I would suggest you not to separate from your wife immediately, try to give her some time to get over from her addiction. Addiction is defined as a chronic, relapsing disorder characterized by compulsive drug seeking and use despite adverse consequences. † It is considered a brain disorder because it involves functional changes to brain circuits involved in reward, stress, and self-control. Addiction is not something that can be cured in a week or so, therefore, you have to give her some time. Try to talk to your wife about rehab centers. Try to convince her to go to a drug rehab center. Wait for her to recover fully and after that, if you still find out that she is again using drugs, then you can opt for a divorce.
Divorce under Hindu law is divided into two types:
Mutual Divorce: Under the Hindu Marriage Act, divorce by consent is governed by Section 13-B. As the name suggests, in an amicable divorce, both parties, i.e. husband and wife, agree on a peaceful separation and give their consent. The husband and wife must settle the issues regarding maintenance and custody of the children, if any, in advance. There are only two requirements for filing for a divorce by mutual consent: Firstly, both parties must agree and secondly, they must have lived separately for at least one year
Contested divorce: If the divorce is initiated by either of the spouses, it is called a contested divorce. Section 13 of the Hindu Marriage Act, 1955, lists the grounds for filing a contested divorce, including cruelty, change of religion, insanity, communicable diseases or that one of the spouses has not been seen for more than seven years.
You can apply for divorce under the grounds of:
1. Adultery.
2. Desertion.
3. Insanity.
4. Conversion.
5. Renunciation.
6. Cruelty.
7. Venereal disease.
8. Presumption of death.
9. Sodomy,
10. Bestiality,
11. Bigamy,
12. Conviction for an offense of moral turpitude such as Rape
As you said your wife is a drug addict, then, you can appeal for a divorce under the grounds of Insanity. As she is a drug addict that means she is not mentally stable and you can easily separate from her. And you can easily get the custody of your kids as she is mentally unstable and not safe for the kids.