Nature's Bounty Dual Spectrum B-12 Dietary Supplement is an innovative way to support energy by converting food into energy. Each bi-layer B-12 tablet features ISR Technology, a scientifically engineered delivery mechanism that offers the benefits of both immediate and sustained release (ISR). Each tablet has two distinct layers--one to deliver effective, quick release, and one designed to release B-12 in your body over the course of several hours--when you need it most.