Safety of mistletoe therapy

Mistletoe therapy is characterised by good tolerability [23, 24, 25, 28]. According to a Cochrane analysis, the adverse events associated with mistletoe extracts were generally mild; no serious or life-threatening events were observed [6]. 

Frequent adverse, dose-dependent and spontaneously resolving events include inflammatory reactions at the injection site, elevated temperature or slight fever, and flu-like symptoms.  

According to the summary of product characteristics provided by mistletoe manufacturers, "a slight increase in body temperature and local inflammatory reactions at the subcutaneous injection site at the beginning of therapy are almost regular". They are regarded as "signs of the patient's state of reaction" and thus are considered as a positive immune reaction. Temporary slight swelling of regional lymph nodes is also harmless. According to the Onkopedia guidelines on complementary and alternative therapies [26] these symptoms are typical for the stimulation of the body's own defence system. In terms of the anthroposophic therapeutic concept, these reactions are desired and serve as a criterion for individual dose adjustment.

The local reactions at the injection site in terms of redness, which may also be accompanied by induration, swelling, itching, hyperthermia or pain, usually only become apparent at the beginning of treatment. Very rarely (0.1-1%) allergic or pseudoallergic reactions have been observed [29, 30, 31, 32, 33, 34, 35, 36, 37, 38]. The presence of anti-ML-1 antibodies of the IgE type may play a role in type 1 allergic reactions [37]. 

According to the manufacturers, mistletoe extracts should be avoided in cases of known allergies to mistletoe preparations , in chronic granulomatous diseases, florid autoimmune diseases, and in immunosuppressive therapy [1, 2, 3, 4]. In the case of acute inflammatory or highly febrile diseases, application should be paused until the signs of inflammation have subsided. 

Special caution should be taken when simultaneously treating with other immunomodulating drugs (e.g. interferons, interleukins), due to the risk of overstimulation [1, 2, 3, 4].

According to Onkopedia guidelines, mistletoe therapy is not recommended for cancers which originate from the immune system (e.g. leukaemias, lymphomas) [26]; these indications are also considered as off-label use.