All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
The fact that your husband stole your Mahr (bridal money) does not invalidate the marriage contract. However, your husband is obligated to repent to Allah Almighty from theft and return your bridal money to you. He is also obligated to repent to Allah from buying drugs, as they are extremely forbidden and one of the greatest evils and mother of all evils.
It is permissible for you to take his case to the court so that the judge will oblige him to return your Mahr, and it is also permissible for you to ask for divorce because of his committing this major sin.
Nonetheless, what we advise you to do is to strive hard to turn your husband into a righteous man and help him to repent from these evils; among the means for achieving this is that he should avoid keeping company with corrupt people, be keen on keeping company with the righteous people, listen to influential lectures, and occupy his time with beneficial deeds.
Allah Knows best.