When things get bad, when they won't listen to reason and when their substance abuse is obviously causing them great harm, can you have them involuntarily committed for their own good?
It depends.
Firstly, the law regarding involuntary commitment varies by state and eligibility equipments will differ, but in general, all states do allow for involuntary treatment under certain extreme and urgent situations.
In most cases, the person in question will need to present with recent behaviors that clearly show that they demonstrate an immediate danger to harm themselves or harm others. If they are neglectful to their basic needs to an extent that puts them in immediate harms way, and these needs cannot be met by family, then the state may also intervene.