A handbook on some officinal plants toxicity

Even though people often think that “natural means safe”, officinal herbs too have their side-effects and their toxicity. Particularly, it’s necessary to be careful about their interaction with drugs taken at the same time, and patient’s potential pathologies must be taken into consideration. Thus, on the one hand herbs can treat a disorder but, on the other hand they can also cause complications.
Patients allergic to aspirin, for example, must not take compounds based on Willow, Poplar and Birch, just because they contain acetylsalicylic acid.
Therefore always get first medical advice on the suitability of a phitoterapic treatment in relation to your pathologies and, if not possible, be always careful about the general indications of this handbook before using a recipe you think may be suitable for you.



Let’s pass to analyse the side-effects of the most widely known medicinal plants.



SORREL AND RUMEX ACETOSELLA are not recommended for people suffering from gastric or liver diseases, because they contain calcium oxalate; they are also not recommended for people suffering from calcium oxalate nephrolithiasis.
YARROW could cause allergic reactions in people sensitive to Composites; if overused, it may cause skin rashes due to the exposure to sun rays. It’s contraindicated in children younger than 2 years old.
GARLIC preparations should be carefully used by people suffering from gastritis or having any other form of gastrointestinal irritation or inflammation: disulfide compounds contained in garlic can potentially be irritating for the mucosa.
It’s better not to use it before a surgical intervention because of its antiplatelet activity. Since it is reported to have caused allergic reactions (such as contact dermatitis, hives, ecc), it’s not recommended in allergic subjects as well as in people suffering from anaemia and hyperthyroidism.
BAY (Laurus) can cause allergies or contact dermatitis in chefs, dentists or people working in the pharmaceutical sector.
ALOE VERA for topic use can cause acute dermatitis in hypersensitive people. It’s contraindicated in children younger than 12 years, in case of diverticulosis, in people with intestinal occlusion or subocclusion, in people suffering from haemorrhoids or perianal fistulas and in patients having inflammations to small pelvis organs.
ANGELICA is not recommended during sun exposure (because it contains furocoumarines) and is contraindicated for people affected by gastric ulcer or diabetes disorders.
ANISE, although generally well-tolerated, can sometimes cause breathing and gastrointestinal allergic reactions; it’s contraindicated in subjects sensitive to anethole.
BITTER ORANGE essential oil, that is Neroli essential oil, is phototoxic and distilled oil can cause dermatitis or increase photosensitivity in subjects already very sensitive.
ARNICA is contraindicated for topic use if the skin is not completely unbroken, since small cuts can absorbe arnicina and cause nausea, vomiting, diarrhoea and hallucinations.
DEVIL’S CLAW is contraindicated in people suffering from gastric or duodenal ulcer and from biliary lithiasis, since it causes nausea and gastric heartburn.
ASPARAGUS is contraindicated in case of glomerulonephritis, kidney failure and kidney lithiasis.
ASAFOETIDA should not be given to children since it is reported to have caused a case of methemoglobinemia in a newborn whose mother had taken this compound to heal a colic attack.
OATS can cause allergic reactions and can not be taken in case of gluten intolerance. It’s not recommended for hyperthyroidism.
BALSAM OF PERU can cause dermatitis.
BASIL is not recommended in people suffering from high blood pressure, because it can increase arterial pressure, and in children.
BERGAMOT can cause photosensitivity reactions and is not recommended for sun exposure.
BIRCH is not recommended in cases of oedemas caused by heart or kidney failure because of its diuretic effect.
HAWTHORN must be carefully used in subjects affected by bradycardia, sinoatrial or atrioventricular blocks.
BOLDO is not recommended in case of kidney disease or severe liver problems and in case of biliary ways occlusion.
BORAGE OIL should not be used in epileptic patients or people suffering from dissociative disorder.
CHAMOMILE is not recommended in people hypersensitive to plants belonging to the Composites family. It could also cause allergies in asthmatic people and must not be used for newborns. It’s possible to have contact dermatitis. Chamomile essential oil can have cytotoxic, irritating and sensitive effects.
