Allergy shots – also known as immunotherapy – can have side effects, like all medical treatments. Allergy shots should not be considered without at least an attempt at avoidance of the allergen, but there are cases where it is nearly impossible to avoid an allergen. A person with cat allergies could much more easily avoid their allergen than someone with a grass pollen allergy, for example.
When a patient receives allergy shots, they are exposed to closely regulated allergens on a scheduled basis. Over a period of time, trace amounts of the allergens are given to constitute maintenance doses. These maintenance doses encourage the body to produce blocking antibodies – also known as IgG antibodies – and decrease the amount of allergic (IgE-mediated) antibodies.