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Commonly sold under the trade-name Pycnogenol®, pine bark extract is an herbal antioxidant supplement derived from the French maritime pine tree (Pinus maritima). Advocates of pine bark extract suggest that this compound and similar related compounds have protective effects against many disorders, including arthritis, diabetes, cancer and heart disease. Although scientific research, to a limited extent, supports many of these claims, few of the studies have utilized clinical trials, and fewer have focused on potential safety issues of this compound.

Common Transient Side Effects

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As reported by the American Cancer Society, most reported pine bark extract side effects are mild and transient. Similar reported side effects are commonly associated with many dietary supplements. These include nausea, headache and upset stomach. However, since the safety of pine bark extract is not fully investigated in humans, any adverse reaction, mild or otherwise, could potentially be a sign of bigger underlying issues and should not be ignored. Consult your doctor.

Immune System Side Effects

Pine bark extract has poorly understood effects on the immune system, however, several reports have indicated possible immunosuppressant properties of this compound. For example, in a 2003 article in "Phytotherapy Research," researchers report the finding that in rats, pine bark extract can inhibit histamine release, an important regulator of the allergic response. For this reason, pine bark extract may be contraindicated in people with a weakened immune system. Pine bark extract may exacerbate the effects of immunosuppressant drugs, such as those prescribed for organ transplant recipients. Pine bark extract may also interfere with medication used to boost immune function.

Blood Pressure and Bloodstream Side Effects

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According to a 1999 article in "Free Radical Biology and Medicine," pine bark extract inhibits the activity of angiotensin-converting enzyme, or ACE, an essential enzyme in the regulation of hypertension. For this reason, according to the MedlinePlus website, pine bark extract can potentially interact with blood pressure-lowering medications, particularly with ACE-inhibitors such as enalapril and captopril. Pine bark extract may also increase the risk of bleeding, which could worsen effects of blood thinners such as ibuprofen or warfarin.

Cancer Drug Interactions

While there is no direct evidence that pine bark extract will interact with cancer chemotherapeutic drugs, it is important to note that antioxidants are often contraindicated with such medicine. As suggested by the Cancer Supportive Survivorship Care website, the same protective effects that antioxidants have against damaging reactive oxygen species in normal tissue also can often inhibit the toxic effects of chemotherapy drugs.

Other Potential Adverse Reactions

Pine bark extract may decrease blood sugar levels and should be used cautiously in patients suffering from hypoglycemia or diabetes, according to Medline Plus. It is also possible that you could have an allergic reaction to pine bark extract, which could range from mild to potentially life-threatening complications.