Dangers of Bilberry

A Spoonful of Bilberries with Bowl in Background

You may wonder, if bilberry is from Mother Nature and her plants are good for us, how might nature's balm for so many ailments also be dangerous? The dangers of bilberry are few; however, with all herbal preparations, there are specific risks to know of.

What Are the Dangers of Bilberry?

According to the National Center for Complementary and Integrative Health (NCCIH), bilberry, a plant bearing dark berries closely related to blueberries, is considered a safe herb to ingest in amounts typically found in foods for brief periods of time. It's also considered safe to use bilberry extracts short-term. The long-term effects of bilberry are not well-studied.

Research about bilberry and its potential dangers or side effects is limited. Much of what is known is based on research about bilberry's distantly-related family of fruit-bearing shrubs, such as cranberries, blueberries, and huckleberries.

Bilberry is a safe herbal remedy when taken in moderation. It is not a foodstuff like some of the other superfoods, such as chlorella and spirulina, where larger doses are thought harmless. The berries are edible, yet the plant is still a medicinal herb. Most of the known risks and side effects linked to bilberry involve long-term use of bilberry leaf, or using bilberry with other medicinal formulations.

Risks of Poisoning

Bilberry is a plant with medicinal effects; thus, poisonous interaction is always possible. Potential poisoning risks are linked to high doses of bilberry usage. These include tannin and chromium poisoning. There are no sufficient cases of poisoning reported.


The tannins within bilberry are useful for relieving digestive orders. However, according to Dr. Andrew Weil's website, tannins may be dangerous if taken in high dosages. Adverse symptoms include weight loss, tremors, or even death.


According to Drugs.com, taking bilberry while also taking chromium supplements, or foodstuff high in chromium, may lead to chromium poisoning. Foodstuff and herbs rich in chromium include:

  • Brewer's yeast
  • Cascara
  • Gentian Root
  • Horsetail
  • Wild Yam
  • Chromium supplements

Bilberry Leaves

Bilberry leaves are harvested to make tea. Although the leaves have many of the same chemical compounds found in the berry, PennState Hershey cautions that taking bilberry leaf or extract in large quantities over a long period may cause serious side effects including muscle spasm, major weight loss, or death. It's believed these may occur because of the leaf's high tannin levels. In addition, WebMD indicates bilberry leaf may lower blood sugar levels and should be used with caution under a doctor's supervision if you have diabetes or take diabetes medication.

Interactions With Drugs and Herbs

Bilberry may interact with certain medications, including herbal medications.

Anticoagulant Drugs

According to UMM, bilberry is one of nature's anticoagulants, thinning the blood and reducing blood clots due to its flavonoids known as anthocyanosides. If you use anticoagulant drugs, or take NSAID's such as Advil, consult with a qualified health care provider about taking oral doses of bilberry. Your health care provider may lower the medication doses, or depending on your medical history, discontinue the use of bilberry altogether. Moreover, discontinue bilberry two weeks before surgery. Below are several medications that may interact with bilberry:

  • Aspirin
  • Advil
  • Aleve
  • Anaprox
  • Cataflam
  • Dalteparin
  • Diclofenac
  • Enoxaparin
  • Etodolac
  • Heparin
  • Ibuprofen
  • Ketoprofen
  • Motrin
  • Naprelan
  • Naprosyn
  • Nuprin
  • Plavix
  • Warfarin

The following herbs are natural blood thinners with known cases of adverse interactions with bilberry:

  • Garlic
  • Ginkgo biloba
  • Saw palmetto

Anti-Diabetic Medications and Herbs

According to Prescription for Nutritional Healing: The A to Z Guide to Supplements by Phyllis A. Bach, glucoquinine is a natural compound found in bilberry, which is believed to reduce blood sugar levels. Glucoquinine may interact adversely with prescription drugs designed to lower blood sugar by inducing hypoglycemia, a condition of low blood sugar levels. A similar effect is noted in using bilberry with other herbal formulations known to decrease high blood sugar levels. Always consult with your medical practitioner before using bilberry with any of the following diabetes medications:

  • Avandia
  • Actos
  • Amaryl
  • DiaBeta
  • Diabinese
  • Glucotrol
  • Insulin
  • Micronase
  • Orinase

The following herbs are natural blood sugar regulators that may interact with bilberry:

  • Aloe Vera
  • Burdock
  • Devil's claw
  • Fenugreek
  • Garlic
  • Ginseng
  • Ginger
  • Guar gum
  • Horse chestnut
  • Milk Thistle
  • Psyllium
  • Stinging Nettle

What Is the Recommended Dosage?

If you are thinking of starting bilberry supplements and are generally healthy, WebMD recommends a daily dosage between 20 to 160 mg. Consume doses from the lower end of the spectrum in good health (20 to 60 mg daily), and take up to 160 mg when treating preexisting conditions. Two daily doses of 160 mg are sometimes prescribed to treat retinal diseases and cataracts. Do not go beyond 160 mg a day unless an herbalist or qualified health provider gives specific instructions otherwise.

Bilberry leaf tea is made by steeping one to two teaspoons finely chopped bilberry leaf in 150 ml (a little over 1/2 a cup) boiling water. Strain before drinking. Only use bilberry leaf for a short period.

Are There Any Other Risks?

Before using bilberry, there are additional risks to be aware of.


Mixing different bilberry preparations together may increase the risk of overdose. As a precaution, stick to one form of bilberry at a time unless otherwise directed. Bilberry preparations include tea, supplements, extracts, or tinctures. Just the same, there are no reports of overdose linked to bilberry.

Allergic Reactions

While allergic reactions to bilberry are rare, they may still occur as with any plant. If you are allergic to the Ericaceae family of plants, or to anthocyanosides, you may wish to err on the side of caution and avoid bilberry. The Mayo Clinic lists the following as potential allergic reaction symptoms:

  • Anxiety
  • Confusion
  • Rash
  • Hives
  • Diarrhea
  • Nausea
  • Vomiting
  • Closing of the throat
  • Difficulty breathing
  • Swelling of the skin
  • Swelling of the lips, tongue or face

If you, or someone you know, experience the following symptoms, seek medical attention immediately.

A Tasty Traditional Remedy in Moderation

Bilberry has been used for centuries as food and medicine. This relative of the blueberry is delicious in jams, jellies, and pies. But don't let its sweet taste fool you. Although bilberry is considered a safe herbal remedy when used short-term, using it is not without risk. Talk to your doctor or a natural health practitioner to determine if bilberry is right for you.

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Dangers of Bilberry