Vitamin B12 or cobalamin is an essential nutrient that plays a vital role in human health. Because it is considered that active forms of B12 cannot be reliably obtained from plant foods or algae, the position of the Academy of Nutrition and Dietetics is that:
Vegans need reliable sources of vitamin B-12, such as fortified foods or supplements.
Now, the vitamin itself is of vegan origin. It is produced by a wide range of bacteria that reside in the soil and in the guts of some animals, and supplements are obtained by cultivating those microorganisms. According to Wikipedia:
My concern lies in knowing whether the growth medium used in the cultivation of these bacteria is vegan. Some types of microorganism growth media, such as blood agar and chocolate agar, use blood as an ingredient. Others might use lactose or beef extract.
Of course, taking B12 supplements would still meet the Vegan Society’s definition of ‘vegan’ since, as we’ve already established, B12 is vital to humans and the only way to obtain it is through direct or indirect supplementation.
Veganism is a way of living which seeks to exclude, as far as is possible and practicable, all forms of exploitation of, and cruelty to, animals for food, clothing or any other purpose.
The Vegan Society DOES NOT recommend you avoid medication prescribed to you by your doctor - a dead vegan is no good to anyone!