Ruling on one who utters words of kufr under the influence of drugs; ruling on marriage of such a person

Firstly: 

Undoubtedly taking drugs is a major sin, because of what it
results in of mischief, enmity and evil. Hence ‘Uthmaan ibn ‘Affaan (may
Allah be pleased with him) said: Avoid khamr, for it is the mother of all
evils.”

Narrated by an-Nasaa’i, 5666; classed as saheeh by al-Albaani 

The word khamr refers to anything that intoxicates, whether
it is alcoholic drinks, drugs or anything else. 

Secondly: 

When a person takes drugs, he either does not lose his mind
altogether, so he is still aware of what he is saying and means it. In this
case if he utters words of kufr then he has become a kaafir, and if he
divorces his wife then his divorce counts as such, because he comes under
the heading of those who are accountable as he is still able to understand
what he is saying and doing; 

Or he is not aware of what he is saying and does not mean it
at all; rather his state of intoxication has overwhelmed him and he was
mumbling when he totally unaware of what he was saying. In this case if he
utters words of kufr he does not become a kaafir, and if he divorces his
wife it does not count as such. 

Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him)
said: 

If the reason that caused him to lose his mind was something
forbidden, the intoxicated person is not excused, although he is not deemed
to be a kaafir according to the more correct of the two opinions, and his
divorce does not count as such according to the more correct of the two
opinions.

End quote from Majmoo‘ al-Fataawa, 10/60 

Ibn al-Qayyim (may Allah have mercy on him) said: 

The one who studies the sources of sharee‘ah will realise
that the Lawgiver disregarded words that were not meant as said by the one
who uttered them; rather he uttered them unintentionally, as in the case of
one who is sleeping, or forgot, or was intoxicated, or was ignorant, or was
compelled, or made a mistake as a result of extreme joy or anger or
sickness, and the like.

End quote from I‘laam al-Muwaqqi‘een, 3/78 

Shaykh Ibn ‘Uthaymeen (may Allah be pleased with him) said:

Words spoken by one who was intoxicated do not count at all,
whether they concerning himself or anyone else, and his actions are like the
actions of one who made a mistake; he is to be taken to task for actions for
which one who made a mistake is to be taken to task, so long as we do not
know that he intended to do this haraam action by consuming the intoxicant.
In that case we regard his actions as being like the actions of one who is
sober and he is to be taken to task for them.

End quote from ash-Sharh al-Mumti‘, 14/444 

See also the answer to question no.
176424 

Thirdly: 

If a person’s apostasy is proven by means of false beliefs,
words or actions, and he was not forced or compelled to do that, and he did
not make a mistake or lose his mind, then he wants to come back to Islam, he
should utter the twin declaration of faith (shahaadatayn), do ghusl and ask
Allah for forgiveness, and he should hasten to do righteous deeds. 

See the answer to question no.
7057,
93027 and
134339 

And Allah knows best.