The basic principle is that it is not permissible for a woman to ask for divorce unless there is a reason for that. The Messenger of Allaah (Peace And Blessings Of Allaah Be Upon Him) said: "Any woman who asks her husband for a divorce with no reason, the fragrance of Paradise will be forbidden to her." Narrated by Ahmad (21874), Abu Dawood (2226) and al-Tirmidhi (1187); classed as saheeh by al-Albaani in Irwa' al-Ghaleel (2035).

And the words "with no reason" mean without there being any hardship that compels her to ask for a divorce.

Al-Haafiz Ibn Hajar (may Allaah have mercy on him) said in Fath al-Baari:

The reports which warn women against asking for divorce from their husbands are to be understood as applying to cases where there is no reason for that, because of the hadeeth of Thawbaan… then he mentioned the hadeeth quoted above. End quote.

Undoubtedly addiction to drugs is a serious shortcoming, which harms a woman in both religious and worldly terms, because there is no guarantee that her husband will not enter upon her when he is intoxicated and beat her or revile her, or ask her to do something at that time which it is not permissible for her to do.

Such a thing is regarded as an excuse which makes it permissible for a woman to ask for divorce, but what the woman should do is be patient with her husband, and try to set him straight as much as she can. If she is not able to do that, and she finds that staying with him will cause her harm, then there is nothing wrong with asking for divorce in that case.

Shaykh Muhammad ibn 'Uthaymeen (may Allaah have mercy on him) was asked:

What is the ruling on a woman seeking divorce from her husband who uses drugs? What is the ruling on her staying with him? Please note that there is no one who will provide for her and her children except him.

He replied:

It is permissible for a woman to ask for a divorce from her husband who is addicted to drugs, because her husband's condition is not acceptable. In this case, if she asks for a divorce from him, then the children should stay with her, if they are younger than seven years, and the father must spend on them. If she can stay with him to set him straight by advising him, then that is better. End quote.

Fataawa al-Mar'ah al-Muslimah (2/745, 746).

And Allaah knows best.