Educational information, not medical advice — ask your doctor or midwife.
Small cranberry is the wild bog cranberry of northern Europe, Vaccinium oxycoccos. It is a low, creeping evergreen shrub with thin stems and tiny leaves. The berries are red, sour and picked from peat bogs in autumn.
In the Nordic countries it is known as tranebær, tranbär and karpalo. People eat it as juice, jam and sauce. Capsules of cranberry extract are also sold as supplements.
The honest verdict: cranberry products may modestly lower the chance of repeat urinary tract infections in some women and children. Almost all of that research used the American cranberry, a close relative. Long traditional use does not prove a remedy works, and it does not prove it is safe.
If you take antiplatelet medicines (drugs that stop blood cells clumping together), read the safety notes below first.
The leading idea is that cranberry makes it harder for bacteria to stick to the bladder wall.
In laboratory studies, plant compounds called A-type proanthocyanidins appear to stop E coli bacteria gripping bladder cells. Bacteria that cannot grip are more likely to be washed out in urine. This has been seen mainly in cell and test-tube work.
An older idea was that cranberry makes urine acidic and so kills bacteria. Human studies do not support this well. The acid change in urine is small and short-lived.
Is the anti-sticking effect strong enough in real bladders? That is still debated. Trials that measured bacteria in urine often found no clear drop.
In short, the trial results are better supported than the explanation for them.
Common forms include:
- Fresh or frozen berries - Juice, often sweetened or blended with apple - Jam, sauce and dried sweetened berries - Capsules or tablets of dried extract - Powder for drinks
Strength varies a lot between products. Juice drinks may hold only a small share of real cranberry. Extract capsules are often labelled by their proanthocyanidin content, which lets you compare them.
Sweetened juice and dried berries can carry a lot of sugar. Unsweetened juice is very sour and is usually diluted.
Small cranberry was a staple wild food across Scandinavia, Finland and northern Russia. Bogs were harvested in late autumn, and berries were also picked after the first frost or in spring.
The berries keep well. A common household method was storing them in cold water, where their own acids held spoilage back through winter. That made them a winter source of fresh fruit in a hard climate.
Folk use included drinks for fever, gargles for sore mouths and throats, and preparations for bladder and kidney complaints. Sailors and northern households valued sour berries against the illness we now call scurvy. These are records of what people did, not advice to copy.
See a doctor promptly if you have burning when you pass urine, need to go very often, or see blood in your urine.
Get urgent care for fever, chills, vomiting, or pain in your back or side. These can mean a kidney infection.
Also seek care for sharp one-sided back pain that comes in waves, which may be a kidney stone. Stop cranberry and call your doctor if you notice easy bruising or unusual bleeding while on warfarin.
In the EU, Norway and the UK, cranberry berries and juice are ordinary foods. Extracts are sold as food supplements, not as medicines. EU regulators have not approved a health claim linking cranberry to urinary tract health, so products may not promise it.
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.
