What is the Catholic Church's view on curses and its’ after-effects?
First of all, there are different types of curses.
For example in the Old Testament , we see God cursing Adam and Eve. In the Gospels we can see Jesus cursing the fig tree.
Here is what the Catholic Encyclopedia has to say on the subject of cursing.
In its popular acceptation cursing is often confounded, especially in the phrase "cursing and swearing", with the use of profane and insulting language; in canon law it sometimes signifies the ban of excommunication pronounced by the Church. In its more common Biblical sense it means the opposite of blessing (cf. Numbers 23:27), and is generally either a threat of the Divine wrath, or its actual visitation, or its prophetic announcement, though occasionally it is a mere petition that calamity may be visited by God on persons or things in requital for wrongdoing. Thus among many other instances we find God cursing the serpent (Genesis 3:14), the earth (Genesis 3:17), and Cain (Genesis 4:11). Similarly Noah curses Chanaan (Genesis 9:25); Josue, him who should build the city of Jericho (Joshua 6:26-27); and in various books of the Old Testament there are long lists of curses against transgressors of the Law (cf. Leviticus 26:14-25; Deuteronomy 27:15, etc.). So, too, in the New Testament, Christ curses the barren fig-tree (Mark 11:14), pronounces his denunciation of woe against the incredulous cities (Matthew 11:21), against the rich, the worldling, the scribes and the Pharisees, and foretells the awful malediction that is to come upon the damned (Matthew 25:41). The word curse is also applied to the victim of expiation for sin (Galatians 3:13), to sins temporal and eternal (Genesis 2:17; Matthew 25:41).
In moral theology, to curse is to call down evil upon God or creatures, rational or irrational, living or dead. St. Thomas treats of it under the name maledictio, and says that imprecation may be made either efficaciously and by way of command, as when made by God, or inefficaciously and as a mere expression of desire. From the fact that we find many instances of curses made by God and his representatives, the Church and the Prophets, it is seen that the act of cursing is not necessarily sinful in itself; like other moral acts it takes its sinful character from the object, the end, and the circumstances. Thus it is always a sin, and the greatest of sins, to curse God, for to do so involves both the irreverence of blasphemy and the malice of hatred of the Divinity. It is likewise blasphemy, and consequently a grievous sin against the Second Commandment, to curse creatures of any kind precisely because they are the work of God. If, however, the imprecation be directed towards irrational creatures not on account of their relation to God, but simply as they are in themselves, the guilt is no greater than that which attaches to vain and idle words, except where grave scandal is given, or the evil wished to the irrational creature cannot be separated from serious loss to a rational creature, as would be the case were one to wish the death of another's horse, or the destruction of his house by fire, for such wishes involved serious violation of charity.
Curses which imply rebellion against Divine Providence, or denial of His goodness or other attributes, such as curses of the weather, the winds, the world, the Christian Faith, are not generally grievous sins, because the full content and implication of such expressions is seldom realized by those who use them. The common imprecations against animate or inanimate objects which cause vexation or pain, those against enterprises which fail of success, so, too, the imprecations that spring from impatience, little outbreaks of anger over petty annoyances, and those spoken lightly, inconsiderately, under sudden impulse or in joke, are, as a rule, only venial sins — the evil being slight and not seriously desired. To call down moral evil upon a rational creature is always illicit, and the same holds good of physical evil, unless it be desired not as evil, but only in so far as it is good, for example, as a punishment for misdeeds, or a means to amendment, or an obstacle to commission of sin; for in such cases the principal intention, as St. Thomas says, is directed per se towards what is good. When, however, evil is wished another precisely because it is evil and with malice prepense, there is always sin, the gravity of which varies with the seriousness of the evil; if it be of considerable magnitude, the sin will be grievous, if of trifling character, the sin will be venial. It is to be noted that merely verbal curses, even without any desire of fulfilment, become grievous sins when uttered against and in the presence of those who are invested with special claims to reverence. A child, therefore, would sin grievously who should curse father, mother, or grandfather, or those who hold the place of parents in his regard, provided he does so to their very face, even though he does this merely with the lips and not with the heart. Such an act is a serious violation of the virtue of piety. Between other degrees of kindred verbal curses are forbidden only under pain of venial sin. To curse the devil is not of itself a sin; to curse the dead is not ordinarily a grievous sin, because no serious injury is done them, but to curse the saints or holy things, as the sacraments, is generally blasphemy, as their relation to God is generally perceived.
