A Storm of Chemistry

Moon tea offers the women of the Seven Kingdoms and beyond The Wall some control* over their lives – a rarity in a series. This herbal tea is a birth control method, implied – or explicitly stated – to be an abortifacient. In George R.R. Martin’s The Storm of Swords, a recipe for moon tea is given by Lady Lysa as “…tansy and mint and wormwood, a spoon of honey and a drop of pennyroyal.”

Moon tea is fiction, but three of its ingredients have long histories in birth control – tansy, wormwood, and pennyroyal plants. While the use of herbal abortifacients goes back far beyond a millennium, their effectiveness and safety is as inconsistent as the weather of WesterosASOIAF aficionado Butterfly wrote in 2013 “…moon tea is ~fantasy~, but don’t try it at home.” As Butterfly notes, our three historical plants are toxic. Why are these three plants toxic? It comes down to the chemicals pugelone and thujone. En route to these compounds are moon tea’s honey and mint.

Asoiaf.westor.org member Eden-Mackenzie pointed out, “[m]int and honey can be eliminated as the dangerous ingredients, and are likely included to help with taste and/or smell.”  Butterfly’s moon tea post says honey and mint are safe. I would agree with safety assessment for honey and one of the two mints in Martin’s moon tea recipe. This fictional tea contains two members of the Menta genus – Mentha spicata and Mentha pulegium. By tradition, only Mentha spicata – commonly known as spearmint – gets the official nickname ‘mint‘. Mentha pulegium**  is better known by its common name of pennyroyal.

Mentha genus members share many common properties and produce a lot of the same chemicals. Pennyroyal, along spearmint and peppermint, all produce R-(+)-pulegone, a chemical known simply as ‘pulegone’.

R-(+)-pulegone (image from chemspider)
R-(+)-pulegone (image from chemspider)
Pulegone is colorless oil and a hepatotoxic (liver damaging) monoterpene. ‘Monoterpene’ defines the chemical’s structure – a shorthand likely known only to chemists and biochemists. This monoterpene is found in an array of Mentha members, but it’s present in pennyroyal at a higher level. Pulegone is present in pennyroyal oil at a stratospherically higher level compared to other popular Mentha oils. Pennyroyal oil is  ~85-97% pugelone. Peppermint and spearmint oils are ~4% and ~2% pulegone, respectively. As Eden-Mackenzie argued, the use of “a drop” for this plant – compared to the other plants listed – implies the use pennyroyal oil and not a drop of tea. Pennyroyal oil is highly toxic because of its pulegone level.  The National Institute of Health (NIH) Toxicology Data Network has this to say about pulegone:

…patients may present within 2 hours of ingestion with nausea, vomiting, abdominal pain, burning of the throat, and dizziness before the delayed development of liver dysfunction. Significant pennyroyal oil ingestions can lead to fulminant hepatic failure, acute renal failure, disseminated intravascular coagulation, metabolic acidosis, gastrointestinal bleeding, pulmonary congestion, altered mental status, seizures, and death.

What constitutes a “significant” amount of pennyroyal oil? From the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK):
Pennyroyal oil, however, is highly toxic, and even small does (one tablespoon, 15 mL) can cause syncope, seizures, coma, cardiopulmonary collapse, acute liver injury, renal insufficiency and multiorgan failure.
[emphasis added]

You can see why Martin’s recipe calls for only a drop of pennyroyal oil.  Pennyroyal tea and leaf extracts, with their minty scent, has been used historically to flavor foods and beverages “…without serious side effects,” according to the NIDDK.  It boils down to a higher dose of pulegone being required to see the “serious side effects” mentioned above. What about the abortive effect? Pregnancy termination  “…may occur with marked maternal toxicity or death,” according to the NIH’s Toxicology Data Network.  At the levels of pugelone that may end a pregnancy, come multi-organ and multi-system damage. The history of pennyroyal as an abortifacient is marked with serious maternal injury and death, with poor efficacy as an abortifacient, as detailed Kaye Wierzbicki’sA Cup of Pennyroyal Tea‘ at The Toast. While a drop of pennyroyal might be safer, lower risk likely means no abortive effect.