COMMON NASTURTIUM is not recommended in children, in people suffering from gastritis, intestinal ulcer and kidney disorders.
ARTICHOKE is not recommended in people suffering from biliary lithiasis. It’s intake can cause contact dermatitis.
MOTHERWORT is not recommended for hypotensive or hyperthyroid people.
MILK THISTLE, because of tyramine content, is not recommended for hypertensive people.
It can cause insomnia. Do not take it in the night. Carefully give it to people suffering from biliary calculi and biliary ways occlusion.
CARROT, because of psoralens content, can cause phototoxic reactions. It can alter arterial pressure.
CASCARA, and other drugs with anthraquinones (Rhubarb, Senna, Buckthorn, ecc) is contraindicated for children younger then 10 years, in case of intestinal diverticulosis, in patients with intestinal occlusion, haemorrhoids and perianal fistulas, in women suffering from low basin organ inflammation. Preparations based on Cascara are contraindicated in all cases of intestinal inflammation (ulcerative colitis, appendicitis, ecc…) and in undiagnosed abdominal pains. It’s not recommended to take it for a long time since it could worsen intestinal atony.
NOTCH is suspected to cause photosensibilization. It’s not recommended in children younger than 2 years. Topic use can cause dermatitis or contact allergies. It can stimulate thyroid functioning. Therefore it must be cautiously given to patients affected by hyperthyroidism. High doses can cause headache.
CHINA high doses can cause headache, abdominal pains, deafness, nausea, vomiting, visual disorders. It must not be given to subjects suffering from gastritis, ulcers or blood coagulation and heart rate disorders (because of quinidine action).
CLOVES, the essential oil is not recommended for skin applications. It must be cautiously given to subjects affected by blood coagulation disorders.
BLACK COHOSH over consumption can cause nausea, vomiting, dizziness. It has a digitalis-like action. Therefore, it’s dangerous for people suffering from heart disorders and people who are undergoing treatments based on digitalics and atropine.
ONION, especially bulbs, can cause irritation because of the presence of propenesulfenic acid. The oil has an antithyroid action and is not recommended for hypochlorhydric individuals.
COKE toxicity is due especially to the presence of caffeine. It must be cautiously given and is not recommended for people suffering from high blood pressure or peptic ulcer.
CURCUMA, for its choleretic and cholagogue action, is not recommended in people suffering from biliary lithiasis or biliary ways occlusion. Moreover, preparations based on curcuma can increase the symptoms of the disease in some people affected by gastrointestinal ulcer or gastric hypersecretion.
SUNDEW must be cautiously given to babies since high doses can cause irritations of gastric mucosa. It’s not recommended in people suffering from ulcer or other gastric disorders.
GARCINIA (Garcinia cambogia); fam.: Ipericaee.
Side-effects and contraindications – do not take during pregnancy.
GREAT YELLOW GENTIAN (Gentiana lutea); fam.: Genzianacee.
Side-effects and contraindications- it’s not recommended for people suffering from gastric disorders, ulcer and high blood pressure. Do not give during pregnancy and breastfeeding.
JUNIPER (Juniperus communis); fam.: Cupressacee.
Side-effects and contraindications: it must be cautiously used for patients suffering from kidney or gastrointestinal disorders: the essential oil, which can also cause hematuria, if applied to the skin, has a vesicant effect. It must not be given during pregnancy because it can cause miscarriage. 
GINKGO BILOBA (Ginkgo biloba); fam.: Ginkgoacee.
Side effect and contraindications: the ingestion of its fruits can cause mucosa inflammation; excessive doses can cause dermatitis, headache, vomiting and diarrhoea. It reduces coagulation time. Be careful with the contemporary use of anticoagulant drugs since it can increase their effects. The pairing of aspirin and ginkgo can be particularly dangerous, since the latter contains ginkgolide B among its active constituents, a powerful inhibitor of the PAF (Platelet-Activating Factor). You must consider however, that these haemorrhagic complications can occur also after a brief administration of ginkgo and that the risk increases with the contemporary assumption of aspirin which is another powerful antiplatelet drug.
