The four major vices of Kali-yuga are (1) illicit connection with women, (2) animal slaughter, (3) intoxication, (4) speculative gambling of all sorts.
(Srimad Bhagavatam-----1:1:6-----purport).

Gambling of all description, even speculative business enterprise, is considered to be degrading, and when gambling is encouraged in the state, there is a complete disappearance of truthfulness.
(Srimad Bhagavatam-----1:17:38-----purport).

If we want to drive out corruption from the state, we must first of all organize society to accept the principles of religion, namely austerity, cleanliness, mercy and truthfulness, and to make the condition favorable we must close all places of gambling, drinking, prostitution and falsity.
(Srimad Bhagavatam-----1:17:43-44-----purport).

One who is not a devotee, however, is the most fallen and condemned. It is recommended, therefore, that a chaste wife not associate with a fallen husband. A fallen husband is one who is addicted to the four principles of sinful activity—namely illicit sex, meat-eating, gambling and intoxication.
(Srimad Bhagavatam-----7:11:28-----purport).

The principles of renunciation are four: (1) to avoid illicit sex life, (2) to avoid meat-eating, (3) to avoid intoxication and (4) to avoid gambling. These four principles are called tapasya, or austerity. To absorb the mind in the Supreme in Kṛṣṇa consciousness is the process of spiritual realization.
(Srimad Bhagavatam-----3:20:53-----purport).

At present, for want of Kṛṣṇa consciousness, or God consciousness, the entire world is in darkness, having been covered by the four principles of sinful life—meat-eating, illicit sex, gambling and intoxication.
(Sri Caitanya Caritamrta----1:9:41------purport).

Betel nuts are an intoxicant, and therefore the regulative principles prohibit eating them. Śrī Caitanya Mahāprabhu's pastime of fainting after eating betel nuts is a solid instruction to all of us that one should not touch betel nuts, even those offered to Viṣṇu, just as one should not touch grains on the Ekādaśī day. Of course, Lord Caitanya Mahāprabhu's fainting had a particular purpose. As the Supreme Personality of Godhead, He can do whatever He likes and eat whatever He wants, but we should not imitate His pastimes.
(Sri Caitanya Caritamrta----1:15:16------purport).

What is the use of smoking and drinking tea and coffee? People are already intoxicated by material enjoyment, and if they indulge in further intoxication, what chance is there for self-realization?
(Sri Caitanya Caritamrta----2:7:128------purport).

The mind is always accompanied by six enemies—namely, kāma, krodha, mada, moha, mātsarya and bhaya—that is, lust, anger, intoxication, illusion, envy and fear. Although the mind may be merged in spiritual consciousness, one should always be very careful in dealing with it, just as one is careful in dealing with a snake.
(Sri Caitanya Caritamrta----2:11:10------purport).

In Bhagavad-gītā, First Chapter, illicit sex life is also very much condemned, and it is said that one who produces children by illicit sex life is sent to hell. It is confirmed here in the Bhāgavatam that such offenders are put into hellish conditions of life in Tāmisra, Andha-tāmisra and Raurava.
(Srimad Bhagavatam-----3:30:28-----purport).

The greatest calamity in life is to become godless and therefore sinful. If the state head or king allows the citizens to become sinful by indulging in illicit sex life, intoxication, meat-eating and gambling, then the king is responsible, and he has to suffer the resultant sequence of reactions for the sinful lives of the citizens because he levies taxes on them unnecessarily.
(Srimad Bhagavatam-----4:20:21-----purport).

Irreligious persons are like animals, but in this Kṛṣṇa consciousness movement such persons can come to a sense of understanding things as they are and abandon the four principles of prohibited activities—namely illicit sex life, meat-eating, gambling and intoxication. This is the beginning of religious life.
(Srimad Bhagavatam-----4:26:10-----purport).

Sons and daughters should not be allowed freedom to intermingle with the opposite sex unless they are married. This Vedic social organization is very good in that it stops the promulgation of illicit sex life, or varṇa-saṅkara, which appears under different names in this present day.
(Srimad Bhagavatam-----4:27:8-----purport).

