Avoid if known allergy/hypersensitivity to mistletoe or to any of its constituents.

Anaphylactic reactions (life threatening, shock) have been described after injections of mistletoe.

Mistletoe is contraindicated in patients with protein hypersensitivity and/or chronic progressive infections (e.g. tuberculosis). Avoid use of mistletoe in patients with acute, highly febrile, inflammatory disease.

Most clinical trials were performed with unfractionated extracts, which contain numerous components, and it is difficult to ascribe adverse effects to any component of the mistletoe extracts. Most of the injected administrations of mistletoe may be accompanied by mild manifestations of similar side effects, most of them transient.

The most common reactions reported are erythema (reddening of the skin) and hyperemia (increased blood in an organ). Use of Iscador-M® has resulted in grade 3-4 toxicities (e.g. anorexia, general malaise, depressive moods, fever, and local skin inflammation at the site of injection). Other side effects observed have includes drug related fever, erythema at injection site and pain at the site of injection. No drug related discontinuation or toxic deaths occurred. Flu-like symptoms and transient exacerbations of gingivitis, fever, and eosinophilia have been reported.

Avoid use of mistletoe with cardiovascular disease, as many adverse effects are possible.

Dermatologic (skin) adverse effects may include burning sensation, indurations, pruritis, swelling, urticaria, vesiculitis, erythema, irritation at injection site, or allergic reactions like delayed hypersensitivity.

Avoid use of mistletoe in active/uncontrolled hyperthyroid patients. The manufacturer of Isorel®, Novipharm, notes that mistletoe may additionally activate the patient's already accelerated metabolism and cause over-stimulation, thus worsening the patient's status. Also use cautiously in diabetics, insulin levels may be altered.

Congested intestine, diarrhea, gastroenteritis, nausea, vomiting have been reported after mistletoe use. Moderate to mild flu-like symptoms, transient exacerbation of gingivitis and fever were observed in some patients with subcutaneous administration of mistletoe preparations. Hepatitis has been reported due to ingestion of herbal tablets containing mistletoe and other plant extracts. Elevations of liver enzymes have been reported with high doses of mistletoe.

High urinary frequency/nocturia has been observed. Coma, delirium, fatigue, hallucinations, headaches, pain (generalized, bone, joint), abnormal blood cell counts, pancreas and kidney damage have been reported along with seizures, and sleeplessness. In one clinical study muscle contracture, and muscular pain were reported.

Use cautiously in glaucoma patients or in those on cholinergics. Mydriasis and myosis/myalgia has been reported in clinical study after mistletoe administration. One report exists of eye irritation after ingestion of mistletoe.

Avoid use of mistletoe in pregnancy and breast-feeding due to the potential uterine stimulant activity of mistletoe.

Traditionally, tea has been made with mistletoe leaves, hawthorn leaves and flowers, and lemon balm leaves in equal parts. Two cups daily has been prepared by infusing 2 teaspoons of the mixture for five to ten minutes. Cold water infusions, dried aqueous extracts and fluid extracts (1:1 in 25% alcohol) have been taken by mouth.

Mistletoe has been studied in multiple injectable regimens (intravenous, subcutaneous, intrapleural), and given by a healthcare provider in a controlled setting. Sometimes therapy includes an induction phase and a maintenance phase. Mistletoe should only be given by a qualified health care professional. No standard dose can be recommended at this time. Further research is needed as there are many potential side effects and interactions.

Mistletoe has been studied in children for respiratory infections. Further research is needed before a recommendation can be made.

Mistletoe may increase the effects of blood pressure lowering medications or have other more serious adverse effects on the heart. Busulphan and mistletoe extract (Helixor®) has been reported to cause organ fibrosis and death.

Using of mistletoe with CNS depressants may enhance sedative effects.

The presence of insulin-releasing natural product(s) in mistletoe may contribute to the reported antidiabetic property of the plant. The human implications of this study are unknown therefore the use of mistletoe with diabetes drugs should be administered with caution.

Elevations of liver enzymes have been reported with high doses of mistletoe. Seizure risk may be increased. Seizures have been reported to poison-control centers following the ingestion of crude mistletoe plant material. Immunomodulatory effects have also been proposed.

Theoretically, concomitant use of mistletoe and MAOIs may cause a hypertensive crisis due to mistletoe containing tyramine. Blood sugar levels may be altered by mistletoe. Mistletoe may have negative side effects on the eye and interact with eye drops.

Avoid use of mistletoe in hyperthyroid patients. The manufacturer of Iscador® warns that mistletoe may cause an inflammatory reaction when used during untreated hyperthyroidism.

According to secondary sources, concomitant use of mistletoe with antihypertensive agents may result in enhanced hypotensive effects of antihypertensive drugs.

One clinical trial reports that mistletoe adverse events include hypertension and hypotension. European mistletoe can have cardiotoxic and negative effects on heart beat strength, cause reflex bradycardia (slow heart rate), low blood pressure and depolarize cardiac muscle. Severe dehydration caused by mistletoe may lead to hypovolemic shock and cardiovascular collapse.

Use of mistletoe with CNS depressants may enhance sedative effects.

Alleged adverse side effects and complications tabulated include ascites, bradycardia, cardiac arrest, dehydration, hypotension, and negative inotropic effects. One clinical trial reports that mistletoe adverse events include hypertension and hypotension. European mistletoe can have cardiotoxic and negative inotropic effects, cause reflex bradycardia, hypotension and depolarize cardiac muscle. Severe dehydration caused by mistletoe may lead to hypovolemic shock and cardiovascular collapse.

Use of garlic or lime tree (Tilia platyphyllos) and mistletoe may result in additive blood pressure lowering action. Use of mistletoe with cholinergic herbs or supplements may cause increased myosis due to additive adverse effects. Use of hawthorne (Crataegus oxyacantha) and mistletoe may result in additive blood pressure lowering action.

Immunomodulatory effects have been proposed.

Elevations of liver enzymes have been reported with high doses of mistletoe.

Theoretically, concomitant use of mistletoe and MAOIs may cause a hypertensive crisis due to mistletoe containing tyramine.

The presence of insulin-releasing natural product(s) in mistletoe may contribute to the reported antidiabetic property of the plant. The human implications of this study are unknown therefore the use of mistletoe with diabetes drugs should be administered with caution.

Avoid use of mistletoe in hyperthyroid patients. The manufacturer of Iscador® noted mistletoe may cause an inflammatory reaction when used during untreated hyperthyroidism.

Theoretically, concomitant use of mistletoe and MAOIs may cause a hypertensive crisis due to mistletoe containing tyramine. Aged meats, cheese and wine also contain tyramine and may results in additive effects.