Educational information, not medical advice — ask your doctor or midwife.
Glasswort, sold as marsh samphire, is a small green salt-marsh plant with fleshy, jointed stems. It grows on tidal mud along European coasts. People eat the young stems as a salty vegetable.
Most of its use today is culinary. Cooks serve it steamed, blanched or raw beside fish. It is also sold dried, as a powder, in capsules, and as a "green salt" made from the whole plant.
Here is the honest verdict. Glasswort is a nutritious vegetable that is very high in salt. Good human evidence that it treats any illness is thin, and long folk use is not proof that something works or that it is safe.
Most of what glasswort does in the body comes from its minerals and fibre, not from a drug-like action.
The plant soaks up sea salt as it grows. So eating it adds sodium, plus some potassium, magnesium and iodine. That salt load is the main reason it can affect blood pressure and fluid balance, usually by raising them rather than lowering them.
In test tubes and in animals, Salicornia extracts have shown effects on blood fats, blood sugar and markers of swelling and irritation. Those findings come from the lab bench, not from people. Whether any of it happens in a human body is not established.
Some makers sell glasswort salt as a lower-sodium seasoning, because part of its mineral content is potassium rather than sodium. That swap is plausible on paper. It has not been shown in good trials to improve health outcomes.
You will meet glasswort in a few forms:
- Fresh stems, sold in fish markets and greengrocers in late spring and summer - Pickled or brined stems in jars - Dried, milled powder sold loose or in capsules - "Green salt" or vegetable salt made from the dried plant - Extracts used in skin creams and cosmetics
Fresh samphire is a food and is treated as one. The powders, capsules and salts are the forms sold with health claims attached.
Foraged glasswort is a special case. It is legal to pick in some places and protected in others, and marsh pollution is a real risk.
European coastal communities ate glasswort for centuries as a free spring green. It was pickled for winter and sold cheaply in port towns.
Its name comes from industry, not medicine. Burning the plant gave soda ash, which was used to make glass and soap. German Queller and French salicorne refer to the same plant.
Folk writers also recorded it as a water pill (diuretic), as a remedy for worms, and as a green eaten to ward off scurvy on the coast. These were household customs of their time. They are recorded here as history, not as advice to try.
Stop using glasswort powders, capsules or plant salt and speak to a doctor or pharmacist if you notice any of these:
- Ankles, fingers or face that swell up - Sudden weight gain over a few days - Breathlessness, especially when lying flat - A clear rise in your home blood pressure readings - Constant thirst or a big change in how much you pass urine - Headache with a pounding heartbeat
Seek urgent care for chest pain, severe breathlessness, or swelling of the lips, tongue or throat.
Tell your doctor you have been using it if you take lithium, heart or kidney medicines.
In the UK and the EU, glasswort is an ordinary food vegetable and is sold freely as produce, powder or seasoning. It is not licensed as a medicine, so health claims on packs are restricted. Picking wild plants may be limited on protected salt marshes and nature reserves.
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.
One email with the summary. We'll also send a short weekly evidence update — unsubscribe any time.