GINSENG (Panax ginseng); fam.: Araliacee.
Side-effects and contraindications- it could increase the MAO action. Ginseng is contraindicated in haemorrhagic conditions and in coronary thrombosis critical stages. Ginseng, moreover, should not be given to hysterics, anxious people and all those who are taking stimulating drugs, antipsychotic drugs and hormones. It’s contraindicated for people suffering from high blood pressure. In case of prolonged administration there can be side-effects which are similar to those deriving from an overdose of corticosteroids. Over consumption can cause various disorders such as: insomnia, tremor, headache, itch, heart palpitations; remember the ginseng abuse syndrome. It’s not recommended during pregnancy.
GUAJACO (Guaiaco officinale); fam.: Zygophyllacee.
Side-effects and contraindications – It’s not recommended in pregnancy and breastfeeding and in all the people who suffer from any kind of allergy. The plant resin can cause contact dermatitis.
GUARANA (Paullinia cupana); fam.: Sapindacee.
Side-effects and contraindications – it’s not recommended in people suffering from high blood pressure or cardiovascular diseases.
Since it contains caffeine, it must be cautiously given; it is not recommended for people suffering from high blood pressure, gastric disorders or peptic ulcer. Be careful about the contemporary use of coffee, tea and drugs containing caffeine.
Drugs containing caffeine, used for a long time during pregnancy, can cause fetal malformations.
GUGGUL (Commiphora mukul); fam.: Burseraceae.
Side-effects and contraindications – people who are following an antiplatelet therapy or suffering from gastro-intestinal disorders, such as duodenal or gastric ulcers, must take it with caution. Guggul can reduce plasmatic concentration of drugs such as propanolol and diltiazem. Do not take during pregnancy.
GYMNEMA (Gymnema silvestre); fam.: Asclepiadacee.
Side-effects and contraindications – Do not give to diabetics who are taking oral antidiabetic drugs. Do not take during pregnancy.
GOLDENSEAL (Hydrastis canadensis); fam.: Berberidacee.
Side-effects and contraindications – It contains berberine and, together with other plants, such as Berberis vulgaris, is thought to be very hepatotoxic. It’s not recommended during pregnancy, for people suffering from high blood pressure and cardiovascular diseases.
IPECACUANHA (Cephaelis ipecacuanha); fam.: Rubiacee.
Side-effects and contraindications – An overdose of normal preparations of this plant can cause uncontrollable vomiting and diarrhoea followed by a shock that in some cases can lead to death. It’s a plant to use very cautiously since it contains emetine. Do not give to babies, during pregnancy or to people suffering from cardiovascular diseases.
HYPERICUM (Hypericum perforatum); fam.: Ipericacee.
Side-effects and contraindications – it’s not recommended for chronic depressed people and people suffering from bipolar disorder. The hypericin contained in the plant can be photosensibilizing. Hypericum, because of its action similar to MAO inhibitors, which are drugs used to treat depression, should not be associated to foods containing tyramine and also to milk thistle. (Toxicological effects of Medicinal plants, part II) ( R. Carbone )
HORSE CHESTNUT (Aesculus hippocastanum); fam.: Ippocastanacee.
Side-effects and contraindications – it can interfere with the action of coumarins. It could increase antiplatelet drugs effects. To use carefully for internal use, it’s not recommended in case of kidney failure. Horse chestnut intoxication gives gastrointestinal symptoms (nausea, vomiting, diarrhoea). Later on it could cause a haemorrhagic syndrome which is difficult to treat. It’s not recommended during pregnancy or breastfeeding.
ISPAGHUL (Plantago ovata ); fam.: Lamiacee.
Side-effects and contraindications – it’s a plant to take with a lot of water or other liquids, it increases intestinal content and stimulates peristalsis; it must not be given to patients suffering from intestinal disorders. The consumption of dried seeds can cause gastrointestinal irritation, constipation and mechanical obstruction. Ispaghul powder is a respiratory allergen and, after seed consumption, can cause anaphylactic shock.
