Is vasectomy considered a sin, given that the wife suffers from epilepsy and takes medications that could harm the fetus, and she cannot use other contraceptives?

The questioner's wife should have her fallopian tubes tied to prevent pregnancy due to the harm it poses to her and her fetus, and because she is unable to take contraceptive medications. However, he is not permitted to have his vas deferens tied, as harm is not repelled by harm, and celibacy and castration have been forbidden. As for reopening the tube, it is permissible if doctors determine that it would remove the harm without incurring similar or greater harm; otherwise, it is not permissible.