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The Pope Who Advocated Birth Control

Pope John XXI prescribed an herbal forerunner of the pill.

Original cartoon by Alex Martin
Source: Original cartoon by Alex Martin

Oftentimes, topics originally discussed in my 2013 book How We Do It: The Evolution and Future of Human Reproduction and revisited in this blog resulted from serendipity—making fortunate discoveries by accident. A prime example, providing the theme for this blog piece, is the presence in certain plants of organic substances that mimic steroid hormones and impact reproduction. In 2007, a paper by James Higham and colleagues—including Ann MacLarnon and Caroline Ross, two of my former Ph.D. students—reported intriguing findings from a long-term field study of wild baboons in Nigeria. At times when the baboons ate fruits and young leaves of a particular tree species, menstrual cycles were suppressed and no females conceived. This report spurred me to find out whether any related species exert comparable effects on humans. In an unexpected and roundabout fashion, I then stumbled on the fascinating story of an early Pope who provided tips for herbal birth control.

A tree that affects monkey reproduction

To underpin observations of the natural behavior of two baboon troops, Higham and colleagues collected their droppings for hormone analyses. Back in the laboratory, they discovered that all females showed marked seasonal spikes in organic compounds that closely resembled the steroid hormone progesterone. Progesterone plays a key part in reproduction in all mammals, supporting pregnancy and suppressing ovulation. In a prime example of scientific detective work, Higham and colleagues sifted through over a thousand hours of field records. They eventually discovered that the spikes in progesterone-like compounds (progestins) occurred only when both baboon troops were feeding on fruits and young leaves of the African black plum (Vitex doniana). Laboratory tests confirmed that high progestin levels are indeed present in samples from this tree. Remarkably, during periods of feeding on black plum, progestin surges in the droppings of female baboons far exceeded the very high levels excreted during pregnancy.

 Adapted version of a figure in Higham et al. (2007).
Left: Plains baboon (Papio anubis) feeding on ground-living plants. Right: Graph showing spikes in fecal progestins (PdG) at times when one troop Nigerian baboons fed on fruits and young leaves of Vitex doniana. Similar results were found with a second troop.
Source: Left: Image from Wikimedia Commons. Author: guiguibu91 (2007); file licensed under the Creative Commons Attribution 2.0 Generic license. Right: Adapted version of a figure in Higham et al. (2007).

Further examination revealed that the unusually high progestin levels found in baboons when feeding on black plum trees affected their reproductive biology. Most obviously, the progestins suppressed sexual swelling, marked inflation and reddening of the female genital region that indicates cyclical changes in the ovary. Combined analyses of birth records and hormonal profiles showed that no female baboons conceived during peak periods of feeding on black plum. So natural consumption of fruits and leaves of this tree seemingly suppresses processes in the ovary and exerts a contraceptive effect. In short, it mimics pregnancy in the same way as the human Birth Control Pill. Blocking of sexual swelling by progestins from black plum trees was accompanied by a decline in the frequency with which female baboons formed close associations (consortships) with individual males and a decreased occurrence of mating.

Adapted version of two figures in Higham et al. (2008).
Changing height of sex swellings in female Nigerian baboons across the menstrual cycle. Day 0 = Ovulation time inferred from fecal hormone levels.
Source: Adapted version of two figures in Higham et al. (2008).

Chimpanzees at the renowned Gombe field site in Tanzania are known to feed on a tree related to the African plum, the Meru oak (Vitex fischeri). The apes consume fruits of this species during a short annual fruiting season lasting little more than a month. A 2008 paper by Melissa Emery Thompson and colleagues reported that urine samples collected over the course of one 5-week fruiting season revealed dramatically increased progestin levels in females at this time, far above normal values. Although no female chimpanzees conceived during the period of feeding on Vitex fischeri, however, the authors were unable to test for any long-term effects on reproduction.

Keeping monks chaste

I soon discovered that the flora of Europe’s Mediterranean region includes a shrub belonging to the same genus as the African plum tree, bearing the scientific name Vitex agnus-castus. Tellingly, two common names for this plant are chasteberry and monk's pepper. Moreover, the formal species name agnus-castus is a needless conjunction of Greek and Latin words both indicating “chaste”. Like the African black plum, chasteberry produces progestins. As one reflection of this, mediaeval monks reportedly drank chasteberry potions to help them keep their vows of celibacy.

 O. Penzig). File from the Biodiversity Heritage Library, licensed under the Creative Commons Attribution 2.0 Generic license.
Chasteberry plant (Vitex agnus-castus) from France. The species occurs on the banks of fast-moving streams and on coastal dunes in the Mediterranean region.
Source: Figure from Wikimedia Commons. Source: Flore Coloriée de Poche du Littoral Méditerranéen de Gênes à Barcelone y Compris la Corse (author: O. Penzig). File from the Biodiversity Heritage Library, licensed under the Creative Commons Attribution 2.0 Generic license.

