The Church believes and confesses that among the seven sacraments there is one especially intended to strengthen those who are being tried by illness, the Anointing of the Sick:
This sacred anointing of the sick was instituted by Christ our Lord as a true and proper sacrament of the New Testament. It is alluded to indeed by Mark, but is recommended to the faithful and promulgated by James the apostle and brother of the Lord. (Council Of Trent (1551): DS 1695; cf. Mk 6:13; James 5:14-15.)
In this sacrament, it is Jesus who touches the sick to heal them from sin – and sometimes even from physical ailment. His cures were signs of the arrival of the Kingdom of God. The core message of his healing tells us of his plan to conquer sin and death by his dying and rising.
The Anointing of the Sick is given to those who are seriously ill by anointing them on the forehead and hands with duly blessed oil - pressed from olives or from other plants - saying, only once:
Through this holy anointing may the Lord in his love and mercy help you with the grace of the Holy Spirit. May the Lord who frees you from sin save you and raise you up. (Code of Canon Law, 847 § 1)
When the Sacrament of Anointing of the Sick is given, the hoped-for effect is that, if it be God's will, the person be physically healed of illness. But even if there is no physical healing, the primary effect of the Sacrament is a spiritual healing by which the sick person receives the Holy Spirit's gift of peace and courage to deal with the difficulties that accompany serious illness or the frailty of old age.
WHO RECEIVES AND WHO ADMINISTERS THIS SACRAMENT?
The Anointing of the Sick "is not a sacrament for those only who are at the point of death. Hence, as soon as anyone of the faithful begins to be in danger of death from sickness or old age, the fitting time for him to receive this sacrament has certainly already arrived." (Sacrosanctum Concilium 73; Code of Canon Law, 1004 § 1; 1005; 1007)
The Rite of Anointing tells us there is no need to wait until a person is at the point of death to receive the Sacrament. A careful judgment about the serious nature of the illness is sufficient.
If a sick person who received this anointing recovers his health, he can in the case of another grave illness receive this sacrament again. If during the same illness the person's condition becomes more serious, the sacrament may be repeated. It is fitting to receive the Anointing of the Sick just prior to a serious operation. The same holds for the elderly whose frailty becomes more pronounced.
Is there any sick among you? Let him send for the presbyters of the Church, and let them pray over him, anointing him with oil in the name of the Lord. And the prayer of faith shall save the sick person, and the Lord shall raise him up; and if he has committed any sins, they shall be forgiven him. - James 5:14-15
Only priests (bishops and presbyters) are ministers of the Anointing of the Sick. (Council Of Trent (1551): DS 1697; 1719; Code of Canon Law 1003). It is the duty of pastors to instruct the faithful on the benefits of this sacrament. The faithful should encourage the sick to call for a priest to receive this sacrament. The sick should prepare themselves to receive it with good dispositions, assisted by their pastor and the whole ecclesial community, which is invited to surround the sick in a special way through their prayers and fraternal attention.
(From The Catechism of the Catholic Church, 1511-1516)