Curses can have very serious effects on both people and animal!
I like to recall the phrase that an exorcist once told when we were discussing the topic of cursing and malediction: ”Be careful what you pray for. Both good and evil could be answered in a way you could regret. People should not wish true evil on others. After all the Devil can hear those curses!”
2 Be not rash with thy mouth, and let not thine heart be hasty to utter any thing before God: for God is in heaven, and thou upon earth: therefore let thy words be few. - Ecclesiastes 5:2
Holiness is in the power of tongue.
Malediction in the form of hurling epithets is not as simple as it may at first appear, however. There is, for example, a fundamental difference between the utterances “You bastard!” and “Go to hell!” The first expresses malevolence or ill will, with reference to an imputed personal characteristic that bespeaks illegitimacy. The second, as watered-down and secularized as it may be in colloquial usage, refers to a supernatural and cosmological domain that remains deeply resonant across religious traditions and even in secular settings. In short, the malediction “You bastard!” is an insult. The malediction “Go to hell!” is a curse. The difference is not only one of degree, but one of kind.
Fr. Gabriele Amorth S.S.P. (1 May 1925 – 16 September 2016), the major exorcist of Rome stated several times in his books, An Exorcist Tells His Story and An Exorcist: More Stories demonstrates that cursing someone may, but not always lead to diabolic possession by the Demon.
Here is how St. Thomas Aquinas answers the question: Whether it is lawful to curse anyone?:
To curse [maledicere] is the same as to speak ill [malum dicere]. Now "speaking" has a threefold relation to the thing spoken. First, by way of assertion, as when a thing is expressed in the indicative mood: in this way "maledicere" signifies simply to tell someone of another's evil, and this pertains to backbiting, wherefore tellers of evil [maledici] are sometimes called backbiters. Secondly, speaking is related to the thing spoken, by way of cause, and this belongs to God first and foremost, since He made all things by His word, according to Psalm 32:9, "He spoke and they were made"; while secondarily it belongs to man, who, by his word, commands others and thus moves them to do something: it is for this purpose that we employ verbs in the imperative mood. Thirdly, "speaking" is related to the thing spoken by expressing the sentiments of one who desires that which is expressed in words; and for this purpose we employ the verb in the optative mood.
Accordingly we may omit the first kind of evil speaking which is by way of simple assertion of evil, and consider the other two kinds. And here we must observe that to do something and to will it are consequent on one another in the matter of goodness and wickedness, as shown above (I-II:20:3). Hence in these two ways of evil speaking, by way of command and by way of desire, there is the same aspect of lawfulness and unlawfulness, for if a man commands or desires another's evil, as evil, being intent on the evil itself, then evil speaking will be unlawful in both ways, and this is what is meant by cursing. On the other hand if a man commands or desires another's evil under the aspect of good, it is lawful; and it may be called cursing, not strictly speaking, but accidentally, because the chief intention of the speaker is directed not to evil but to good.
Now evil may be spoken, by commanding or desiring it, under the aspect of a twofold good. Sometimes under the aspect of just, and thus a judge lawfully curses a man whom he condemns to a just penalty: thus too the Church curses by pronouncing anathema. On the same way the prophets in the Scriptures sometimes call down evils on sinners, as though conforming their will to Divine justice, although such like imprecation may be taken by way of foretelling. Sometimes evil is spoken under the aspect of useful, as when one wishes a sinner to suffer sickness or hindrance of some kind, either that he may himself reform, or at least that he may cease from harming others.
Here follows most causes of demonic possession as recognized by the Church:
Causes of Demonic Possession
According to the Catholic Church, the chief causes of possession are the following:
• making a Pact with the Devil or Demons
• participating in occult or spiritualist rites, including playing with divination devices such as a Ouija™ or doing automatic writing
• offering or dedicating a child to Satan
• being the victim of a witchcraft spell or Curse
Engaging in these activities, as well as leading a deliberately sinful life, give Demons the right and license to take up residence, according to the church. Mental illnesses such as schizophrenia and multiple personality disorder are not considered to be caused by Demonic possession.
The church teaches that God allows possession to happen for a variety of reasons:
• to Demonstrate the truth of the Catholic faith
• to punish sinners
• to confer spiritual benefits through lessons
• to produce teachings for humanity