Vitamin B complex. A tablet of vitamin B complex, a group of vitamins that consists of thiamine (vitamin B1), riboflavin (vitamin B2), niacin, pantothenic acid, pyridoxine (vitamin B6), biotin (vitamin H), and folic acid. These water-soluble vitamins are necessary for many enzyme reactions in the body. They are important for the proper functioning of the nervous system, heart, muscles, digestive system, skin, and for growth and development. This group of vitamins can also be obtained from vegetables, fruit, whole grains, wheat-germ, egg yolk, fish and liver.