When a child struggles with substance or other behavior problems, communication often breaks down between the adults who love that child.* Most people struggle to not get defensive or lose their cool in situations they don’t understand or know how to control, and it’s not uncommon for parents to feel at wits’ end with each other when their child is doing risky, upsetting things. Disagreements are understandable. After all, misalignment can easily happen in the best of circumstances over lower-stakes issues like bedtime and vegetables; the more serious the issue, the more polarizing it can be. But helping depends in no small part on finding a way to collaborate with your co-parent (and anyone else involved in raising your child).
As you try to help your child change their relationship with substances, it will be important for every adult involved to give clear directions and consistent consequences (positive and negative). Change, even change for the better, is difficult and your child will feel ambivalent about it. It will be hard for her to make different friends, or not be high at parties, or leave earlier than other kids. The more ambivalent she is, the more important it is for you to make your expectations clear. Different expectations (explicit or implied) between you and your partner amount to mixed messages for your child.
Additionally, the more agreement you can reach with your partner, the less stressed you will each feel and the happier you will both be. And with less conflict and stress in general you can, in turn, be more positive with your child.
Alignment and collaboration with your partner doesn’t mean across-the-board, united-front agreement on “the party line,” especially with older children. Children over sixteen live in the adult world enough to know that uniform agreement is not realistic. Alignment can mean understanding what you agree on, what you don’t agree on, and what the “policy” is in any case (“Your father and I have a somewhat different feeling about this, but we’ve decided it’s important for you to be home by midnight”). You can acknowledge differences and still align your expectations.