From the Catechism of the Catholic Church
Catholic teaching labels euthanasia as 'murder' while making a clear distinction between euthanasia and refusing 'overzealous' or 'extraordinary' medical treatment.
2277 Whatever its motives and means, direct euthanasia consists in putting an end to the lives of handicapped, sick or dying persons. It is morally unacceptable.
Thus an act or omission which, of itself or by intention, causes death in order to eliminate suffering constitutes a murder gravely contrary to the dignity of the human person and to the respect due to the living god, his Creator. The error of judgement into which one can fall in good faith does not change the nature of this murderous act, which must always be forbidden and excluded.
2278 Discontinuing medical procedures that are burdensome, dangerous, extraordinary, or disproportionate to the expected outcome can be legitimate.
2279 Even if death is thought imminent, the ordinary care owed to a sick person cannot be legitimately interrupted. The use of painkillers to alleviate the sufferings of the dying, even at the risk of shortening their days, can be morally in conformity with human dignity if death is not willed as either an end or a means, but only foreseen and tolerated as inevitable. Palliative care is a special form of disinterested charity. As such it should be encouraged.
Other relevant quotes
Those who are ill must never be made to feel they are a burden.
"Sickness is a call to Christians to demonstrate true compassion. Likewise, the handicapped and those who are ill must never feel that they are a burden: they are persons being visited by the Lord. The terminally ill in particular deserve the solidarity, communion and affection of those around them."
(Pope John Paul II. (1998). Ad Limina Address to Bishops of California, Nevada and Hawaii, USA).
People's request for euthanasia a plea for help rather than a desire to die.
"It may happen that, by reason of prolonged and barely tolerable pain, for deeply personal or other reasons, people may be led to believe that they can legitimately ask for death or obtain it for others. Although in these cases the guilt of the individual may be reduced or completely absent, nevertheless the error of judgement into which the conscience falls does not change the nature of this act of killing, which will always be in itself something to be rejected. The pleas of gravely ill people who sometimes ask for death are not to be understood as implying a true desire for euthanasia; in fact, it is almost always a case of an anguished plea for help and love. What a sick person needs, besides medical care, is love, to be surrounded by all those close to him or her, parents and children, doctors and nurses."
(Sacred Congregation for the Doctrine of the Faith. (1980). Declaration on Euthanasia)
On the nature of the physician-patient relationship.
"To destroy the boundary between healing and killing would mark a radical departure from longstanding legal and medical traditions of our country, posing a threat of unforeseeable magnitude to vulnerable members of our society. Those who represent the interests of elderly citizens, persons with disabilities, and persons with AIDS or other terminal illnesses, are justifiably alarmed when some hasten to confer on them the "freedom" to be killed."
(Administrative Committee, National Conference of US Catholic Bishops. (1991). Statement on Euthanasia.)
There is a direct correlation between the way society views the elderly and attitudes to euthanasia. the "normal requirements of medical care" are what is obligatory.
"In the past, great respect was shown to the elderly. If we stop to see the current situation, we see that among peoples old age is [still] esteemed and valued while among others, this is much less the case, due to a mentality which gives priority to immediate human usefulness and productivity. Such an attitude frequently leads to contempt for the later years of life, while older people themselves are led to wonder whether their lives are still worthwhile.It has come to the point where euthanasia is increasingly put forward as a solution for difficult situations. Certainly it can happen that, when grave illness involves unbearable suffering, the sick are tempted to despair and their loved ones or those responsible for their care feel compelled by a misguided compassion to consider the solution of 'an easy death' as something reasonable. Here it should be kept in mind that the moral law allows the rejection of 'aggressive medical treatment' and makes obligatory only those forms of treatment which fall within the normal requirements of medical care, which in the case of terminal illness seeks primarily to alleviate pain. But euthanasia, understood as directly causing death, is another thing entirely. Regardless of intentions and circumstances, euthanasia is always an intrinsically evil act, a violation of god's law and an offense against the dignity of the human person."
(Pope John Paul II. (1999). Letter to the Elderly)
Euthanasia as an expression of discrimination rather than freedom.
"Remarkably, few have noticed that frail, elderly and terminally ill people oppose assisted suicide more than other Americans. The assisted-suicide agenda is moving forward chiefly with vocal support from the young, the able-bodied and the affluent. Thus the assisted suicide agenda appears as a victory not for freedom, but for discrimination. At its heart lie demeaning attitudes and prejudices about the value of life with an illness or disability. All who believe in the dignity of human beings should reject such attitudes.
Catholic physicians, nurses, chaplains and others are on the front lines in providing compassionate care for suffering patients. They know, as we do, that the humane approach to dying patients is to eliminate their physical suffering and other problems, not to eliminate the patient. They know, as Pope John Paul II has said, that 'true compassion leads to sharing another's pain; it does not kill the person whose suffering we cannot bear'.
(National Conference of US Catholic Bishops. (1996). Choosing the Path to Life)
Death; a decisive phase of life requiring attention to every aspect of our existence.
In the face of the mystery of death people are helpless; human certitudes begin to wave. However, it is precisely in the face of this setback that Christian faith, if it is understood and accepted in all its richness, offers itself as a source of serenity and peace. What seemed to be meaningless acquires sense and value. When there is no reference to the saving message of faith and hope, the consequence is that the appeal of charity is weakened, and utilitarian and pragmatic principles enter into play which ultimately hold that it is logical and even justifiable to take a life that has been a burden to self or others.
Life is a gift from the Creator. It is to be accepted, respected and promoted with every means available, and defended from every threat. Death is truly a mysterious moment, an event during which the person should be treated with affection and respect. Most of all, a person who is hanging between life and death needs a loving presence. the awareness that the dying person will soon meet God for all eternity should impel his or her relatives, loved ones, the medical, health-care and religious personnel, to help him or her in this decisive phase of life, with concern that pays attention to every aspect of existence, including the spiritual. Those who are sick, and the dying most of all must not lack the affection of their relatives, the care of medical personnel, or the support of their friends. Experience teaches that the help given the dying person from faith in God and hope in eternal life is of fundamental importance, even more so than human comforts.
(Pope John Paul II. (1992). Faith responds to fears about death: The Holy Father's address to an international congress on the care of the dying.)
On the relationship between civil law and moral sensitivity, and the influence of law on the formation of conscience.
A source of particular concern, however, is the fact that people's moral conscience appears frighteningly confused and they find it increasingly difficult to perceive the clear and definite distinction between good and evil in matters concerning the fundamental value of human life.
However serious and disturbing the phenomenon of the widespread destruction of so many human lives, either in the womb or in old age, no less serious and disturbing is the blunting of the moral sensitivity of people's consciences. Laws and civil ordinances not only reflect this confusion but they also contribute to it. When legislative bodies enact laws that authorise putting innocent people to death and states allow their resources and structures to be used for these crimes, individual consciences, often poorly formed, are all the more easily led into error. In order to break this vicious circle, it seems more urgent than ever that we should forcefully reaffirm our common teaching, based on sacred Scripture and tradition, with regard to the inviolability of innocent human life.
(Pope John Paul II. (1991). Excerpt from a letter to each Bishop throughout the world concerning the inviolability of the right to life.)
Euthanasia Glossary of Terms
Euthanasia Hospice New Zealand Position Statement