Doctor who?

Playing with a new iPhone app, which pinpoints the quirky history of London.
The marker today led me to The Old Doctor Butler's Head, one of many pubs in the 17th century that used to serve the doctor's 'purging ale'.
It was made of a concoction of laxatives, including senna, liquorice and scurvy grass, according to the site.
The doc had no medical qualifications, but that didn't hold him back - and I bet the patients couldn't hold back afterwards either!