Can my friend be chemically castrated?
In Scripture, Jesus tells us that if a hand is causing us to sin, we should cut it off, and if an eye is causing us to sin, we should gouge it out. A married friend of mine is stumbling due to sexual sin and has asked whether it would be okay for him to get chemically castrated. (He has been told that being chemically castrated would end his sex drive). If the answer is "No, it would not be okay" then how does that jive with Christ's words in the Gospels?
No, it would not be okay for your friend to chemically castrate himself. Chemical castration would be a form of sterilization and the Church forbids direct sterilization. Jesus did not intend to be taken literally; he was using a literary device called hyperbole (i.e., a figure of speech used to emphasize the importance of what is being said). It may interest your friend to know that the early Christian writer Origen is said to have made the same mistake he has, which is to say that Origen also took Jesus' words literally and castrated himself -- although he did not do so chemically -- to prevent himself from falling into sexual sin.
A second problem with your friend's plan of action is that it would mean that he would deprive his wife of her right to marital relations with him, something he promised to her in marriage. Even if his wife agreed to the chemical castration, however, he could not licitly have it done.
The answer to your friend's problem is the same as the answer would have been for Origen. Those who stumble into sexual sin are called to self-mastery, not self-mutilation. By means of frequent recourse to the sacraments, especially confession, your friend can learn self-control and master his problem. Achieving self-mastery is the more difficult route, but ultimately much more satisfying than rendering himself incapable of sexual sin.