When someone has a life-threatening reaction that is allergy-related, they are usually given an auto-injectable pen of epinephrine. The question, what does this pen do?
First, we need to understand what is happening in a life-threatening reaction. 2 types of immune cells called basophils and Mast cells, have become activated to a substance the body has deemed a threat, and thus created antibodies to. These cells release a heavy amount of inflammation-causing cytokines to kill this perceived intruder. These cytokines include leukotrienes and histamine. They cause large system wide-body effects including hives, vomiting, wheezing, swelling, low blood pressure, and rarely: death. This system-wide reaction is called anaphylaxis.
Epinephrine is a hormone our body produces, which gives us bursts of energy. It also has the effect of stopping mast cells and basophils from releasing their contents. Epinephrine has system-wide effects including opening the lungs, increasing blood pressure, decreasing swelling, and thus reversing anaphylaxis. And thus its a life-saving injection in times of acute severe allergic reactions.
There is no contraindication to epinephrine and should be used at first signs of life-threatening reactions due to an allergy.