Niacin is heavily promoted on the internet for depression.  For instance, www.wholehealthmd.com says that niacin "may fight depression....some experts recommend the vitamin for relieving depression as well as for soothing feelings of anxiety and panic" (8/5/05).  Who these "experts" are is unknown.  I have been unable to find a single scientific study of the use of niacin for depression.  The only scientific references for mental illness I have found are very old and state that studies have not found any benefit for niacin in the treatment of psychiatric disease.

www.nowfoods.com makes a definitely bogus claim in its attempt to sell niacin to the unsuspecting public: "Niacin is widely regarded as one of the most effective nutrients in elevating mood, overcoming moderate depression and fighting the effects of fatigue" (NOW catalog, Summer, 2005).  This is clearly not true.  While 5-HTP, thiamine, fish oil, SAMe, and folate all have limited but favorable research for treating depression as documented on this website, niacin has none. 

The Orthomolecular megavitamin crowd, led by Abram Hoffer having been promoting niacin and pyridoxine (B-6) for decades as a cure-all, but there are no studies on PubMed using it for depression, nor have I been able to find any references to studies for depression on the internet.

See Niacin for Heart Disease for more favorable information for that indication.

No Evidence for Niacin for Mental Disorders: Of 53 controlled trials of the effects of niacin, vitamin B6, and multivitamins on mental functions reviewed, virtually all trials show serious short-comings: in the number of participants, the presentation of baseline characteristics and outcomes, and the description of changes in concomitant treatments. Only in autistic children are some positive results are found with very high dosages of vitamin B6 combined with magnesium, but further evidence is needed before more definitive conclusions can be drawn. Niacin and vitamin B6 in mental functioning: a review of controlled trials in humans. Kleijnen et al. University of Limburg, The Netherlands. Biol Psychiatry. 1991 May 1;29(9):931-41.

Niacin and B-6 Useless for Schizophrenia: As part of the Canadian Mental Health Association Collaborative Study, in a 48-week study in which supplementation of neuroleptic treatment with a single vitamin, i.e., nicotinic acid or pyridoxine, was done for schizophrenic patients in a DB PC design, no benefit from the vitamins was found. The use of nicotinic acid and pyridoxine in the treatment of schizophrenia. Petrie WM, et al. Int Pharmacopsychiatry. 1981;16(4):245-50; Arch Gen Psychiatry. 1973 Mar;28(3):308-15; Lancet. 1962 Feb 10;1:316-9.