In fact, chasteberry has been used as a herbal medicine for over two millennia—dating back to ancient Egypt and Greece—mainly to treat gynaecological ailments. One prominent application has been stimulation of menstruation (a once common code name for inducing abortion), and modern clinical studies have identified benefits for treating menstrual disorders and infertility. In his 1992 book, Contraception and Abortion from the Ancient World to the Renaissance, American medical historian John Riddle cited evidence that chasteberry has long been used for contraception as well. Pedanius Dioscorides, the leading First Century authority on ancient medicines, stated in his treatise De Materia Medica (On Medical Materials), written between AD 50 and 70, that chasteberry "destroys generation as well as provokes menstruation". Overall, it seems that small quantities of chasteberry can stimulate menstruation, whereas high doses may block conception or induce abortion.

The physician who became Pope

So now to the early Pope who provided tips for herbal birth control. Following Pope Gregory X’s demise in January 1276, three successive popes had to be elected in the course of a single year. Both Innocent V and Adrian V were elected and died before the year was out, and Pope John XXI (confusingly also known as “Peter of Spain“) was their successor.

John XXI is notably the only Pope with medical training. Born as Pedro Julião in Portugal in around 1215, he began his studies at the episcopal school of Lisbon Cathedral. After that, he moved to France, where he studied medicine, theology, logic, physics, metaphysics and Aristotle's dialectic. He then taught medicine at the University of Siena, Italy, where he wrote Summulae Logicales, a treatise on Aristotelian logic that served as an academic reference work in Europe for more than three centuries. Eventually, he became Gregory X’s personal physician before being elected Pope in his turn in 1276.

 Illustration from Wellcome Images, a website operated by Wellcome Trust. File licensed under the Creative Commons Attribution 4.0 International license.
Left: Portrait of Pope John XXI (1215-1277). Right: Title page of “Thesaurus Pauperum” (expanded version published in 1530).
Source: Images from Wikimedia Commons. Left: Faithful photographic reproduction of a two-dimensional work of art in the public domain. Right: Illustration from Wellcome Images, a website operated by Wellcome Trust. File licensed under the Creative Commons Attribution 4.0 International license.

At some stage, Pope John XXI compiled a hugely popular practical medical guide entitled Thesaurus Pauperum (Treasure of the Poor). That text is a readily understandable compendium of prescriptions dealing mainly with mundane concerns such as warts. But Thesaurus Pauperum also provided practical advice not only on coitus and arousing or taming sexual desire but also on birth control. Various concoctions to be swallowed in that context included chasteberry.

Tragically, John XXI occupied his post for only eight months. He insisted on continuing his scientific studies even after his election and had an extension built onto the papal palace at Viterbo for that purpose. One day in May 1277, while he was working alone in this annexe, the ceiling collapsed, and his injuries proved to be so severe that he succumbed six days later. He was buried in the Duomo di Viterbo, where his tomb can still be visited. One can only imagine what this perceptive and dedicated physician might have achieved if that fatal accident had not happened. Eight centuries ago, John XXI’s medical compendium came remarkably close to recommending an equivalent of the modern contraceptive pill, and that may well be his most striking legacy.


Ambrose, C.T. (2013) Medicus Petrus Hispanus (ca. 1205-77 Peter of Spain): a XIII century pope and author of a medieval sex guide. Journal of Medical Biography 21:85-94.

Berger, D., Schaffner, W., Schrader, E., Meier, B. & Brattström, A. (2000) Efficacy of Vitex agnus castus L. extract Ze 440 in patients with pre-menstrual syndrome (PMS). Archives of Gynecology & Obstetrics 264:150-153.

Emery Thompson, M., Wilson, M.L., Gobbo, G., Muller, M.N. & Pusey, A.E. (2008) Hyperprogesteronemia in response to Vitex fischeri consumption in wild chimpanzees (Pan troglodytes schweinfurthii). American Journal of Primatology 70:1064-1071.

Higham, J.P., MacLarnon, A.M., Ross, C., Heistermann, M. & Semple, S. (2008) Baboon sexual swellings: Information content of size and color. Hormones & Behavior 53:452-462.

Higham, J.P., Ross, C., Warren, Y., Heistermann, M. & MacLarnon, A.M. (2007) Reduced reproductive function in wild baboons (Papio hamadryas anubis) related to natural consumption of the African black plum (Vitex doniana). Hormones & Behavior 52:384-390.

Loch, E.-G., Selle, H. & Boblitz, N. (2000) Treatment of premenstrual syndrome with a phytopharmaceutical formulation containing Vitex agnus castus. Journal of Women’s Health & Gender-Based Medicine 9:315-320.

Martin, R.D. (2013) How We Do It: The Evolution and Future of Human Reproduction. New York: Basic Books.

Riddle, J.M. (1992) Contraception and Abortion from the Ancient World to the Renaissance. Cambridge, MA: Harvard University Press.

Schellenberg, R. (2001) Treatment for the premenstrual syndrome with agnus castus fruit extract: prospective, randomised, placebo controlled study. British Medical Journal 322:134-137.

Zimmerman, M. (2013) Pope promotes birth control. HuffPost.