What side effects may I notice from receiving Niacin (Vitamin B3)?

Side effects that you should report to your doctor or health care professional as soon as possible:
-dark yellow or brown urine
-fainting spells
-grayish stool color
-nausea, vomiting
-palpitations
-severe stomach pain and loss of appetite
-shortness of breath, wheezing
-skin rash and itching
-weakness or tiredness
-yellowing of skin or eyes

Side effects that usually do not require medical attention (report to your doctor or health care professional if they continue or are bothersome):
-diarrhea
-headache
-stomach discomfort or bloating

This list may not describe all possible side effects for Niacin (Vitamin B3). Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.