Many people don't consider substance abuse to be something that psychology should treat, but it can be. Drug addiction and alcoholism may have physical components, but there's often an underlying psychological problem that triggers the abuse. Even overeating may be partly psychological.
Mental health care still suffers a stigma in our society, so it's often not covered at the same level as other health problems. If you or a family member needs psychology help, check your insurance policy carefully. You may find that mental health care is capped at an unreasonable level, or that the reimbursement is minimal.