Can a child be taken away from its parents for drugs ?

The court would probably require drug testing on a petition for change of custody, and if the mother fails a drug test, the court would probably change custody from the mother to the father, if he offers himself as a fit parent with a good home environment. This could also lead to DFCS action against the mother in juvenile court as well.

This is definitely grounds for a modification of custody for dad to ask the court to change custody. If the admissions about drug use are in writing (text, email, etc.) they can certainly be used as evidence. Depending on the age of the child, a judge may talk to him/her, or may appoint a guardian ad litem. If he is intending on filing a petition for change of custody on these grounds, he'd likely want to seek drug testing in court as soon as possible.

It certainly could be grounds for a custody modification. You should consult with an attorney who review the facts of the case in detail and help you plan the proper course of action to address the situation.