3 doctors weighed in:

Why does drowsiness occur after taking antihistamines?

3 doctors weighed in
Dr. Patrick Melder
ENT - Head & Neck Surgery
1 doctor agrees

In brief: Complex

Histamine is a wake promoting neurotransmitter in the brain.
Older antihistamines like Benadryl (diphenhydramine) cross into the brain and block this center allowing for drowsiness to occur. The newer antihistamines like alleges, claritin, zyrtec do not cross as easily and are less likely to promote drowsiness.

In brief: Complex

Histamine is a wake promoting neurotransmitter in the brain.
Older antihistamines like Benadryl (diphenhydramine) cross into the brain and block this center allowing for drowsiness to occur. The newer antihistamines like alleges, claritin, zyrtec do not cross as easily and are less likely to promote drowsiness.
Dr. Patrick Melder
Dr. Patrick Melder
Thank
Dr. Jack Mutnick
Internal Medicine - Allergy & Immunology

In brief: Blood Brain Barrier

Any antihistamine that crosses the blood brain barrier can cause sedation and drowsiness.
There are at least four types of histamine receptors in the body and they can be acted on as well. There are also 1st generation and 2nd generation antihistamines which have varying drowsy classifications.

In brief: Blood Brain Barrier

Any antihistamine that crosses the blood brain barrier can cause sedation and drowsiness.
There are at least four types of histamine receptors in the body and they can be acted on as well. There are also 1st generation and 2nd generation antihistamines which have varying drowsy classifications.
Dr. Jack Mutnick
Dr. Jack Mutnick
Thank
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