Cecil replies: The official word is that potassium nitrate (KNO3), more commonly employed as an ingredient in gunpowder, has no therapeutic value as an anaphrodisiac, contrary to legend. Cecil of course believes this. Still, when you look at what the stuff does do, you can see where the idea got started. Saltpeter can cause relaxation of involuntary muscle fiber (for which reason it's used to treat asthma) and it's occasionally prescribed to lower body temperature in cases of fever.