From Pope St. John Paul II’s encyclical Veritatis Splendor (1993):

As is evident, in the question of the morality of human acts, and in particular the question of whether there exist intrinsically evil acts, we find ourselves faced with the question of man himself, of his truth and of the moral consequences flowing from that truth. By acknowledging and teaching the existence of intrinsic evil in given human acts, the Church remains faithful to the integral truth about man; she thus respects and promotes man in his dignity and vocation. Consequently, she must reject the theories set forth above, which contradict this truth.

Dear Brothers in the Episcopate, we must not be content merely to warn the faithful about the errors and dangers of certain ethical theories. We must first of all show the inviting splendour of that truth which is Jesus Christ himself. In him, who is the Truth (cf. Jn 14:6), man can understand fully and live perfectly, through his good actions, his vocation to freedom in obedience to the divine law summarized in the commandment of love of God and neighbour. And this is what takes place through the gift of the Holy Spirit, the Spirit of truth, of freedom and of love: in him we are enabled to interiorize the law, to receive it and to live it as the motivating force of true personal freedom: “the perfect law, the law of liberty” (Jas 1:25).

— Veritatis Splendor 83