# Epsom salt

**Sal catharticum*; bitter salt*

**Known today as.** Magnesium sulfate, first boiled from the waters of a spring on Epsom Common in Surrey.

Kind: Mineral

## What was it used for?

A purge, sold across Europe from the 1690s; bathed in, and drunk at the wells.

## What does modern science say?

Still a laxative. Given into a vein, magnesium sulfate prevents seizures in eclampsia of pregnancy, and it is used in severe asthma.

## Pharmacognosy and toxicology

- **magnesium sulfate**: 

**Mechanism.** By mouth the salt holds water in the bowel; into a vein, magnesium blocks calcium channels and NMDA receptors and stops the seizures of eclampsia, where the Collaborative Eclampsia Trial (1995) showed it beat diazepam and phenytoin and the Magpie trial (2002) showed it beat placebo.

**Dose.** Magnesium poisoning from enemas and from laxative abuse in kidney failure: weakness, a slowed heart, and stopped breathing.

**Standing.** On the WHO list of essential medicines for pre-eclampsia and eclampsia.

## What lore surrounds it?

The story goes that in 1618 a farmer named Henry Wicker found his cows refusing the bitter water of a spring on the common, though they were thirsty; the water became famous for its purging.

## What did the older authorities say?

**Nehemiah Grew.** Obtained the salt from the water and took out a patent for making it in 1698.

## Sources

- Grew, N. (1695). *Tractatus de salis cathartici amari in aquis Ebeshamensibus*.
- Altman, D., et al. (2002). “Do women with pre-eclampsia, and their babies, benefit from magnesium sulphate? The Magpie Trial.” *Lancet* 359.

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*Epsom salt.* In *Materia Medica*, edited by B. C. P. Statema. Version 1, revised 2026-09-30. The Thinking Press. https://thethinkingpress.org/materia-medica/epsom-salt

Historical description, not medical advice.