Actually, they do know it works. It may not always work (same as any medication, there are no 100% effective treatments for any condition) Some are arguing it shouldn't be used at all because there are segments of the population who it shouldn't be used for, because there are contraindications. But that is true of any medication. The contraindications and safe doses are already known because it is already been approved and tested for treatment of malaria. The ideal dosage for the off label usage is not yet known (but again, safe dosage is). So it can already be safely prescribed if the doctor takes note of whether or not the patient has contraindications for it. It is not THE solution, but it definitely adds a tool that doctors can use.