The adverse effects of oral niacin/nicotinamide - an overview of reviews.

Nicotinamide(NAM) and niacin are forms of vitamin B3 commonly utilised as health supplements. Recent studies highlight its potential effects in glaucoma, leading to increasing use by patients. However, there are no studies on the adverse effects (AEs) of nicotinamide or niacin use in ophthalmology. We examined the incidence of clinically important AEs of oral NAM/niacin in humans and subsequent management strategies. A systematic search of reviews or meta-analyses was undertaken using pre-defined search criteria on PubMed with inclusion were agreed on by two independent researchers. Risk of bias assessment was performed using the ROBIS checklist.14 reviews were included, revealing the following: (1) Oral niacin and NAM were associated with a range of AEs including GI upset, liver dysfunction, flushing/vasodilatory effects, skin rash and fatigue. (2) Oral NAM is associated with a lower incidence of AEs than niacin. (3) AEs are more common with higher doses of oral NAM/niacin, and limits tolerability depending on co-morbid status (e.g.: renal dysfunction). (4) Only 6 reviews described discontinuation or reduction in dosage for AEs. (5) The majority of AEs diminished or resolved with reduction or discontinuation of oral niacin/NAM. AEs are diverse and dose-dependent, however, there remains a paucity of literature examining its side effects in a systematic manner. Standardised dosing, outcome measures and adverse effects should be utilised in further research and a surveillance system for reporting adverse effects. Regular clinical monitoring of AEs may not be indicated for doses of oral NAM under 1500 mg/day.