Educational information, not medical advice — ask your doctor or midwife.
Yellow water lily is a pond plant of northern Europe. It has flat floating leaves and round yellow flowers. In Finland it is called ulpukka.
The part used in folk practice was the rhizome. That is the thick stem that creeps through the mud. Dried and ground, it was once stretched into famine bread.
Here is the short verdict. No human trial supports any health use of this plant. Long folk use is not proof that it works, and it is not proof that it is safe.
The root holds alkaloids that slow the heart and breathing in animal tests. For that reason this page gives no dose, no recipe and no course length.
Almost everything known about this plant comes from the lab, not from people.
The root contains a group of compounds called Nuphar alkaloids. In animal studies these appear to slow the heart and lower blood pressure. At higher amounts some also appear to slow breathing.
In test tubes, several of these alkaloids kill bacteria, fungi and tumour cells. That tells you nothing about what happens in a person who swallows the root.
Folk users valued the bitter taste and the slimy, starchy root. Bitter plants were thought to settle the gut. Slimy ones were thought to coat sore skin and sore throats.
Neither of those old ideas has been tested in a proper trial. So the honest answer is that we do not know how, or whether, it works in people.
There is no mainstream, tested product made from this plant.
What turns up is limited to:
Dried rhizome sold by foraging and wild-craft suppliers.
Home-made root tinctures and teas.
Seeds, named in old accounts as a wild starch food.
Powdered root, rarely, in niche herbal blends.
None of these are checked for alkaloid strength. Two batches from the same pond can differ.
This page does not describe how to prepare any of them. Given the heart-active alkaloids, a preparation method would read as an invitation to try it.
Nordic country people knew this plant first as food of last resort. In hungry years the rhizome was washed, leached and dried into a coarse flour.
Folk healers also put root washes and poultices on skin sores, boils and swellings. Some accounts list it for loose bowels and for heavy periods. It was also said to cool sexual desire, an idea shared with wider European water lily lore.
These records run from the 1700s through folk medicine collections of the 1800s and early 1900s. They describe what people once did. They are not a reason to repeat it.
Some reactions to Yellow water lily need urgent care. Call your local emergency number or go to an emergency department straight away — do not wait to see whether it passes.
Get emergency help at once if someone has swallowed this plant and shows any of these signs:
A slow, weak or irregular pulse.
Fainting, collapse or deep drowsiness.
Slow, shallow or laboured breathing.
Repeated vomiting, or vomiting with confusion.
Call your local emergency number or a poison centre. Take a piece of the plant or the product label with you.
See your doctor promptly for milder signs too, such as stomach cramps, dizziness or a rash after handling the root.
It is not approved as a medicine in the EU, the UK or the United States. Dried root is sometimes sold as a wild botanical or craft item, with no health claim allowed.
Do not swap one plant for another on your own. Each of these is a conversation to have with your doctor or pharmacist first.
For loose bowels: oral rehydration salts, which have strong human evidence.
For skin sores and boils: a proper wound dressing from a pharmacist, and a doctor's review if the area is hot, spreading or painful.
For heavy periods: ask your doctor about tranexamic acid or hormonal options, and about testing for low iron.
If you want a plant-based option, ask a pharmacist which products are approved in your country. Approved products carry a known strength; this root does not.
Evidence grades and traditional-use labels are explained in our methodology. Nothing here is medical advice.
What it is typically used for, usual dose, cautions, and the study behind it where real trial data exists.
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