KAWA KAWA (Piper methysticum); fam.: Piperacee.
Side-effects and contraindications – if you are under the effect of kawa kawa, motor vehicle driving is not recommended, especially heavy ones, which require a high level of attention. It must not be given during pregnancy and breastfeeding, and in case of depressive conditions. Prolonged use is not recommended since it could cause hair, skin and nails depigmentation. It must be considered that the use of this plant could increase alcohol, barbiturates and other psychopharmaceutical substances effects. It’s also possible to have pupil dilatation and difficulties in vision-movement coordination.
LAVENDER (Lavandula officinalis); fam.: Labiate.
Side-effects and contraindications - High doses can cause sleepiness.
LIQUORICE(Glycyrrhiza glabra); fam.: Papilionacee.
Side-effects and contraindications – Glycyrrhizin and glycerine contained in the plant have mineral corticoid effects. Liquorice must not be taken in high doses or for a prolonged period since it can increase blood pressure, oedemas, hypokalemia and hyponatremia, heart disorders. Be careful about contemporary use of liquorice and drugs containing digoxin. It’s better not to give it to people suffering from diabetes, high blood pressure, kidney failure, cirrhosis of the liver, cholestatic liver diseases. Do not overdose during pregnancy and breastfeeding.
HOP (Humulus luppulus); fam.: Cannabinacee.
Side-effects and contraindications – It should not be administered during pregnancy or to epileptics; high doses cause nausea, headache and dizziness. Since it contains estrogenic substances, it could decrease libido. Strong respiratory allergies have been found after the handling of flowers gathered in cones. Hop should not be given to people suffering from depression. Avoid the contemporary use of alcohol and sedative drugs. Do not use during pregnancy or breastfeeding.
MARJORAM (Origanum majorana); fam.: Lamiacee.
Side-effects and contraindications – The essential oil is not recommended during pregnancy. High doses can cause hematuria.
MAIZE (Zea mais); fam.: Poacee.
Side-effects and contraindications – The abuse or a prolonged therapy can cause gastro-intestinal symptoms (vomiting and diarrhoea). It could interfere with a contemporary hypoglycaemic therapy. Allergic reactions, including contact dermatitis and hives have been found. Avoid abuses during pregnancy and breastfeeding.
HOREHOUND (Marrubium vulgare); fam.: Labiate.
Side-effects and contraindications – The plant’s juice could cause dermatitis. It’s contraindicated during pregnancy and breast feeding.
MELALEUCA (Melaleuca alternifolia); fam.: Myrtacee.
Side-effects and contraindications – An intoxication case of a 17 years old guy who had taken 10 ml of essential oil is reported. He showed ataxia and drowsiness symptoms.
SWEET CLOVER (Melilotus officinalis); fam.: Fabacee.
Side-effects and contraindications – It must not be given to patients who suffer from blood coagulation disorders or take antiplatelet drugs such as for example Warfarin. A continuous use can cause hepatotoxic phenomena; there can be also gastro-intestinal disorders.
LEMON BALM (Melissa officinalis); fam.: Labiate.
Side-effects and contraindications – It’s thought, after high doses administration, to have antithyroid effect, through the inhibition of TSH secretion (thyroid hormone), quite surely because it contains rosmarinic acid. The latter is contained also in other plants such as rosemary for example. The essential oil is not recommended since two grams of it cause low blood pressure, bradycardia breathing difficulty, numbness and sleepiness.
PEPPERMINT (Mentha piperita); fam.: Labiate.
Side-effects and contraindications – It’s not recommended for children; the essential oil can be irritating and cause allergic reactions. High doses taken at night can cause sleep disorders. It interferes with homeopathic drugs by hindering their action and is contraindicated during breast feeding. Recurring muscle pains have been put down to internal use of the essential oil; bradycardia has been reported in people smoking menthol cigarettes while overconsumption of sweets containing peppermint aromas has caused fibrillation. It’s contraindicated for biliary lithiasis.
