Bilberry (Vaccinium myrtillus) : Safety and Interactions

by MedlinePlus

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Safety

The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.

Allergies

People with allergies to plants in the Ericaceae family or to anthocyanosides may have reactions to bilberry. However, there are no reliable published cases of serious allergic reactions to bilberry.

Side Effects and Warnings

Bilberry is generally believed to be safe in recommended doses for short periods of time, based on its history as a foodstuff. There are no known reports of serious toxicity or side effects, although if taken in large doses, there is an increased risk of bleeding, upset stomach, or hydroquinone poisoning.

Based on human use, bilberry fresh fruit may cause diarrhea or have a laxative effect. Based on animal studies, bilberry may cause low blood sugar levels. Caution is therefore advised in patients with diabetes or hypoglycemia, and in those taking drugs, herbs, or supplements that affect blood sugar. Serum glucose levels may need to be monitored by a healthcare provider, and medication adjustments may be necessary. In theory, bilberry may decrease blood pressure, based on laboratory studies. With the use of bilberry leaf extract, there is a theoretical increased bleeding risk, although there are no reliable published human reports of bleeding.Caution is advised in patients with bleeding disorders, taking drugs that may increase the risk of bleeding, or prior to some surgeries and dental procedures.

Pregnancy and Breastfeeding

There is not enough scientific evidence to recommend the safe use of bilberry in pregnancy or breastfeeding, although eating bilberry fruit is believed to be safe based on its history of use as a foodstuff. One study used bilberry extract to treat pregnancy-induced leg swelling (edema), and no adverse effects were reported.

Interactions

Most herbs and supplements have not been thoroughly tested for interactions with other herbs, supplements, drugs, or foods. The interactions listed below are based on reports in scientific publications, laboratory experiments, or traditional use. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy.

Interactions with Drugs

Based on animal research, bilberry may lower blood sugar levels. There are no reliable human studies in this area. Caution is advised when using medications that may also lower blood sugar. Patients taking drugs for diabetes by mouth or insulin should be monitored closely by a qualified healthcare provider. Medication adjustments may be necessary.

Based on human use, bilberry may increase diarrhea when taken with drugs that cause or worsen diarrhea, such as laxatives or some antibiotics. Bilberry theoretically may increase the risk of bleeding when taken with drugs that increase the risk of bleeding. Some examples include aspirin, anticoagulants ("blood thinners") such as warfarin (Coumadin®) or heparin, anti-platelet drugs such as clopidogrel (Plavixv), and non-steroidal anti-inflammatory drugs such as ibuprofen (Motrin®, Advil®) or naproxen (Naprosyn®, Aleve®). There are no reliable published human reports of bleeding with the use of bilberry. Based on theory, bilberry may further lower blood pressure when taken with drugs that decrease blood pressure.

Based on early laboratory study, berry extracts have been shown to inhibit H. pylori, an ulcer producing bacteria and enhance the effects of the prescription drug clarithromycin (Biaxin ®).

Interactions with Herbs and Dietary Supplements

Based on animal research, bilberry may lower blood sugar levels. Although there is no reliable human study in this area, caution is advised when using herbs or supplements that may also lower blood sugar. Blood glucose levels may require monitoring, and doses may need adjustment. Possible examples include Aloe vera , American ginseng, bitter melon, burdock,fenugreek, fish oil, gymnema, horse chestnut seed extract (HCSE), marshmallow, milk thistle, Panax ginseng, rosemary, Siberian ginseng, stinging nettle and white horehound.

Based on theory, bilberry may further lower blood pressure when taken with herbs or supplements that decrease blood pressure. Herbs that potentially may have this effect include aconite/monkshood, arnica, baneberry, betel nut, black cohosh, bryony, calendula, California poppy, coleus, curcumin, eucalyptol, eucalyptus oil, ginger, goldenseal, green hellebore, hawthorn, Indian tobacco, jaborandi, mistletoe, night blooming cereus, oleander, pasque flower, periwinkle, pleurisy root, shepherd's purse, Texas milkweed, turmeric, and wild cherry.

Based on theory, bilberry may increase the risk of bleeding when taken with herbs and supplements that are believed to increase the risk of bleeding. Multiple cases of bleeding have been reported with the use of Ginkgo biloba , fewer cases with garlic, and two cases with saw palmetto. Numerous other agents may theoretically increase the risk of bleeding, although this has not been proven in most cases. Some examples include: alfalfa, American ginseng, angelica, anise, Arnica montana , asafetida, aspen bark, birch, black cohosh, bladderwrack, bogbean, boldo, borage seed oil, bromelain, capsicum, cat's claw, celery, chamomile, chaparral, clove, coleus, cordyceps, danshen, devil's claw, dong quai, evening primrose, fenugreek, feverfew, flaxseed/flax powder (not a concern with flaxseed oil), ginger, grapefruit juice, grapeseed, green tea, guggul, gymnestra, horse chestnut, horseradish, licorice root, lovage root, male fern, meadowsweet, nordihydroguairetic acid (NDGA), onion, papain, Panax ginseng, parsley, passionflower, poplar, prickly Ash, propolis, quassia, red clover, reishi, Siberian ginseng, sweet clover, rue, sweet birch, sweet clover, turmeric , vitamin E, white willow, wild carrot, wild lettuce, willow, wintergreen, and yucca.

Based on traditional use, bilberry may increase diarrhea or laxative effects when taken with herbs and supplements that are also believed to have laxative effects. Possible herbs with this property include alder buckthorn, aloe dried leaf sap, black root, blue flag rhizome, butternut bark, dong quai, European buckthorn, eyebright, cascara bark, castor oil, chasteberry, colocynth fruit pulp, dandelion, gamboges bark, horsetail, jalap root, manna bark, plantain leaf, podophyllum root, psyllium, rhubarb, senna, wild cucumber fruit, and yellow dock root.

Consuming bilberry with quercetin supplements may result in additive effects, based on one small study in which bilberry consumption resulted in higher serum concentrations of quercetin. Cooking bilberries with water and sugar to make soup may decrease the amount of quercetin by 40%. Berries contain resveratrol which has been studied as an antioxidant, for cardiovascular disease and cancer and may have additive effects when taken with supplements like grapeseed.

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