When you get an allergy shot, a small amount of allergen is injected under the skin, usually in the fleshy part of the upper arm. In the beginning, injections are typically given once a week. After that, the doses of allergen are increased gradually with each injection.
The maximum dose, called a maintenance dose, is reached after four to six months. The maintenance dose is given once a week or once every two weeks. After several months, the injection schedule may be reduced to once every three or four weeks. A full course of allergy shots usually takes between three and five years.