Earlier quoted context omitted.
ISTR that seaweed was a folk remedy for goiter. It contains relatively high amounts of iodine, which prevents thyroid conditions. I also vaguely recall that the doctrine of signatures wasn't a complete and abject failure, but some cursory Googling indicates that maybe it was after all.
Is that an example from the 15th century? Is there nothing more modern?
Effective treatments as been subsumed into "mainstream" medicine, perhaps with a bit of purification/standardization along the way, while the ineffective and unproven stuff remains "alternative medicine".
If it somehow turns out that homeopathy is an effective therapy for something (besides dehydration), it'll end up with a procedure code, the hospital pharmacy will stock 10x tincture of whatever, and eventually it will be just another mainstream medical treatment.