For the past couple of years, Dunedin herbalist Sandra Clair, originally from Switzerland, has been translating the 16th-century Materia Medica from early high German.
The translation, in which she has now been joined by a German research assistant, will take a lifetime and she plans to seek much more assistance.
The project had influenced how she used the herbs she was familiar with, whose applications had narrowed since the Middle Ages.
Ms Clair was testing a therapeutic oil for strong musculoskeletal pain, using St John's wort combined with other herbs.
St John's lesser-known properties were relieving nerve pain, nerve damage, sciatica, disc damage, shingles, burns, wounds and skin problems.
Mainstream painkillers, although very effective, often caused long-term side-effects.
While some knowledge had survived into modern times, many recipes had been forgotten, lost or destroyed.
Ms Clair was initially bemused when she translated that St John's was useful for female "silliness", assuming the author was being patronising or sexist. However, she discovered the early high German term related to menstrual pain.
"You get surprises like that all the time."
She was using a Materia Medica's recipe using angelica, which was famed in the Middle Ages for helping users ward off the black plague.
The book was the most comprehensive of its kind ever compiled, detailing 3000 plants, she said.
"This is it ... this is the pinnacle of herbal medical textbooks."
Previously, those with a "pet interest" in a herb had translated parts of it, but as far as she knew, hers was the first methodical translation.
"I've got to make sure that my methodology is correct and once I'm certain ... then I can open the research up not just for myself, but also for other researchers to come in." She was interested in how honey was used medicinally.
"[What] we have forgotten today and it makes complete sense to me ... is that they used to use honey together with herbal teas."
A particular strain of honey was prescribed to work in tandem with a herb, she said.
