Intravenous immunoglobulin (IVIG) contains immunoglobulin G (IgG), immunoglobulins that have been collected and concentrated from the plasma of thousands of blood donors. It currently cannot be synthesized in the laboratory. Infusion of IVIG is quite similar to blood transfusion and, as such, anaphylaxis and transfusion reactions can occur. The most common adverse effects include flushing, chills, headache, muscle aches, wheezing, lower back pain, low blood pressure, and increased heart rate. While IVIG is FDA approved for several conditions in adults, it is frequently used "off label" for many indications, many of which are neurological conditions, such as Guillain-Barré syndrome in myasthenia gravis.