The Kitáb-i-Aqdas - The Most Holy Book
Index term: Alcohol
k119.
It is inadmissible that man, who hath been endowed with reason, should consume that which stealeth it away. Nay, rather it behoveth him to comport himself in a manner worthy of the human station, and not in accordance with the misdeeds of every heedless and wavering soul.
n144.
It is inadmissible that man, who hath been endowed with reason, should consume that which stealeth it away.
There are many references in the Bahá'í Writings which prohibit the use of wine and other intoxicating drinks and which describe the deleterious effect of such intoxicants on the individual. In one of His Tablets, Bahá'u'lláh states:

Beware lest ye exchange the Wine of God for your own wine, for it will stupefy your minds, and turn your faces away from the Countenance of God, the All-Glorious, the Peerless, the Inaccessible. Approach it not, for it hath been forbidden unto you by the behest of God, the Exalted, the Almighty.

'Abdu'l-Bahá explains that the Aqdas prohibits "both light and strong drinks", and He states that the reason for prohibiting the use of alcoholic drinks is because "alcohol leadeth the mind astray and causeth the weakening of the body".
Shoghi Effendi, in letters written on his behalf, states that this prohibition includes not only the consumption of wine but of "everything that deranges the mind", and he clarifies that the use of alcohol is permitted only when it constitutes part of a medical treatment which is implemented "under the advice of a competent and conscientious physician, who may have to prescribe it for the cure of some special ailment".
n170.
the use of opium . . . any substance that induceth sluggishness and torpor
This prohibition of the use of opium is reiterated by Bahá'u'lláh in the final paragraph of the Kitáb-i-Aqdas. In this connection, Shoghi Effendi stated that one of the requirements for "a chaste and holy life" is "total abstinence . . . from opium, and from similar habit-forming drugs". Heroin, hashish and other derivatives of cannabis such as marijuana, as well as hallucinogenic agents such as LSD, peyote and similar substances, are regarded as falling under this prohibition.
'Abdu'l-Bahá has written:

As to opium, it is foul and accursed. God protect us from the punishment He inflicteth on the user. According to the explicit Text of the Most Holy Book, it is forbidden, and its use is utterly condemned. Reason showeth that smoking opium is a kind of insanity, and experience attesteth that the user is completely cut off from the human kingdom. May God protect all against the perpetration of an act so hideous as this, an act which layeth in ruins the very foundation of what it is to be human, and which causeth the user to be dispossessed for ever and ever. For opium fasteneth on the soul so that the user's conscience dieth, his mind is blotted away, his perceptions are eroded. It turneth the living into the dead. It quencheth the natural heat. No greater harm can be conceived than that which opium inflicteth. Fortunate are they who never even speak the name of it; then think how wretched is the user.
O ye lovers of God! In this, the cycle of Almighty God, violence and force, constraint and oppression, are one and all condemned. It is, however, mandatory that the use of opium be prevented by any means whatsoever, that perchance the human race may be delivered from this most powerful of plagues. And otherwise, woe and misery to whoso falleth short of his duty to his Lord.


In one of His Tablets 'Abdu'l-Bahá has stated concerning opium: "the user, the buyer and the seller are all deprived of the bounty and grace of God".
In yet another Tablet, 'Abdu'l-Bahá has written:

Regarding hashish you have pointed out that some Persians have become habituated to its use. Gracious God! This is the worst of all intoxicants, and its prohibition is explicitly revealed. Its use causeth the disintegration of thought and the complete torpor of the soul. How could anyone seek the fruit of the infernal tree, and by partaking of it, be led to exemplify the qualities of a monster? How could one use this forbidden drug, and thus deprive himself of the blessings of the All-Merciful?
Alcohol consumeth the mind and causeth man to commit acts of absurdity, but this opium, this foul fruit of the infernal tree, and this wicked hashish extinguish the mind, freeze the spirit, petrify the soul, waste the body and leave man frustrated and lost.


It should be noted that the above prohibition against taking certain classes of drugs does not forbid their use when prescribed by qualified physicians as part of a medical treatment.