonic-clonic convulsions in two adults and just two to three drops over several days have caused them in one child.
Juniper is contraindicated during pregnancy as it is a reported abortifacient and affects the menstrual cycle. Do not use during nursing. It should not be used for more than four to six weeks without a break. . Prolonged or excessive use can result in renal damage. Symptoms of kidney damage include pain in the kidneys that usually is felt in the lower back, an increased urge to urinate, and the presence of blood or protein in the urine that is also known as hematuria and albuminuria. It is also contraindicated for inflammatory kidney disease, as it is a stimulating diuretic. Canadian regulations prohibit juniper in non-medicinal oral use products. Prolonged use may lead to hypokalemia. External application of the essential oil may cause dermal irritation, although it is possible that reports of irritation were caused by confusion between J. communis and J. savin. Juniper may potentiate hypoglycemic and diuretic therapies. The essential oil can be sensitizing if skin is sensitive or damaged, has a toxic rating of II and a skin patch test is required.
Licorice is relatively safe, but excessive doses can deplete the body of potassium and cause retention of sodium. Licorice is more effective when taken before food. Large doses over a prolonged period should be avoided and it is wise to ensure that potassium intake is increased. If consumed in therapeutic doses over a prolonged period, it has also been known to cause reversible potassium depletion and sodium depletion, which can cause symptoms of hypertension, edema, electrolyte imbalance, headache, and vertigo. DGL is usually free of these effects. Licorice is contraindicated for diabetes, hypertension (refer to the research discussed previously that shows that an alcoholic extract may be supportive for these conditions), liver disorders, severe kidney insufficiency, hypertension, cardiovascular disease or hypoglycemia, and hypokalemia. Licorice may enhance or increase potassium depletion of thiazide diuretics and stimulant laxatives, cardiac glycosides, and cortisol. It should not be used during pregnancy or nursing. Licorice may interfere with existing hypoglycemic therapy and hormonal therapy, as estrogen and antiestrogenic activity have been documented in vivo.
Marshmallow is classed safe for use when used appropriately. (The Commission E monographs state that absorption of other drugs taken simultaneously may be delayed, but they do not cite a reference. The high level of mucilage is most likely the cause for any delayed absorption.)
Motherwort: The German Commission E Monograph lists no known side effects or interactions with other drugs. The American Herbal Products Association indicates motherwort is contraindicated for use during pregnancy due to its emmenagogue and uterine stimulant actions. One report noted that a dose over 3.0-g of powdered extract might cause diarrhea, uterine bleeding, and stomach irritation. Newall, Anderson, and Phillipson note that the leaves may cause contact dermatitis and the oil may cause photosensitization. There is also indication the cardiac glycosides may interfere with existing therapy for a cardiac disorder.
Mouse ear can cause an allergic reaction in individuals sensitive to the Asteraceae/Compositae family. Members of this family include ragweed, chrysanthemums, marigolds, daisies, and many other herbs.
Mullein is classed as safe for consumption when used appropriately.
Do not take parsley during pregnancy and lactation in amounts exceeding that normally consumed in food. There is a report of myristicin crossing the placenta and leading to fetal tachycardia. It is also contraindicated where there is inflammatory kidney disease. The essential oil must not be used in large doses. The high levels of apiol and myristicin can cause deafness, giddiness, lowering of the blood pressure, slowing of the pulse, paralysis, and fatty degeneration of the liver and kidneys.
Plantain is classed as able to be safely consumed when used appropriately. The thioglucoside content releases an irritant principle on enzymatic hydrolysis (the catalytic decomposition of a chemical compound by reaction with water). This may be responsible for the reports of contact sensitization to plantain. There are documented reports of in-vitro uterotonic activity. Therefore, excessive use should be avoided during pregnancy. Overuse can also have a laxative effect.
Pumpkin seeds are non-toxic in higher doses.
Red clover should not be used during pregnancy due to the isoflavone content. Large quantities of red clover may interfere with anticoagulant and hormonal therapies, due to the coumarin and isoflavonoid constituents. Researchers at the University of Ottawa have shown there is some evidence that red clover may utilize the P450 cytochrome metabolic pathway in the body, which could indicate potential herb drug interactions. Pharmaceuticals that use this pathway include antiretrovirals and oral contraceptives.
Red Raspberry: Classified as safe for consumption when used appropriately. Some uteroactivity has been documented, both reducing and initiating uterine contractions. In view of this, it should not be used when there is a history of miscarriage unless under supervision of a health care practitioner. Toxic constituents are borneol camphor and pinene. Despite the recommendation of rosemary for asthma, exercise caution if a client has chronic asthma, epilepsy, or hypertension. Rosemary is an effective antispasmodic but camphor in excessive doses (5-ml per kilo of body weight) can aggravate asthma and epilepsy. Always follow dosage carefully for the essential oil in particular. It can regulate low blood pressure, however. A skin patch test is recommended prior to topical use. It is contraindicated in the first trimester of pregnancy and should not be administered to babies or children under the age of four. It can antidote homeopathic remedies if stored with them or administered at the same time. Toxic rating is II and skin patch test is required.