Generally a man should not have sexual relations with any woman other than his wife. According to Vedic principles, the wife of another man is considered one's mother, and sexual relations are strictly forbidden with one's mother, sister and daughter. If one indulges in illicit sexual relations with another man's wife, that activity is considered identical with having sex with one's mother. This act is most sinful. The same principle holds for a woman also; if she enjoys sex with a man other than her husband, the act is tantamount to having sexual relations with her father or son. Illicit sex life is always forbidden, and any man or woman who indulges in it is punished in the manner described in this verse.
(Srimad Bhagavatam-----5:26:20-----purport).

As far as the urges of the genitals are concerned, there are two—proper and improper, or legal and illicit sex. When a man is properly mature, he can marry according to the rules and regulations of the śāstras and use his genitals for begetting nice children. That is legal and religious. Otherwise, he may adopt many artificial means to satisfy the demands of the genitals, and he may not use any restraint. When one indulges in illicit sex life, as defined by the śāstras, either by thinking, planning, talking about or actually having sexual intercourse, or by satisfying the genitals by artificial means, he is caught in the clutches of māyā. These instructions apply not only to householders but also to tyāgīs, or those who are in the renounced order of life.
(Nectar of Instruction).

When the modes of passion and ignorance increase in human society, giving rise to unnecessary economic development, the result is that people become involved with wine, women and gambling. Then, being mad, they maintain big slaughterhouses or occasionally go on pleasure excursions to kill animals. Forgetting that however one may try to maintain the body, the body is subject to birth, death, old age and disease, such foolish rascals engage in sinful activities, one after another.
(Srimad Bhagavatam-----10:10:9-----purport).

There is a certain pattern of behavior prescribed for those actually trying to become perfect. In our Kṛṣṇa consciousness movement we advise our students not to eat meat, not to gamble, not to engage in illicit sex and not to indulge in intoxication. People who indulge in these activities can never become perfect; therefore these regulative principles are for those interested in becoming perfect and going back to Godhead.
(Sri Caitanya Caritamrta----2:19:159------purport).

This is the process of initiation. The disciple must vow that he will no longer commit sinful activity—namely illicit sex, meat-eating, gambling and intoxication. He promises to execute the order of the spiritual master. Then the spiritual master takes care of him and elevates him to spiritual emancipation.
(Sri Caitanya Caritamrta----2:24:256------purport).

If one accepts a poverty-stricken position because of losing money in business, gambling, prostitution or intoxication, no one will praise him, but if one becomes poverty-stricken by giving all of his possessions in charity, he becomes adored all over the world. Aside from this, if a benevolent and merciful person exhibits his pride in becoming poverty-stricken by giving his possessions in charity for good causes, his poverty is a welcome and auspicious sign of a great personality. Bali Mahārāja decided that even though he would become poverty-stricken by giving everything to Vāmanadeva, this is what he would prefer.
(Srimad Bhagavatam-----8:20:10-----purport).

Material life is such that due to indulgence in illicit sex, gambling, intoxication and meat-eating, the conditioned soul is always in a dangerous condition. Meat-eating and intoxication excite the senses more and more, and the conditioned soul falls victim to women.
(Srimad Bhagavatam-----5:14:22-----purport).

If one wants to go to hell by illicit sex, meat-eating, gambling and intoxication, he must acquire so many things. For illicit sex he must arrange for money for brothels, for meat-eating he must arrange for many slaughterhouses, for gambling he must arrange for casinos and hotels, and for intoxication he must open many breweries. Clearly, therefore, if one wants to go to hell he must endeavor very much, but if he wants to return home, back to Godhead, there is no difficult endeavor.
(Srimad Bhagavatam-----7:7:38-----purport).

Simply by hearing, by attending lectures in the different centers of the Kṛṣṇa consciousness movement, where topics of Kṛṣṇa from Bhagavad-gītā and Śrīmad-Bhāgavatam are discussed, they will be purified of their sinful inclination for constant indulgence in illicit sex, meat-eating, intoxication and gambling, which have all become prominent in modern days. Thus they can be raised to the status of light. Puṇya-śravaṇa-kīrtanaḥ. Simply by joining the kīrtana—Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare—and by hearing about Kṛṣṇa from Bhagavad-gītā, one must be purified, especially if he also takes prasāda. This is all going on in the Kṛṣṇa consciousness movement.
(Srimad Bhagavatam-----7:14:3-4-----purport).