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Cranberry
Cranberry — what the European monograph actually supports, what it is not for, the form and how long it is meant to be used, side effects, and the 2 medicine interactions documented for it.
This is a reference page, not a diagnosis and not a prescription. Herbal products are real pharmacology: they have effects, side effects and interactions with medicines. Tell your doctor and your pharmacist everything you take, including teas and supplements, and never stop or change a prescribed medicine because of anything you read here.
What it is
Vaccinium macrocarpon Aiton — fruit and juice
Local names across the region this site serves: jõhvikas (ET) · karpalo (FI) · клюква (RU).
Grouped here under Joints, urinary tract and hormones. Regulatory position: Food and food supplement; not a monographed herbal medicine for infection in the EU.
What the evidence supports
The registered indication: Reducing the chance of repeat urinary tract infections in some groups — not treating an infection that is already present.
Cranberry is the rare case where a large, independent systematic review moved the answer. A Cochrane review of cranberry products, updated in 2023, concluded that they reduce the risk of repeat symptomatic, culture-confirmed urinary tract infections in women with recurrent infections and in children, while finding no clear benefit in several other groups — older people in institutions, people with bladder-emptying problems, and pregnant women. The proposed mechanism is proanthocyanidin interference with bacterial adhesion to the bladder wall, and product strength varies enormously, which is why "cranberry" as a category performs less consistently than any single trial. A regional footnote: the Estonian jõhvikas and Finnish karpalo are the native small cranberry, Vaccinium oxycoccos; the fruit in supplements is almost always the larger American species.
B — Traditional use, trials point the same way Registered on long-standing use, and independent reviews of human trials point in the same direction without settling the question.
What it is not for
Treating an infection. Burning, urgency, fever, flank pain or blood in the urine need to be seen, because an untreated urinary infection can reach the kidneys. Cranberry does not replace antibiotics and does not shorten an infection.
Form, strength and how long
Capsules and tablets standardised to proanthocyanidin content, unsweetened juice, and sweetened juice drinks, which are mostly sugar and water.
Duration. Prevention is by definition long-term, which makes the sugar content of juice products a genuine consideration.
No gram figure appears on this page on purpose. The plant part, the extraction solvent and the drug-to-extract ratio together define a preparation, and a number taken from one does not describe another. The reasoning is set out on the hub; the amount that applies to you is the one printed on the pack you are holding, and a pharmacist will read it with you.
Side effects
Stomach upset and diarrhoea at high intakes. Cranberry is relatively high in oxalate, which is a consideration for people who form calcium-oxalate kidney stones.
Who should avoid it
Fine as a food for most people. Anyone with recurrent infections should still have the reason for them looked at rather than only prevented.
Interactions with medicines
| Medicine or substance | What is described |
|---|---|
| Anticoagulants and antiplatelets (warfarin, DOACs, aspirin, clopidogrel) | UK regulators issued a caution in the early 2000s after reports of raised INR in warfarin patients drinking cranberry juice. Later controlled studies have been largely reassuring, but the standing advice has not changed: keep intake steady and tell whoever monitors your INR. |
| Diabetes medicines and insulin | Sweetened cranberry juice drinks carry a substantial sugar load; unsweetened juice and capsules do not. |
The reverse view — start from the medicine rather than the plant — is in the medicine, food and alcohol interactions reference, and summarised for every herb on this site.
As a food
This one is also in the kitchen, so the nutrition figures are worth having next to the pharmacology: see the food data page for calories and nutrients per 100 g and per portion. Culinary amounts and medicinal preparations are different exposures, and the difference is usually the whole safety story.
Sources: NIH National Center for Complementary and Integrative Health — herb fact sheets · checked 2026-09-06
Frequently asked questions
What is cranberry used for?
Reducing the chance of repeat urinary tract infections in some groups — not treating an infection that is already present. Cranberry is the rare case where a large, independent systematic review moved the answer. A Cochrane review of cranberry products, updated in 2023, concluded that they reduce the risk of repeat symptomatic, culture-confirmed urinary tract infections in women with recurrent infections and in children, while finding no clear benefit in several other groups — older people in institutions, people with bladder-emptying problems, and pregnant women. The proposed mechanism is proanthocyanidin interference with bacterial adhesion to the bladder wall, and product strength varies enormously, which is why "cranberry" as a category performs less consistently than any single trial. A regional footnote: the Estonian jõhvikas and Finnish karpalo are the native small cranberry, Vaccinium oxycoccos; the fruit in supplements is almost always the larger American species.
Does cranberry work?
Graded B here: Registered on long-standing use, and independent reviews of human trials point in the same direction without settling the question. Treating an infection. Burning, urgency, fever, flank pain or blood in the urine need to be seen, because an untreated urinary infection can reach the kidneys. Cranberry does not replace antibiotics and does not shorten an infection.
How much cranberry should I take?
This reference does not print gram figures, because they do not transfer between preparations of different extract strength. What can be said honestly is the form and the duration: Capsules and tablets standardised to proanthocyanidin content, unsweetened juice, and sweetened juice drinks, which are mostly sugar and water. Prevention is by definition long-term, which makes the sugar content of juice products a genuine consideration.
What are the side effects of cranberry?
Stomach upset and diarrhoea at high intakes. Cranberry is relatively high in oxalate, which is a consideration for people who form calcium-oxalate kidney stones.
Does cranberry interact with medicines?
Yes — documented for Anticoagulants, warfarin, Diabetes medicines. Each one is described on this page, with a link to the medicine-side reference where one exists.
Others in joints, urinary tract and hormones
Nettle
Leaf: to increase the amount of urine and so flush the urinary tract in minor complaints, and for minor joint pain. Root: lower urinary tract symptoms related to benign enlargement of the prostate.
Saw palmetto
Relief of lower urinary tract symptoms related to benign prostatic hyperplasia, after a doctor has excluded serious conditions.
Black cohosh
Relief of menopausal complaints such as hot flushes and profuse sweating.
Devil's claw
Relief of minor joint pain, and of mild digestive complaints such as bloating and loss of appetite.
Feverfew
Prophylaxis of migraine headaches, after serious conditions have been excluded by a doctor.
Keep the whole list in one place
TempoLife logs supplements alongside food, sleep and how you actually felt — so the answer to "what are you taking?" is a screen, not a guess.