Please forgive the unconscionably long time it has taken me to get back to you, but I wasn’t familiar with the plant you mentioned and needed to do a little research.

Bitter vetch or heath pea (Lathyrus linifolius or Lathyrus montanus)
is not on our medieval plant list (compiled from many sources over many years) and has not been grown here at The Cloisters, nor could I find it in any of the standard references on medieval medicinal plants.

I did find some references online. Bitter vetch seems to have gotten a lot of attention in the U.K. press in recent years as a possible aid in weight loss. This member of the pea family was among the medicinal plant remains discovered at an archaeological excavation of the fourteenth century Soutra Aisle monastery near Edinburgh.

My guess would be that the use of the heath pea might have been very local. It may not have been used as an appetite suppressant outside of Scotland, although the RHS Index to Garden Plants lists it as native to central and western Europe.

Vetches have been resorted to as famine foods for many centuries.
It may be that the appetite-suppressing property of the bitter vetch was discovered in that way. In any case, I will be looking for more information on medieval usage and documentation, and may well add it to our plant list. Thank you for the lead!

There’s seems to be some disagreement as to whether teasel was formerly used to card wool—i.e, to clean and separate the raw fibers. Its primary use was to raise the nap on woolen cloth once it was woven. I think you probably do have the wild or medicinal one.