The National Catholic Bioethics Center has a discussion as well as publications concerning end of life issues. There is a brief discussion of euthanasia
here. It is always wrong to directly intend to kill a patient, but it is not wrong to give sufficient dosage of pain medication to control suffering, even if time of death is thereby advanced.
“Although it is certainly preferable to die in a conscious state of prayer, no one should feel obliged to forgo medications and pain relief even though they may bring about disorientation or produce unconsciousness. The Church does not oblige the Catholic to forgo medical treatment for pain even when such treatment may deprive the patient of full consciousness or indirectly shorten life. This is an application of the principle of double-effect (see glossary). The Church asks only that appropriate conditions exist before such medication be taken.”
Source:
ncbcenter.org/eol.asp