Why the Thigh?

Most people that carry epinephrine to treat serious allergic reactions will tell you they were given strict instructions to inject the needle into their outer thigh. They may also tell you that the needle can be injected over clothing, if necessary.

For years I carried epinephrine because I received weekly seasonal allergy injections. Today I carry epinephrine for my food-allergic child. For a long time, I didn’t know why I was advised to inject the needle into my thigh. My hunch is that most people don’t know why either.

Several years ago, the Journal of Allergy and Clinical Immunology published a study measuring epinephrine absorption in children with a history of anaphylaxis. The participants were randomly assigned to receive a single injection of epinephrine either subcutaneously (under the skin) or intramuscularly (in muscle).

Among children that received epinephrine subcutaneously, epinephrine absorption was considerably slower than for those that received the injection intramuscularly. 

A few years later, the same clinical journal published this study. Their goal was to measure epinephrine absorption in adults intramuscularly versus subcutaneously, but also evaluate absorption differences between two different intramuscular sites: the thigh and the upper arm.

The results of this latter study (below) support the recommendation that epinephrine should be administered in the outer thigh. Greater blood flow in the thigh was considered the likely reason why the absorption rate was higher relative to the upper arm. 

Failure to timely administer epinephrine during an allergic reaction is the leading cause of fatalities among the food allergic, which is why it’s so important to carry epinephrine if you have a food allergy. These findings further underscore the importance of administering the needle into the thigh, as delayed epinephrine absorption could have serious implications during life-threatening episodes of anaphylaxis.

So now you know, folks! Raise your epinephrine high to the sky, then swing it firmly into the thigh!

— Meg and the Allergy Amulet Team