Drug interaction of humira (adalimumab) with niacin can taking niacin affect the effectiveness of humira (adalimumab)?

No. Though interactions were reported in patients taking these two agents, Humira (adalimumab) and niacin, the patients were taking multiple other medications. It was not shown to be an interaction between the Niacin and humira (adalimumab). To test it individually, the Niacin could simply be stopped for a month assuming the Niacin was being used to treat hyperlipidemia. Ask your doctor if it is safe to hold the niacin.