In the recommended oral amounts, mistletoe is rarely associated with side effects.¹⁸ Two reports, however, have confirmed the danger of ingesting mistletoe leaves and berries in large quantities, particularly when children accidentally eat the berries at Christmas.^{19, 20} Many of these exposures involved American mistletoe and not European mistletoe. European mistletoe is less toxic than the American species. If six to twenty berries or four to five leaves are eaten, then activated charcoal or ipecac can be used at home to induce vomiting. Emergency room care is only indicated if more than 20 berries or five leaves are ingested or if symptoms develop at lower levels of exposure. Possible symptoms of overdose are nausea, vomiting, low blood pressure, or dizziness.

Injectable forms of mistletoe may cause local redness and pain but otherwise have rarely been associated with serious side effects. There is one case report of a severe allergic reaction to an injected mistletoe preparation.²¹ Mistletoe is not recommended for use in children, or for women during pregnancy or breast-feeding.