All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
The use of drugs is among the gravest prohibitions and is considered a major sin, even one of the most reprehensible. It is measured against the prohibition of alcohol, the prohibition of which is established in the Qur'an, Sunnah, and scholarly consensus. The reason for the prohibition of alcohol, the impairment of the mind, is also present in drugs, so they take on the ruling of prohibition similar to that of alcohol. Imam al-Nawawi, may Allah have mercy on him, said: "As for that which causes the mind to be impaired other than drinks and medicines, like bhang (cannabis) and other well-known substances, its ruling is the same as that of alcohol in terms of prohibition. It necessitates making up missed prayers, and there is a punishment for it, but not the prescribed legal punishment (hadd). And Allah the Almighty knows best." [Al-Majmu' Sharh al-Muhadhdhab, Vol. 3/Page 8].
Among the evidences prohibiting alcohol are: " O ye who believe! Intoxicants and gambling, (dedication of) stones, and (divination by) arrows, are an abomination,- of Satan’s handwork: eschew such (abomination), that ye may prosper." {Al-Mai`dah, 90}. The Messenger of Allah (PBUH) said: "Every intoxicant is Khamr and every intoxicant is unlawful." {Transmitted by Bukhari}. Also, Umm Salama told that God’s Messenger forbade every intoxicant and everything which produces languidness. {Transmitted by Abu Dawud}.
Sheikh al-Islam Ibn Hajar al-Asqalani, may Allah have mercy on him, said: "It is deduced from his general statement, "Every intoxicant is prohibited," the prohibition of anything that causes intoxication, even if it is not in the form of a drink. This includes substances like hashish and others. Al-Nawawi and others have affirmed that it is intoxicating while others assert that it is a narcotic-this latter view is a bit stubborn-because it produces effects similar to alcohol in terms of pleasure, ecstasy, habitual use, and indulgence. Even if we tentatively acknowledged that it is not strictly an intoxicant, it has been established in Abu Dawood that there is a prohibition of every intoxicant and everything that causes intoxication, and Allah the Almighty knows best" [Fath al-Bari, Vol. 10/P.45]. Al-Hafiz Ibn Hajar commented on the hadith of Umm Salama narrated by Abu Dawood, saying: "The hadith of Umm Salama is reported by Abu Dawood with a sound chain and the wording is, 'He prohibited every intoxicant and everything that causes intoxication'" [Fath al-Bari, Vol. 10/P.44].
It is obligatory for those afflicted with intoxicants or drugs to quit them immediately and seek the assistance of medical specialists to overcome the withdrawal symptoms that accompany quitting. Imam al-Shurunbulali, may Allah have mercy on him, said: "Indeed, it is obligatory for the one afflicted with drugs to strive to eliminate the need for them, either by using remedies against them or by gradually reducing their use until reaching a point where abandoning them does not harm him." [Hashiyat al-Shurunbulali on Al-Tuhfah, Vol. 9/P.168]. "As for those who are unable to completely quit drug use and rid themselves of its effects, they are sinful and disobedient. Sheikh al-Islam Imam Ibn Hajar al-Haytami, may Allah have mercy on him, said: "It is obligatory for those who have used drugs to gradually reduce their consumption bit by bit. Gradual reduction is a method to wean the liver off its desire for it until quitting does not harm them. This is a consensus we have seen among reputable doctors. If they do not strive for this gradual reduction, then they are sinful, disobedient, and have no excuse'" [Tuhfat al-Muhtaj, Vol. 9/P.168].
Whoever needs a drug for medical treatment, such as a tranquilizer during surgeries to avoid feeling the pain of the incision or amputation, it is permissible to use it to dull the senses. The scholar Sulaiman al-Jamal, may Allah have mercy on him, said: "If there is a need for cutting something like a cyst, a gland between the skin and flesh, or a decaying hand that necessitates the removal of the person's consciousness, using something like anesthesia is permissible, not a liquid intoxicant." [Hashiyat al-Jamal on Sharh al-Minhaj, Vol. 5/P.158].
Regarding someone who consumes a substance from these drugs and remains fully conscious and mentally aware, this person is not considered intoxicated. If they perform the prayer correctly, fulfilling its prescribed conditions and pillars, then their prayer is valid.
The meaning of the validity of his prayer is that he is not required to repeat it or make up for it. However, as for the reward of the prayer, it is not confirmed for him. This is based on the hadith of the Prophet Mohammad (peace be upon him): "If a man among my Ummah drinks Khamr, Allah will not accept his Salah for forty days." {Reported by al-Nasai}.
Sheikh al-Islam al-Nawawi, may Allah have mercy on him, commented on this by saying: "As for the non-acceptance of his prayer, it means there is no reward for it, even though it is sufficient for the obligation to be lifted from him, and does not need to repeat it." [Sharh Sahih Muslim, Vol. 14/P. 227].
As for someone who prays while being in a state of cognitive impairment due to the consumption of drugs, his prayer is not valid. He is obligated to repeat the prayer after regaining his mental faculties if he does so before the end of its designated time. If not, he must make up for it. This is because ablution (wudu) is invalidated by the loss of consciousness, and the worshiper in this state is unaware of what he is doing in his prayer.
Imam al-Khatib al-Shirbini, a Shafi'i scholar, may Allah have mercy on him, said: "One who got drunk intentionally is obligated to make up for the missed prayers because of this act of misconduct. In contrast, if he drank an intoxicant unintentionally or was forced to drink it, he isn`t obligated to make up for the missed prayers. [Moghni al-Mohtaj, Vol. 1/P.314].
In conclusion, if someone consumes drugs but does not lose his mental awareness and prays, his prayer is valid. However, if his mental faculties are impaired due to drugs and he prays while in that state, his prayer is not valid, and he is obligated to repeat it or make up for it. And Allah the Almighty knows best.