Romans had contraceptive herb - any truth?

Last night a friend of mine claimed that the Romans had a medicinal herb that was a nearly 100% effective contraceptive when taken daily, and that this herb was in such great demand that it became extinct. This seems unlikely to me, especially since the friend in question has a tendancy to spread wildly implausible urban legends.

Is there any truth to her claim? Anyone ever hear this one before?

Silphium or Pennyroyal:
Birth Control in Antiquity

Whodathunkit. She was right this time. You learn something new every day.

Not sure about a herb driven to extinction, but herbal contraceptives and abortificants have been around a while.
It’s also interesting to note that our current hormonal contraceptive pill orignally derived from the Mexican yam.