To evaluate the effect of niacinamide, on selected parameters of osteoarthritis using a double-blind, placebo controlled study design.Seventy two patients with osteoarthritis were randomized for treatment with niacinamide or an identical placebo for 12 weeks. Outcome measures included global arthritis impact and pain, joint range of motion and flexibility, erythrocyte sedimentation rate, complete blood count, liver function tests, cholesterol, uric acid, and fasting blood sugar. Compliance was monitored with a pill record sheet and interview.Global arthritis impact improved by 29% (95% confidence interval [CI] 6, 46) in subjects on niacinamide and worsened by 10% in placebo subjects (p = 0.04). Pain levels did not change but those on niacinamide reduced their anti-inflammatory medications by 13% (95% CI 9, 94; p = 0.01). Niacinamide reduced erythrocyte sedimentation rate by 22% (95% CI 6, 51; p < 0.005) and increased joint mobility by 4.5 degrees over controls (8 degrees vs 3.5 degrees; p = 0.04). Side effects were mild but higher in the niacinamide group (40% vs 27%, p = 0.003).This study indicates that niacinamide may have a role in the treatment of osteoarthritis. Niacinamide improved the global impact of osteoarthritis, improved joint flexibility, reduced inflammation, and allowed for reduction in standard anti-inflammatory medications when compared to placebo. More extensive evaluation of niacinamide in arthritis is warranted.