Joining pennyroyal in this awful realm of dangerous, unpredictable herbal abortifacients are tansy and wormwood. Both tansy and wormwood are in Asteraceae plant family, diverging at the genus level. These two plants – Tanacetum vulgare L. (tansy) and Artemisia absinthium L. (wormwood) – share a common feature. Both produce alpha-thujone and beta-thujone, two isomers collectively called ‘thujone’.

Structures from chemspider (alpha and beta)
Structures from chemspider (alpha and beta)

Thujone, like pugelone, is classified a monoterpene. It smells like menthol (minty) and is a colorless oily-like liquid. Thujone is often classified as a neurotoxin based on its dose-dependent action on the central nervous system, with the most noted effect being epileptiform convulsions. Like pennyroyal, a cup of tansy or wormwood tea probably doesn’t contain enough thujone to bring about “serious side effects”. Tansy and wormwood oils would contain significantly more thujone and acute oil poisonings could result in the following:

…vomiting, gastroenteritis, flushing, cramps, loss of consciousness, rapid breathing, cardiac arrhythmia, enteric bleeding and hepatitis. Death occurs from circulatory or respiratory arrest and degenerative organ changes…
Though our pair of thujones are often lumped together, alpha-thujone is more potent and induces effects at much lower concentrations than beta-thujone. Tansy oil has ~15-35 times more alpha-thujone than wormwood oil, but beta-thujone dominates in both oils. If the oils were used, different volumes of each would be required and Martin’s recipe doesn’t provide a dispensing volume guide as it did for pennyroyal. Even if the oil volumes were provided, the pennyroyal problem would pop up again. That is, the dose required would be likely bring “maternal toxicity or death”. As stated in the 1920 Annual Report on Essential Oils, Synthetic Perfumes, &c, “[a]bortion in these cases is to be looked upon as a secondary effect of the general and severe damage done to the health.”

It doesn’t seem as if Martin’s moon tea recipe calls for the oils of tansy or wormwood. There’s no talk of drops, just herb names. This implies the use of leaves, either dried or fresh. In the real world, a cup of moon tea may^ not be enough to terminate a pregnancy, with the accompanying damage to maternal health. Like real herbal concoctions women have turned to throughout history, a few cups a day for a week would likely be consumed in pursuit of pregnancy termination. Such chronic, rather than acute, exposure in no way guarantees termination or maternal safety. If this tea worked in the Seven Kingdoms as it would in real life, the women of ASOIAF would face with the same poor birth control^^ options real women have faced throughout history and into the modern day. Good thing moon tea exists in fantasy world.

Want more ASOIAF science? Check out the GoT blog carnival posts below! 

*This isn’t the case for Lady Lysa, but no spoilers here.

**This is European pennyroyal. American false pennyroyal, Hedeoma pulegioides L., also produces pulegone and its essential oil is ~30% pulegone.

^Dosage is key and this person’s size can determine the significance of a toxins impact.

^^Even in the fantasy world of ASOFAI, the choice to use moon tea can have terrifying consequences, but no spoilers here.


The featured image was created with clipart in PowerPoint.


DrRubidium is an analytical chemist that spends her days finding needles in needlestacks. Also a science communicator, she focuses on the the science behind everyday stuff and pop culture.

Related Articles


  1. I didn’t know pennyroyal was a mint, or an abortifacient, before today. I do know the smell though. As a child, I spent several summers in upstate Massachusetts at an old inn officially called ‘The Pennyroyal Arms.’ We knew it by the owner’s name: Spurr’s.

    Pennyroyal was widely used as an insect repellent, certainly as late as the 1930s and the inn’s name was a mocking reference to the six-legged wildlife that abounded in the Berkshires.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Back to top button