Do you know any curious examples that I could look into? Any weird ones? How was this advertising received? Did people actually believe in tonics?
Thank you very much in advance.
I don't know if you meant in America or in Britain, but I know that Duke has a great digitized online collection of early American advertisements (1850 onward, mostly). LINK HERE.
If you meant in the UK, then here is a link of a digital collection from their National Archives. LINK HERE
EDIT: is actually a classroom plan, but includes a collection of primary documents, so whatever.
Enjoy browsing!