I'm not quite sure what you mean by "evaluating the effectiveness." Historians generally aren't in the business of judging the remedies of the past as potential cures for the modern world. You might say that the placebo effect is the default assumption. The general belief among medievalists, for example, is that cures would only be written down (or described as being used by someone) if people believed they worked. So, from medieval people's point of view, even something like placing a scrap of a saint's life story in an amulet (like a locket or some such) and having the sick person wear it, might be a functional remedy. They believed it worked, which meant they probably saw some people given that cure who got better (in the face of expectations to the contrary for the disease or injury untreated).

So when modern scholars judge whether cures of the past might be suitable for today, they don't look to premodern evidence. Instead, they apply modern knowledge to different elements of the cure. For example, when we read that wine or honey was used to cleanse the stump of an amputated limb, modern people would say, "We know today that wine/honey/etc has antibacterial properties." Or in the case of my above example of essentially invoking magic, "Yup, placebo effect."

Medieval people didn't have the scientific proof we do, but they did have custom, and custom built on a belief that it worked (in the sense of being better than nothing).