What side effects may I notice from receiving Diphenhydramine?

Side effects that you should report to your doctor or health care professional as soon as possible:

-allergic reactions like skin rash, itching or hives, swelling of the face, lips, or tongue
-changes in vision
-confused, agitated, or nervous
-fast, irregular heartbeat
-tremor
-trouble passing urine or change in the amount of urine
-unusual bleeding or bruising
-unusually weak or tired
Side effects that usually do not require medical attention (report to your doctor or health care professional if they continue or are bothersome):

-constipation, diarrhea
-drowsy
-headache
-loss of appetite
-stomach upset, vomiting
-thick mucus

This list may not describe all possible side effects for Diphenhydramine. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.