Bluebonnet s Flush-Free Niacin 500 mg vitamin capsules provide pure crystalline inositol hexanicotinate (known as flush-free niacin) in easy-to-swallow vegetable capsules for maximum assimilation and absorption. Niacin is used for treating high cholesterol. It can also be used along with other treatments for circulation problems migraine headaches dizziness and to reduce diarrhea associated with cholera.