I'm a little surprised no one's brought this up, as I
know there are folks who frequent this board that know this ...
Deer Tongue was commonly used as a condiment in pipe tobacco, particularly American blends, up until the early 1990s. Carter Hall, for example, contained Deer Tongue as a condiment. The predominant flavoring in Deer Tongue is coumarin, which as an extract itself was used as a flavoring in pipe tobacco and cigarettes. I'm not certain whether Captain Black (Regular) contained Deer Tongue
per se, but CB used a pretty heavy amount of coumarin to contribute to its vanilla flavoring (these figures used to be more easily found via search engine than they are now).
Coumarin is mildly toxic to the kidneys and liver, was banned in the US in the mid 1950s as a food additive; big tobacco stopped using it as a flavoring in cigarettes in the mid 1980s and manufacturers of OTC blends more or less stopped using it as a flavoring in the early 1990s (though, supposedly, the unmodified form of coumarin occurring naturally in Deer Tongue is less harmful).
Anyone who knows about this in greater detail care to chime in? :
: