Salt peter really doesn't work, except it will make you sick which will probably reduce libido.
http://www.snopes.com/military/saltpetr.htm
You might want to check with a doctor about ways to reduce it rather then home remedies. You might want to talk to a psychiatrist about why you want to reduce your libido..just something screwey like that.
Of course the suggestion of birth control works wonders if you are a girl. I spend $25 a month so I don't have sex with my fiance. Like someone said earlier in the thread, the stuff may not even work because I never get a chance to try it out.
Sorry for thread jacking like everyone else