The Regency was at the cusp of modern medicine. The Leeches no longer quite believed in the humor theory, but didn't have anything to replace it with. This makes for interesting quandaries.
In what I'm currently writing, "the French Orphan", the young heroine (Henriette) uses "blue vitriol" (copper sulfate) as one of the magic ingredients in her fomentations and on bandages. This actually was used in veterinary medicine until recently as an antiseptic, and would have been something a cow farmer's granddaughter would use. She's also a bit more picky about cleanliness than the human doctors, which is something that would make the difference between a successful cattle farmer and one that just barely makes it. Of course she has no idea why doing these things is important, it's just what her family did.
While this is a little fantastic to the modern ear - my grandmother used Mercurochrome (a mercury salt) as an antiseptic and my husband swears by tincture of iodine.
The "real" doctors of the time would make up custom prescriptions based on whatever seemed right. Nothing was ever tested, but then everything was organic - so I suppose it was "safe". I remember reading about "Holloway's pills", which were these little chalky miracle drugs from the 1830's-1890's. They were literally chalk and herbs, but they made Mr. Holloway extremely rich. What is truly weird is this was his second attempt. His first, a skin cream for rashes, actually had active ingredients in it and would have worked for minor problems. He couldn't give it away!
There wasn't any real licensing so Henriette as well qualified as the various leeches, and probably would have caused a lot less harm.