Are there any possible side effects?

No, the supplement is derived from whole foods.

Niacin

Niacin causes the blood vessels to dilate, resulting in a flushed appearance. Some people may even experience itching or a rash associated with taking niacin. Most people who experience reactions to niacin do so after taking doses of 75mg or higher. Some may experience reactions with doses as low as 50mg, and for others it may take higher than 75mg to produce a reaction. The reactions are all considered normal and harmless, most reactions only last 20 minutes or less. Every person’s chemistry is different. As in any case, consult your Healthcare or Medical practitioner before taking any medication or supplement.

Ref: http://www.doctoryourself.com/niacin.html