Belief still has an effect on health, we just call it something else now: the placebo effect. There were also false correlations, where someone got better, but the treatment had nothing to do with the recovery. We have better conceptual tools to screen for them, but we still have some “treatments” that may be due to false correlations.
Medicine is still kind of a crap-shoot. Many — if not most — branded medicines exploit the placebo effect to boost their outcomes, which are sometimes not statistically significant relative to a sugar pill. Many medicines pharmaceutical companies spend so much time and money developing are barely more effective in treating a disease state than nothing, and yet have side effects that can significantly impact whatever quality of life the patient has left. (Read Ben Goldacre’s Bad Science or Bad Pharma for an accessible treatment of how medical trials are manipulated or buried.)
SSRIs, for example, come out about equal to effectiveness in treating depression to a placebo, but also have common serious side effects like suicidal ideation (ironic, given that they’re supposed to be treating depression, which makes people contemplate suicide), sexual dysfunction, and weight gain. Check out recent meta-studies of SSRIs for confirmation. Not only do we still not have a clear idea of what they actually do (there are only unproven theories as to the mechanism) but they don’t perform the function they were developed for. We might just as well be treating some conditions, particularly psychological ones, with [chants and rattles](We might as well be treating some things with [url=Feasibility and short-term outcomes of a shamanic treatment for temporomandibular joint disorders - PubMed) as medications.
A few Radio Lab shorts I’ve listened to come to mind when talking about medical treatments. The most recent one was about rabies and talked about how the Milwaukee protocol may — or may not — have been effective in saving a girl from rabies. As usual, there are links to more reading on the site, but basically they found out that the girl fit a genetic profile for resistance to rabies and unfortunately the treatment probably isn’t generalizable for all populations. Also, the actual protocol may not have had much to do with her recovery. The jury is still out on whether it’s the 21st century version of the application of a cock’s anus to a bite wound or not.
There were earlier ones about the effectiveness of the Heimlich maneuver (The technique is now considered of questionable use, he made claims that it cured things it could not possibly affect, and Heimlich proposed some “treatments” for cancer and AIDS later on in life that are undeniably screwy) and what physicians think about medical interventions (They’re very strongly against anything but pain management, calling feeding tubes torture, and resuscitation most effective for giving you a brain-dead body to hook up to machines, but useless for a good outcome).
Ask physicians, and most of them will tell you that there are four things in medicine that have saved countless lives: sterile technique, anesthesia, pain management, and the germ theory of disease, which led to vaccines and antibiotics. That’s not to say that there are no modern innovations, but that these four have had the biggest impact on health in the past, and are almost equally as important now as they were when they were first introduced, a century or more ago.
The first three, sterile technique, anesthesia, and pain management, made surgical interventions possible. Without them, surgery would be horrible butchery on a conscious and very distressed person, and would still offer almost no likelihood of recovery. Even with adherence to strict cleanliness procedures and prophylactic application of antibiotics now, there are still a non-zero number of patients who have complications from infection or sepsis post-surgery.
Honestly, the more we find out about the way bodies work, the more mysteries we find. Why does the placebo effect even exist? How many things we think of as chronic diseases are actually infections? Ulcers used to be thought to be caused by stress. They’re mostly caused by bacteria. How many health problems are caused by a modern lifestyle? Allergies might be an overreaction by the immune system to a lack of infection and injury. Systemic inflammation, probably from our food choices is a major factor in heart disease and some metabolic disorders.
In some areas, we’re a good bit above shaman healing, but in others we’re damn near as primitive. I guarantee that in 100 years, people will look back at what medicine is doing right now and scoff at the idiots who thought X could ever cure syndrome Y when it’s clearly Z that causes it, and not A.