Heterocyclic amines, also sometimes referred to as HCAs, are chemical compounds containing at least one heterocyclic ring, which by definition has atoms of at least two different elements, as well as at least one amine (nitrogen-containing) group. Typically it is a nitrogen atom of an amine group that also makes the ring heterocyclic (e.g., pyridine), though compounds exist in which this is not the case (e.g., the drug Zileuton). The biological functions of heterocyclic amines vary, including vitamins and carcinogens. Carcinogenic heterocyclic amines are created by high temperature cooking of meat and smoking of plant matter like tobacco. Some well known heterocyclic amines are niacin (vitamin B3), nicotine (psychoactive alkaloid and recreational drug), and the nucleobases that encode genetic information in DNA.