Nicotinamide dinucleotide phosphate (NADPH) plays important roles in redox metabolism, reductive biosynthesis, and signal transduction. There are several studies reported that NADPH has neuroprotective effects in animal models of ischemic stroke. However, the molecular mechanisms underlying its neuroprotection remain largely unknown. In this chapter, we will summarize the recent studies on the effects of nicotinamide co-enzymes on platelet functions. The findings of suppressing platelet aggregation by NADPH could attribute in part to its pharmacological effects in animal models of ischemic stroke.