• Crystalline niacin is used to treat high cholesterol."OatFlan" is Copyrighted by Flickr user: Mornflake (Mornflake Oats) under the Creative Commons Attribution license.
  
  

Uses

• Crystalline niacin often is used to treat high cholesterol and niacin deficiency, according to MayoClinic.com. It also has been used to prevent hardening of the arteries and to prevent second heart attacks.
  
  

Dose

• Taking niacin with food can reduce stomach upset. Doses have ranged from 375 milligrams to 3 grams in clinical studies, according to the Mayo Clinic.
  
  

Allergy

• Rare cases of anaphylactic shock as result of an allergy have been reported after taking crystalline niacin. Tell your doctor about any allergies you have before taking niacin.
  
  

Mild Side Effects

• Skin flushing accompanied by a warm sensation is common while taking crystalline niacin. Itching and dry skin are often common when taking vitamin B3, as well.
  
  

Severe Side Effects

• Aggravation of stomach ulcers and liver toxicity are possible side effects of crystalline niacin. Your doctor will monitor your blood for signs of these issues while you take niacin.