Grape seed contains a rich store of oliogmeric proanthocyanidins, antioxidants with numerous potential health benefits. The French have used grapeseed extract for many years to address varicose veins and other circulatory disorders. Other potential uses include diabetes, atherosclerosis, heart conditions and cancer, but not enough evidence exists to draw any firm conclusions about its benefits. Many supplements have been made from muscadine grapes, in particular. They do not appear to pose any special risks compared to other types of supplements but grape seed extract in general does have some potentially adverse effects associated with it. Generally, however, it seems a safe supplement. If you believe taking grape seed will address a particular health concern, talk to your doctor first.
Drugs.com notes reports of allergic reactions to grape seed documented in scientific literature. The National Center for Complementary and Alternative Medicine states grape seed might cause side effects such as nausea, indigestion, increased blood pressure, itchy scalp, dizziness, headache and hives.
Interactions between medications and this supplement have not been closely examined, according to NCCAM. Certain actions of grape seed, however, suggest potential interactions to keep in mind. It can potentially thin the blood, which could increase the effectiveness of anticoagulant medications like warfarin. These medications require highly individualized doses and using any treatment that could affect their actions even slightly might require dosage adjustments. Do not combine these two treatments without talking to your doctor.
The Memorial Sloan Kettering Cancer Center reports grape seed might interfere with the actions of the enzymes P450 3A4 and UGT, which means using it at the same time as medications that require these enzymes for breakdown could lead to negative effects like reduced effectiveness of the drug or an increased risk of side effects. A large number of drugs require these enzymes. If you take any sort of medication, talk to your doctor about possible interactions with grape seed.
Considerations for Certain Individuals
The Beth Israel Deaconess Medical Center reports using grape seed extract and vitamin C supplements at the same time might increase blood pressure in hypertensive individuals but that either supplement in isolation does not appear to cause this issue. The University of Maryland Medical Center recommends checking with your doctor before using grape seed if you have a bleeding disorder due to its potential blood –thinning effects. If you have liver or kidney disease or are pregnant or nursing, always clear the use of supplements with your doctor.
Other Safety Concerns
The University of Maryland Medical Center reports that using grape seed extract at the recommended doses appears safe for up to three months. The effects of longer-term use have not been established. The doses vary depending on the condition but typically consist of 150 to 300 mg daily, though Drugs.com notes some studies used up to 900 mg. Your doctor can suggest the appropriate dose as well as how long you can safely use it.