Niacin was used in the 1930-50s to "cure" Depression and other mental problems. It has been used by the AA help with depression. It has been involved in many double-blind studies that show it works. Most people don't like it because of the flush. There are many other nutrtional suppliments that may be in play. It is important to provide your body with a constant source of whole food vitamins and minerals.
Don't take timed release niacin. It can cause problems for some people.
Don't take megadose (over 1500 to 2000mg) for more then a week.
Check if you are taking any meds for contradictions.