Osteopathy and any other placebo can be effective in curing illness, but only if the illness is a psychosomatic one. Placebos are a panacea for psychosomatic disorders, but completely worthless otherwise. This is why so many people swear that osteopathy has cured them: The ailment was all in their head, and they believed the snake-oil purveyor would heal them, so they got better.
I know someone who believed he had joint pain due to arthritis, which was cured by inserting copper plates in his shoes. He couldn’t explain the causality for such a cure, “but it really works!” It was a perfect cure until he actually developed real arthritis, which did not respond at all to the copper miracle cure.
Insurance companies and medicare should drop all funding of pseudo-scientific “treatments” such as osteopathy, homeopathy, and chiropracty until such time as clinical trials prove that they work, which will never happen.