3 doctors weighed in:
What is the average time needed for an antihistamine to begin to work?
3 doctors weighed in

Dr. Steven Machtinger
Internal Medicine - Allergy & Immunology
1 doctor agrees
In brief: 45-90 minutes
Antihistamines taken by mouth begin to work in about an hour but may take longer if you've just eaten.
Antihistamine nasal sprays (astepro, patanase) begin to work in 30 minutes. An antihistamine injection, usually diphenhydramine, sometimes given for a severe allergic reaction or anaphylaxis begins to work in a few minutes.

In brief: 45-90 minutes
Antihistamines taken by mouth begin to work in about an hour but may take longer if you've just eaten.
Antihistamine nasal sprays (astepro, patanase) begin to work in 30 minutes. An antihistamine injection, usually diphenhydramine, sometimes given for a severe allergic reaction or anaphylaxis begins to work in a few minutes.
Dr. Steven Machtinger
Dr. Steven Machtinger
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Dr. Lee Perry
Internal Medicine - Allergy & Immunology
In brief: Depends
It depends on the antihistamine, but most begin working within 3-4 hours of administration.

In brief: Depends
It depends on the antihistamine, but most begin working within 3-4 hours of administration.
Dr. Lee Perry
Dr. Lee Perry
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