Sage is approved for food use in the United States when used orally in amounts commonly found in foods. Do not use sage during lactation, as it will dry up the milk supply. Because of this, it is useful for a mother who is weaning an older baby. It is contraindicated for use during pregnancy. The essential oil is contraindicated for long term use and do not exceed recommended dose. Camphor and thujone, two constituents found in sage, are toxic in large doses or in moderate amounts taken over a period, as they are cumulative. The essential oil is reported to be a moderate skin irritant.
Use with caution if there is a known allergy/hypersensitivity to shepherd's purse, its constituents, or members of the Brassicaceae family. Use cautiously in patients taking sedatives, diuretics, cardioactive, hypertensive, hypotensive, or thyroid drugs, herbs, or supplements. Based on anecdotal reports, shepherd's purse may interfere with or enhance the effects of these types of agents. Use cautiously in patients with kidney stones, according to secondary sources
The AHPA lists slippery elm as safe for use when used appropriately.
Sorrel leaves contain 7-15% tannins. In general, plants that contain more than 10% tannins might cause stomach upsets, renal damage, hepatic necrosis, and increased risk of esophageal and nasal cancers. Sorrel also contains .3% oxalate (oxalic acid). Oxalic acid combines with calcium to form calcium oxalate crystals, which may develop in the kidneys, blood vessels, heart, lung, and liver, leading to hypocalcemia and renal lesions. Oxalate crystals damage mucosal tissue and cause severe irritation.
Spearmint is classed as generally safe for use when used appropriately. Essential oil of spearmint is potent and doses in excess of the recommended dose can cause gastro-intestinal irritation and depression of the central nervous system. Recently there have been some reports that the use of some herbal teas can negatively affect male reproductive function. A study in the journal Urology in 2004 found that spearmint increased follicle stimulating hormone and luteinizing hormone and decreased total testosterone levels in male rats. The study also found developmental effects on the sperm, the degree of which varied in relation to dose. So for couples having fertility issues, it might be better for the male not to drink spearmint or peppermint tea. 
Sweet basil is contraindicated for use while pregnant, breast-feeding, and with infants or toddlers. Do not use for extended periods in doses higher than that used as a spice. Do not use the essential oil during pregnancy or nursing. It contains up to 85% estragole (methyl chavicol), which can produce liver tumors in mice. The constituent, xanthomicrol, can have cytotoxic and antineoplastic activities. Orally, basil is known to cause hypoglycemia.
Thyme is classed as safe for use when used appropriately by the American Herbal Products Association. Thyme is traditionally reputed to affect the menstrual cycle, therefore amounts greater than that usually used in food should not be taken during pregnancy or lactation. Thyme essential oil has a low therapeutic margin and should never be used orally or topically without dilution. Thyme essential oil is a dermal and mucus membrane irritant.
As with all herbs high in tannin, uva ursi should not be used for long periods as it may cause liver damage. Cold water preparations will extract less tannin and most of the allantoin. It is contraindicated for pregnancy, kidney disorders, irritated digestive conditions, acidic urine, or in conjunction with remedies that cause acidic urine. Clients should avoid acidic juices and fruits. It should not be used for more than one month in therapeutic quantities without consulting a practitioner. Canadian regulations do not allow use of uva ursi in non-medicinal oral use products.
Watercress taken in large amounts can cause gastrointestinal irritation, and excessive or prolonged use might cause kidney damage.
Classed as safe for consumption when used appropriately. There have been isolated reports of stomach irritation and one case of witch hazel tannins causing liver damage. The volatile oil contains safrole, which is a known carcinogen, but in amounts considered too low to be problematic.
The Commission E Monographs list no known side effects for yarrow, and no known drug interactions.However, the AHPA contraindicates yarrow for pregnancy due to its emmenagogue and uterine stimulant activity. For this reason it should also be avoided while nursing. People who have allergies to members of the asteraceae family should either avoid its use or immediately cease use should allergic reactions such as itching and inflammatory changes to the skin appear. Yarrow essential oil contains trace amounts of thujone, a toxic ketone. Theoretically, using other thujone containing herbs along with yarrow could increase the risk of thujone toxicity. Other herbs that contain thujone include oak moss, oriental arborvitae, sage, tansy, thuja (cedar), tree moss, and wormwood. Avoid using with yarrow. United States Federal Regulations require that food or beverage products containing yarrow be thujone free. Excessive doses may interfere with anticoagulant, hypo and hypertensive therapies, and have sedative and diuretic effects. The essential oil has a toxic rating of II and a skin patch test is required. The toxic constituents are camphor and thujone. Do not use the oil in cases of asthma.
Yellow dock: Individuals with a history of kidney stones should use yellow dock cautiously. Yellow dock is a stimulant laxative; therefore, it should not be taken where there is intestinal obstruction, during pregnancy, or lactation.