What’s the Danger with Decongestants and Antihistamines?

Why do over-the-counter decongestants or antihistamines warn that they are not to be used by people with diabetes?

Robert Williams
Fort Worth, Texas

They can be used by people with diabetes, but with caution.


Decongestants are similar to adrenaline, thus they can cause blood vessels to constrict and increase blood pressure. Also, as with adrenaline, decongestants can release sugar into the blood stream and raise blood sugars. For most people, it is not a big deal. To see if it is a big deal for you, test your blood sugar, take the decongestant, then keep testing to see what happens.

The problem lies in the fact that if you require a decongestant, you are probably already sick, so your blood sugars are high anyway. Caution is advised.


Antihistamines have a slight decongestive effect, but not enough to worry about. One danger is that antihistamines can make you drowsy, and you may forget to test your blood sugars.

R. Keith Campbell, RPh, CDE
Professor of Pharmacy
Washington State University
Pullman, Washington

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