Is barley beer (Birch/Barbican) halal or haram, especially if it treats some health problems?

The ruling on whether a drink is permissible or forbidden depends on its contents. If it is neither intoxicating nor harmful, there is no objection to consuming it, because the basic principle regarding drinks is permissibility. Nothing is forbidden among them except what is proven to be harmful or intoxicating. If a drink is intoxicating, it is not permissible to drink any of it, even a small amount.