Should I take niacin or niacinamide if 50 mg of niacin in my multi-vitamin caused me to flush within 1 to 2 hours of taking it?

Low doses of niacin (25 mg twice a day after meals) should not cause flushing, is sufficient, and is easily metabolized.  However, if you are hypersensitive, you can take ½ (81 mg) of a pediatric aspirin just before each niacin dose to prevent flushing or else do use niacinamide.  The mechanism of niacin flush is quite different from, and unrelated to, that of carcinoid syndrome.