Anticoagulants (blood-thinning medication) -- In theory, because the anthocyanosides in bilberry may stop blood from clotting, there may be an increased risk of bleeding if you take bilberry with blood-thinning medication, including aspirin. The whole fruit may be safer in these instances. Ask your doctor before taking bilberry if you take blood-thinning medication.

Medication for diabetes -- Because bilberry appears to lower blood sugar, it could make the effects of diabetes medication stronger. Also, taking bilberry with other herbs that also lower blood sugar may result in hypoglycemia (low blood sugar). Herbs that also lower blood sugar include ginger, ginseng, fenugreek, and garlic. Do not take bilberry if you take medications for diabetes.