Objection 1. It seems that the priest who consecrates is not bound to receive this sacrament. Because, in the other consecrations, he who consecrates the matter does not use it, just as the bishop consecrating the chrism is not anointed therewith. But this sacrament consists in the consecration of the matter. Therefore, the priest performing this sacrament need not use the same, but may lawfully refrain from receiving it.
Objection 2. Further, in the other sacraments the minister does not give the sacrament to himself: for no one can baptize himself, as stated above (66, 5, ad 4). But as Baptism is dispensed in due order, so also is this sacrament. Therefore the priest who consecrates this sacrament ought not to receive it at his own hands.
Objection 3. Further, it sometimes happens that Christ's body appears upon the altar under the guise of flesh, and the blood under the guise of blood; which are unsuited for food and drink: hence, as was said above (Question 75, Article 5), it is on that account that they are given under another species, lest they beget revulsion in the communicants. Therefore the priest who consecrates is not always bound to receive this sacrament.
On the contrary, We read in the acts of the (Twelfth) Council of Toledo (Can. v), and again (De Consecr., dist. 2): "It must be strictly observed that as often as the priest sacrifices the body and blood of our Lord Jesus Christ upon the altar, he must himself be a partaker of Christ's body and blood."
I answer that, As stated above (79, 5,7), the Eucharist is not only a sacrament, but also a sacrifice. Now whoever offers sacrifice must be a sharer in the sacrifice, because the outward sacrifice he offers is a sign of the inner sacrifice whereby he offers himself to God, as Augustine says (De Civ. Dei x). Hence by partaking of the sacrifice he shows that the inner one is likewise his. In the same way also, by dispensing the sacrifice to the people he shows that he is the dispenser of Divine gifts, of which he ought himself to be the first to partake, as Dionysius says (Eccl. Hier. iii). Consequently, he ought to receive before dispensing it to the people. Accordingly we read in the chapter mentioned above (Twelfth Council of Toledo, Can. v): "What kind of sacrifice is that wherein not even the sacrificer is known to have a share?" But it is by partaking of the sacrifice that he has a share in it, as the Apostle says (1 Corinthians 10:18): "Are not they that eat of the sacrifices, partakers of the altar?" Therefore it is necessary for the priest, as often as he consecrates, to receive this sacrament in its integrity.
Reply to Objection 1. The consecration of chrism or of anything else is not a sacrifice, as the consecration of the Eucharist is: consequently there is no parallel.
Reply to Objection 2. The sacrament of Baptism is accomplished in the use of the matter, and consequently no one can baptize himself, because the same person cannot be active and passive in a sacrament. Hence neither in this sacrament does the priest consecrate himself, but he consecrates the bread and wine, in which consecration the sacrament is completed. But the use thereof follows the sacrament, and therefore there is no parallel.
Reply to Objection 3. If Christ's body appears miraculously upon the altar under the guise of flesh, or the blood under the guise of blood, it is not to be received. For Jerome says upon Leviticus (cf. De Consecr., dist. 2): "It is lawful to eat of this sacrifice which is wonderfully performed in memory of Christ: but it is not lawful for anyone to eat of that one which Christ offered on the altar of the cross." Nor does the priest transgress on that account, because miraculous events are not subject to human laws. Nevertheless the priest would be well advised to consecrate again and receive the Lord's body and blood.
Source: Summa Theologica (New Advent)