Vitamin B15 is an older, now largely abandoned name for substances sold as pangamic acid — sometimes identified with orotic acid — once marketed as a vitamin-like supplement. It was promoted in mid-twentieth-century alternative medicine for athletic performance, heart conditions, and ageing, but it was never recognised as an essential nutrient: no deficiency disease exists, and mainstream nutrition science does not classify it as a vitamin. Regulatory authorities in several countries have acted against its sale with therapeutic claims. The B15 story is a cautionary tale about vitamin nomenclature — numbers once assigned casually stuck in supplement marketing long after science moved on — and about the gap between marketing and evidence.