BLACK BLUEBERRY (Vaccinium myrtillus); fam.: Ericacee.
Side-effects and contraindications – Prolonged use and the abuse of therapies based on its leaves can cause methemoglobin formation.
RED BLUEBERRY (Vaccinium vitis-idaea); fam.: Ericacee.
Side-effects and contraindications – Be careful about overdoses. It can cause jaundice.
NIAOULI (Melaleuca viridiflora); fam.: Myrtacee.
Side-effects and contraindications – The essential oil must not be used externally for babies. Oral use of the essential oil can increase some drugs effectiveness if they are given at the same time.
OENOTHERA (Oenothera biennis); fam.: Onagracee.
Side-effects and contraindications – The oil could cause undiagnosed temporal lobe epilepsy. Sometimes gastrointestinal side-effects and headache are reported. It’s not recommended in patients suffering from temporal lobe epilepsy and in those treated with phenothiazines.
NETTLE (Urtica dioica); fam.: Urticaceae.
Side-effects and contraindications - Infusions can cause gastric irritation. Moreover it can cause skin itch, oedema and oliguria. It can interfere with a contemporary hypotensive or antidiabetic therapy; there can also be an enhancement of depressive drugs on SNC. It’s not recommended for people suffering from kidney failure, during pregnancy and high doses should not be used during breastfeeding.
PAPAYA (Carica papaya); fam.: Caricaceae.
Side-effects and contraindications – Fresh latex, in contact with eyes, can cause inflammations; skin contact can cause irritations and dermatitis.
PELLITORY OF THE WALL (Parietaria officinalis); fam.: Urticaceae.
Side-effects and contraindications – Asthmatic reactions and allergic rhinitis (hay fever).
PASSION FLOWER (Passiflora incarnata); fam.: Passifloraceae.
Side-effects and contraindications – Overdoses of this plant could enhance MAO inhibitors action of antihypertensive drugs. It’s not recommended during pregnancy. Overdose can cause headache.
HOT PEPPER (Capsicum annuum); fam.: Solanacee.
Side-effects and contraindications – Cases of contact dermatitis with paprika are reported; the topic and prolonged use of this ointment, together with dermatitis, could also cause vesicles and ulcers. It’s advisable not to abuse hot pepper for internal use since, strong doses, can be harmful for kidneys and cause gastritis, colon inflammations and constipation. It can interfere with MAO inhibitors.
PLANTAIN (Plantago major); fam.: Plantaginacee.
Side-effects and contraindications – It may cause contact dermatitis; high doses have a laxative effect. Moreover, it could have hypotensive effect. Do not abuse it during pregnancy.
PINE (Pinus sylvestris); fam.: Pinacee.
Side-effects and contraindications – The essential oil should not be applied by people having any type of skin allergy. It can cause convulsive crisis.
PARSLEY (Petroselinum sativum); fam.: Apiacee.
Side-effects and contraindications – The plant and its seeds are toxic: intoxication symptoms are haemolysis, liver-kidney damage, significant haemorrhages (low blood pressure, collapse, coma). It’s a haemolytic poison causing liver-kidney and neuro-toxic damage, since apiol acts on membrana lipids causing haemolysis through red corpuscles. The poison acts on hepathocyses determining fat degeneration of liver, on kidney cells with necrosis, but also on nervous cells causing degeneration of cornu anterius and peripheral nerves demyelisation. The toxicological pattern is characterized by a haemolytic and discoagulation syndrome with liver-kidney and neuro-toxic damage. Normal use of parsley in cooking does not cause any problem.
PROPOLS
Side-effects and contraindications – There have been several important allergic reactions (acute asthma attacks, erythema, oedema) to propolis, a product gathered by bees which contains many resins and essential oils, frequently used against airways inflammations and flu disorders.
