Sheikh `Abd al-Rahmân al-`Ajlân, lecturer at the Grand Mosque in Mecca
It is unlawful for a Muslim to drink alcoholic beverages or to take any intoxicating substance. It is a great sin in Islam to drink or take drugs, and it can lead to other evil behaviors. People who are intoxicated lose their inhibitions ad good judgment which can lead them to fall in adultery, theft, murder, and other despicable acts.
It is the obligation of any Muslim who falls into the sin of imbibing alcoholic beverages or taking drugs to abandon the practice and hasten to Allah in repentance. Repentance requires a sincere sense of regret on the part of the penitent person as well as a firm resolve never to return to the sin.
The person should also refrain from confessing to other people a sin that Allah has concealed. Allah forgives those who are sincere to Him in their repentance.
If a person who drank or took drugs the night before wakes up sober and clear-minded during the day in Ramadan, then that person's fast is intact.
If, however, the person wakes up during the day still fully inebriated and incoherent, then that person will have to make up that day of fasting later on.
And Allah knows best.
Source: Islam Today