# Blackthorn (Prunus spinosa)

*Sloe*

**Known today as.** *Prunus spinosa*. A thorny hedgerow shrub bearing small, bitter, blue-black plums, sloes, after the first frost.

Kind: Plant  
Poisoning: Cyanide from the kernels (https://thethinkingpress.org/materia-medica/poisons/cyanogenic)

## What was it used for?

Sloes made into wine, syrup, and sloe gin; the bark and flowers used as an astringent and a mild laxative in the older herbals.

## What does modern science say?

The fruit is a genuine source of tannins and vitamin C once cooked or frosted; raw sloes are too astringent to eat.

## Pharmacognosy and toxicology

- **amygdalin**: in the kernel; a cyanogenic glycoside
- **proanthocyanidins**: in the fruit and bark
- **quercetin and kaempferol glycosides**: in the flower

**Mechanism.** The flower is a mild laxative and diuretic by its flavonoids; the fruit is astringent by its tannins; the kernels, like all *Prunus* kernels, release cyanide when crushed and eaten.

**Dose.** The fruit and flower are safe; kernels in quantity are not, and a handful of bitter kernels has poisoned children in the related species.

**Standing.** The flower is in the German tradition (Commission E, 1990) for mild constipation; no clinical trials.

## What lore surrounds it?

Blackthorn was called the witches’ own tree in the British Isles, its wood cut for wands and staffs and its thickets said to shelter fairies; Thomas Weir of Edinburgh, the “Wizard of West Bow,” was said to carry a blackthorn staff carved with a satyr’s head, given him by the Devil. Irish tradition made its timber into the shillelagh, and English country sayings call a sudden cold snap during its early blossom a “blackthorn winter,” while “many sloes, many groans” and “many sloes, many cold toes” read a heavy crop as the omen of a hard winter.

## What did the older authorities say?

**Culpeper.** “It is so well known, that it needs no description.” The fruit “ripens after all other plums whatsoever, and is not fit to be eaten until the Autumn frost mellow them.” “All the parts of the Sloe-Bush are binding, cooling, and dry, and all effectual to stay bleeding at the nose and mouth, or any other place; the lask of the belly or stomach, or the bloody flux.” The distilled water of the flowers, “first steeped in sack for a night,” is “a most certain remedy, tried and approved, to ease all manner of gnawings in the stomach, the sides and bowels,” and the leaves make lotions “to gargle and wash the mouth and throat.”

## Sources

- Royal Botanic Garden Edinburgh, “The Blackthorn Tree of British and Irish Folklore.”
- Culpeper, N. (1653). *The Complete Herbal*, “The Black Thorn, Or Sloe-Bush.” Project Gutenberg #49513.
- Blumenthal, M., ed. (1998). *The Complete German Commission E Monographs*, “Blackthorn flower.”
- Bolarinwa, I. F., et al. (2014). “Amygdalin content of seeds, kernels and food products commercially available in the UK.” *Food Chemistry* 152.

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*Blackthorn.* In *Materia Medica*, edited by B. C. P. Statema. Version 1, revised 2026-10-01. The Thinking Press. https://thethinkingpress.org/materia-medica/blackthorn

Historical description, not medical advice.