Riddle argued that the ancient world possessed effective and safe contraceptives and abortifacients; however this knowledge about fertility control, widely held in the ancient world, was gradually lost over the course of the Middle Ages, becoming nearly unavailable by the early modern period. The reasons for this, Riddle argued, was that this knowledge was passed down through the oral and folk tradition, mainly by midwives, and belonged to a distinctly female-centered culture, removed from the male dominated and orientated knowledge of professionally trained physicians.

"All too often ancient herbal and other remedies have been dismissed as ’simply’ folklore, of no relevance to medical science. John Riddle’s approach, however, has been to explore the history of drugs with the hypothesis that ancient and medieval medicines were effective - a methodology that he expounds in the final essay (hitherto unpublished). Indeed, he shows, both from detailed case-studies and from the comparison of the listings given by classical and medieval authorities with those in modern pharmacopoeias, that our ancestors had discovered and made effective use of many of the drugs used in medicine today, from antiseptics and analgesics to oral contraceptives, even chemotherapy for cancer. There is the suggestion, therefore, that more careful examination and identification of the drugs used in the past may reveal chemicals that can be exploited anew. Central to these studies is the investigation of how a drug was used and how knowledge about it was transmitted - and perhaps also distorted in the process - from the Classical world through the Middle Ages" (publisher).

A history of the use of plant products, such as ergot, as abortion agents.