Is immediate release niacin helpful in controlling cholesterol ?

Yes: Niacin is a safe & effective way to lower LDL cholesterol while raising hdl. See http://www.Healthcentral.Com/cholesterol/c/7986/17940/myths-facts/2?Ic=2602 but also be aware that the role of cholesterol in heart disease is less than you may think! see http://www.Sott.Net/article/242516-heart-surgeon-speaks-out-on-what-really-causes-heart-disease & http://www.Spacedoc.Com/cholesterol_articles.

It Can Be: Immediate and extended release Niacin are the most effective formulations for lowering cholesterol. For comparable efficacy a higher doses of slow release Niacin preparations would be needed. Inositol and niacinamide not improve lipids and should be avoided.