Nature's Plus Mega B-150 Sustained Release - 90 Tablets Nature's Plus is pleased to offer the highest potency B-Complex available in an all-natural rice bran base. Mega B-150 contains no yeast and is easily digested and absorbed. B-ComplexThe vitamin B-complex refers to all of the known essential water-soluble vitamins except for vitamin C. These include thiamine (vitamin B1), riboflavin (vitamin B2), niacin (vitamin B3), pantothenic acid (vitamin B5), pyridoxine (vitamin B6), biotin, folic acid and the cobalamins (vitamin B12). "Vitamin B" was once thought to be a single nutrient that existed in extracts of rice, liver, or yeast. Researchers later discovered these extracts contained several vitamins, which were given distinguishing numbers.