I am going to disagree a little here. A parent is not required to medicate their child for ADHD. It is not legally medical neglect if a parent chooses not to medicate their child for ADHD. Yes, it will thoroughly tick off school officials if they do not, but they cannot lose custody over that decision.
Now, this is not a parent who has chosen not to medicate the child, it is a parent who currently does not have the financial ability to pay for the meds. However, I don't think that changes the legal status.
Also, a doctor would not insist on a child being on meds for ADHD. A doctor would go with the parent's wishes if the doctor agreed that the child had ADHD. Therefore a parent would not be going against doctor's orders if the parent chose not to medicate their child.