I'd always believed that Aztec Sweet Herb (formerly, Lippia dulcis, now Phyla scabberima), the source of the sugarless sweetener hernandulcin, also contains significant amounts of the toxic substance camphor, and thus should only be consumed in small amounts, and in particular be avoided by pregnant women. However, I just ran into this interesting paper from 1996:
https://www.sciencedirect.com/science/article/pii/S0031942296006917Apparently the first studies of the plant involved samples collected in Tlayacapan (where they're known for use in treating dysentery and abdominal inflamation), and they identified hernandulcin as the sweetening compound, in significant quantities. A followup study involved a mixture of plants collected in Tlayacapan and herbs purchased in Mexico City, being sold as an abortifacent. They strangely found little hernandulcin (although their analysis method may have been to blame), but also found that the essential oil was 53% camphor, creating the health concerns. This study here analyzed plants collected in Orocovis, Puerto Rico and found ample hernandulcin (36% of the essential oil) and no camphor whatsoever. It also yielded much higher essential oil contents than the Mexican plants had. In Puerto Rico - and, from what we know of the Aztecs' usage of the herb - there were no abortifacent properties attributed to it. The author suggests several possibilities, but perhaps the most probable is that the abortifacent-variant sold in Mexico was misidentified and was not L. dulcis / P. scabberima. It might also answer the paradox of how you could have a sweet-tasting herb containing so much camphor, as camphor is bitter tasting.
I need to research this some more later, but I'll call this good news for fans of natural sugarless sweeteners