What is Blackthorn?

Blackthorn is a thorny hedgerow shrub found across Europe. Its small blue-black fruits are called sloes. In German-speaking folk use it is known as Schlehe.

The white spring flowers were brewed as a light tea. The ripe sloes were turned into syrup, jam, gargles and sloe gin. Raw sloes are sharp and leave the mouth dry and puckered.

Today it is sold as a food and as a mild herbal tea. It is not a treatment for any disease.

Here is the honest verdict. Human evidence for blackthorn as a medicine is close to absent. Long traditional use is not proof that it works, and it is not proof that it is safe.

How does Blackthorn work?

No one has shown what blackthorn does in the human body. The ideas below come from the lab, not from patients.

The fruit is rich in tannins. Tannins bind proteins and make tissue feel tight and dry.

That is why a sloe gargle was thought to soothe a raw throat. This is a chemical effect you can taste, not a proven treatment.

In test-tube work, sloe extracts show antioxidant activity. Some lab studies report that they slow the growth of certain bacteria in a dish. Whether any of this happens inside a person is not known.

The flower tea was used as a gentle laxative and a "water tea". The flowers hold flavonoids and small amounts of other plant acids. No trial has tested whether the tea moves the bowels better than warm water.

One mechanism is real, and it is a hazard rather than a benefit. The seed inside the sloe stone holds amygdalin, a cyanogenic glycoside (a plant compound that can give off cyanide).

When the seed is crushed and eaten, the body can release cyanide from it. This is well established for seeds across the Prunus family, which also includes plums, cherries and apricots.

What forms does Blackthorn come in?

You will meet blackthorn far more often as a food than as a remedy.

Common forms: - Dried flowers, loose or in herbal tea bags - Sloe syrup, juice and jam - Sloe gin and other fruit liqueurs - Dried fruit powder in blends - Tinctures and fluid extracts - Homeopathic preparations, which contain little or no plant material

Strength varies a lot between products. Picking season, ripeness and drying all change what ends up in the cup.

Where it comes from:

Blackthorn has a long and well-recorded place in European folk practice.

The flowers were gathered in early spring. They were brewed as part of a "spring cure", meant to clear the body after winter. Folk writers also called the tea a mild laxative and a gentle water tea.

The fruit was picked after the first frosts, which softened its bite. Country households made sloe syrup and sloe wine. A sloe gargle was a common home measure for a sore mouth or throat.

German and Austrian herbal books carried blackthorn flower for centuries. That record shows steady use over time. It does not show that the plant helped.

The shrub also had a folk life beyond medicine. Hedges of blackthorn kept livestock in and strangers out. Its wood was cut into walking sticks and clubs.

What does Blackthorn help with?

• Mild, occasional constipation: This is the best-known folk claim for the flower tea. European herbals listed it as a very gentle laxative. There are no human trials behind it. Any effect may simply be the warm fluid. If your bowels have changed for more than a few weeks, see a doctor.
• Sore throat and sore mouth, as a gargle: Tradition used sloe syrup or a fruit gargle for a raw throat. The tannins make tissue feel tighter and drier, which you can taste at once. That is not the same as healing an infection. No trial has tested a sloe gargle in people.
• Mild short-term diarrhoea: Astringent fruits were used this way across Europe. Tannin-rich plants do bind and dry tissue in the lab. Human evidence for sloes is missing. Do not treat diarrhoea with blood, black stools or high fever at home.
• Spring tonic and general wellbeing: Flower tea was drunk as a seasonal cure after winter. This is a cultural habit, not a medical claim. "Tonic" has no measured meaning. There is nothing to test and nothing has been shown.
• Mild fluid retention: Folk sources called the flower tea a water tea, meaning it made people pass more urine. No study has measured this. Swollen legs or ankles can signal heart, kidney or liver trouble. That needs a doctor, not a tea.

Which foods are rich in Blackthorn?

Sloes are eaten as food in Europe, mostly after the first frost softens them. They turn up in jam, syrup, fruit wine and sloe gin. Food amounts of the ripe flesh are not a safety worry for most healthy adults.

What are the side effects of Blackthorn?

• Upset stomach or belly cramps
• Loose stools, if you drink a lot of the flower tea
• Dry, puckered feeling in the mouth
• Nausea from very sour unripe fruit
• Allergic reaction, such as rash, itching or swelling
• Possible lower iron uptake from a meal, from the tannins
• Cyanide poisoning if crushed seeds are eaten

Good to know:

The ripe fruit is an ordinary food and is well tolerated by most people. Mild stomach upset is the usual complaint. Allergy is uncommon but possible, especially if you react to plums, cherries or almonds.

The serious risk sits in the seed, not the flesh. Crushed or chewed seeds can release cyanide. Swallowing a whole stone by accident is far less of a concern than deliberately crushing seeds.

How much Blackthorn should you take?

• Recommended daily: This page gives label-style amounts only, not advice for you. Herbal tea labels for dried sloe flower usually suggest about 1 to 2 grams per cup, once or twice a day. Sloe syrup labels often give a spoonful. Follow the product label. Ask a pharmacist if you take other medicines. There is no tested dose for any health effect. No amount has been shown to treat anything.
• Best time of day: Timing does not matter much. People who drink the flower tea for the bowels often take it in the evening, out of habit. A gargle is used when the throat feels sore.
• With or without food: Either is fine. Strong tannin teas can upset an empty stomach. Taking it with or after food may be easier.
• Time to effect: Be ready for nothing to happen. If a mild laxative effect comes at all, it would be within a day. A gargle feels drying in the mouth right away. That is a taste effect, not healing. No lasting benefit has been shown in people.
• How long to take it: Short use only, in the range of days to a week or two. No one has studied long-term use. Daily laxative teas can become a habit and can mask a real bowel problem. If you feel you need it every day, that is a reason to see a doctor.