Chemical castration will have most of the same effects as castration and is sometimes used to dull the sexual drives of sex offenders. It involves taking certain hormones and drugs that simulate the effects of castration by altering the body's chemical and hormonal balance. In general this means anti-androgens which block testosterone or testosterone production.
Chemical castration is also a preliminary step in hormone treatment by male to female transsexuals, and used as a "test drive" for those who wish to try out castration before acutally having themselves castrated.
There are a number of different drugs and hormones used for this purpose, including Androcur and Depo-Provera.