Educational information, not medical advice — ask your doctor or midwife.
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Canada fleabane is a tall, weedy roadside plant used as a folk remedy for diarrhoea and for bleeding. Its botanical name is Erigeron canadensis, also written Conyza canadensis. Most people know it as horseweed.
The whole flowering plant is dried and used. A strong-smelling oil is also steam-distilled from it. Older American books call that oil "oil of erigeron".
Here is the honest verdict. There are no good human trials of this plant for any health use. Long folk use is not proof that it works, and it is not proof that it is safe.
Most of what we know comes from lab work on the plant's chemistry. That tells us what is in it. It does not tell us what it does in a person.
No one has shown how Canada fleabane works in people, because the human studies have not been done.
The main folk idea was astringency. The plant holds tannins, which bind to proteins in test-tube work. Healers thought this "tightened" an irritated gut and slowed loose stools.
That idea is plausible but unproven. Tannins do bind proteins in a glass dish. Whether a cup of the tea firms up stool in a person has not been tested.
The second idea came from the oil. The volatile oil irritates tissue, and older writers thought it stirred the kidneys to pass more water. This was never measured in a proper trial.
Lab studies on extracts of the plant report antioxidant and anti-bacterial activity in test tubes. Some animal work suggests effects on swelling and on blood sugar. These are early signals in animals and dishes, not results in people.
You may meet Canada fleabane in a few forms.
Dried herb, loose or in tea bags, for a hot infusion.
Liquid tincture, made with alcohol, sold in dropper bottles.
Fluid extract, a stronger liquid used by older herbalists.
Essential oil, steam-distilled from the plant. This is a concentrated product and is not for swallowing.
Capsules of powdered herb, which are less common.
The herb is sold by specialist suppliers rather than mainstream shops. Products are rarely standardised, so two bottles may differ in strength.
Canada fleabane sits in American folk and Eclectic practice, mainly in the 1800s and early 1900s.
Eclectic doctors listed it for diarrhoea and dysentery. They also gave it for bleeding, including heavy periods and bleeding from the gut or lungs. The oil was a favourite for this purpose.
It was also used as a diuretic (something that makes you pass more urine). Folk users gave it for gout, for joint pain and for bladder irritation.
The common name points to another old use. Dried bunches were burned or scattered to drive off fleas and gnats.
The plant is native to North America and spread widely across Europe and Asia. These uses are recorded history, not tested results.
Stop and get urgent help if you have swelling of the lips, face or tongue, a spreading rash, or trouble breathing. These are signs of a serious allergic reaction.
See a doctor the same day if you have bleeding you cannot explain, heavy bleeding, or blood in your stool or urine.
See a doctor if diarrhoea lasts more than two days, or sooner if you have a fever, severe pain, or signs of dehydration such as dizziness and dark urine.
Stop taking it and speak to a pharmacist or doctor if you feel sick, get a rash, or feel unwell in any way after starting it.
In the United States it is sold as a dietary supplement. It is not approved as a medicine there.
In the UK and the EU it has no traditional herbal registration and is not a licensed medicine. Sellers may not make treatment claims.
Evidence grades and traditional-use labels are explained in our methodology. Nothing here is medical advice.
Reviewed by the HealisticMD editorial team How we grade evidence →
The published evidence for Canada Fleabane is weak or absent. That usually means no controlled trial has tested it, not that a trial found it ineffective — the two are different, and we grade only what has been published.
What it is typically used for, usual dose, cautions, and the study behind it where real trial data exists.
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