Propoli allergenic properties are widely reported in literature (Callejo et al., 2001; Lombardi et al., 2003). This product is therefore absolutely contraindicated for allergic patients. What is surprising is the wide commercialization of propolis throat spray often recommended for kids too, a population for which allergic pathologies are becoming a very serious problem.
BLADDERWRACK (Fucus vesiculosus); fam.: Fucacee.
Side-effects and contraindications - It can worsen a pre-existing acne; moreover, it has been associated with acneiform eruptions. It must be avoided by hyperthyroid subjects.
RHUBARB (Rheum officinale, Rheum palmatum); fam.: Polygonacee.
Side-effects and contraindications – Besides containing anthraquinones, rhubarb, like sorrel, acetosella and spinach, it contains oxalates (in the root stock and the leave) under the form of oxalate, potassium and calcium acid. See anthraquinone drugs.
HORSERADISH (Armoracia rusticana); fam.: Crucifere.
Side-effects and contraindications – Its abuse can cause vomiting and allergic reactions. Horseradish should not be administered to patients suffering from gastritis and ulcer or in people affected by thyroid diseases. Do not prescribe during pregnancy or breastfeeding. Essential oil use is not recommended.
ROSEMARY (Rosmarinus officinalis); fam.: Labiate.
Side-effects and contraindications – Its abuse can cause convulsions and miscarriage in pregnant women. The essential oil must be cautiously used. High doses can cause convulsions; it’s phototoxic; it could cause dermatitis and erythema in hypersensitive people.
BUTCHER’S BROOM(Ruscus aculeatus); fam.: Liliacee.
Side-effects and contraindications – It should not be given to people suffering from high blood pressure; overdose has gastrointestinal symptoms (vomiting and diarrhoea).
RUE (Ruta graveolens); fam.: Rutacee.
Side-effects and contraindications – High doses can cause miscarriage; symptoms can be gastrointestinal pains, uterine haemorrhage and skin sensibilization.
WILLOW (Salix alba); fam.: Salicaceae.
Side-effects and contraindications – Do not take during pregnancy and in case of gastrointestinal disorders such as duodenal or gastric ulcers, oesophageal (reflux oesophagitis), ulcerative colitis, spastic colitis, diverticulosis, diverticulitis. Do not take in case of allergy to acetylsalicylic acid (aspirin). Do not take in case of contemporary antiplatelet therapy.
Note: Salicilin action has been tested in clinical trials with 60-120 mg/day doses of 15% salicin
SAW PALMETTO(Serenoa repens); fam.: Salicaceae.
Side-effects and contraindications - Instructions: Do not take during pregnancy.
MILK THISTLE (phytocomplex of flavonolignans extracts from milk thistle - Silybum marianum)
Side-effects and contraindications – This product, available also in drugs, is used as hepatoprotector and is usually well tolerated. The reported case of tachyarrhythmia and high blood pressure caused by milk thistle seemed quite singular. It was tested also with rechallange (galenic based on silimarina). This episode is maybe due to idiosyncrasy and it’s interesting for its reaction unreported in literature. The warning came from hospital doctor.
SOYA BEAN (Glycine soja); fam.: Fabaceae.
Side-effects and contraindications – Do not take during pregnancy. It can interfere with hormone substitute therapy followed during menopause.
DANDELION (Taraxacum officinale); fam.: Asteraceae (Composite).
Side-effects and contraindications – Do not take during pregnancy.
GREEN TEA(Camelia sinensis) fam.: Theaceae.
Side-effects and contraindications – Do not take during pregnancy.
UNCARIA (Uncaria tormentosa) fam.: Rubiaceae.
Side-effects and contraindications – Do not take during pregnancy.
BEARBERRY (Arctostaphylos uva ursi) fam.: Ericaeae.
Side-effects and contraindications – Do not take during pregnancy and do not give to people suffering from duodenal or gastric ulcers
GRAPE VINE (Vitis vinifera) fam.: Vitaceae.
Side-effects and contraindications – Do not take during pregnancy.

taken from an article written by R.Carbone on the magazine "Cahiers de Biotherapie" n°4 of 2006

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