Page "H1 antagonist" Paragraph 4

While H < sub > 1 </ sub >- antihistamines help against these effects, they work only if taken before contact with the allergen.

In severe allergies, such as anaphylaxis or angioedema, these effects may be so severe as to be life-threatening.

Additional administration of epinephrine, often in the form of an autoinjector ( Epi-pen ), is required by people with such hypersensitivities.