The Talmud discusses the "Kos Shel Ikrin" (Cup of the Barren, or Cup of Roots), a potion that rendered a woman or man infertile. The recipe for this potion is on record in tractate Shabbos and there was no question that this potion did exactly what it was purported to do (see Yevamos 65b, Shabbos 110b, and many other sources). In fact, its success was certain (see Tosafos in Shabbos 110b). Apparently the brewing of a Kos Shel Ikrin was still a known process in the days of the Rambam (he describes the ingredients in his Perush LeMishnayos).
Does such a potion exist today?