Hi, sorry to hear about the situation you are in.
This is not 100% but from what i know, if you can prove there is a vaild reason for you to contest his application for custardy, (ie I think drug use is a very good reason!) then yes he would still have to pay child support, but would not be able to have access to your child. He would have to still give you some financial assistance in the form of child support, but because of his past issues, may very well be judged to be an unsuitable person to have any access rights.
i would also advise you to keep a diary of any contact he might make along with what was said each time. Things like that can come in very handy if you kept them up to date. Also i realsie this may sound a little devious, but if you have any evidence that he is unfit, keep it and make sure you present it to the necessray people to influence their decision.
hope this helps a little - good luck!