Side Effects of Grapefruit Seed Extract

Grapefruit is high in vitamin C, soluble fiber, and antioxidants which makes it a good addition to any diet. A 2006 study in the "Journal of Agricultural and Food Chemistry" found that grapefruit can help lower blood triglyceride levels, especially in patients suffering from coronary artery disease. As a dietary supplement, it is available as grapefruit seed extract in pill, liquid or powder form. You should always consult your doctor before you take any supplement.

Effect on Enzymes

Grapefruit can inhibit the activity of certain liver and small intestine enzymes, reports a 1996 study in the journal, "Drug Metabolism and Disposition." Enzymes are catalysts that cause reactions to occur. In this case, the effect is on the digestive system. By inhibiting this enzymatic activity, concentrations of medications which rely on this mechanism for digestion can reach higher concentrations in the blood. According to Drugs.com, adverse reactions may result if you are taking calcium channel blockers or estrogen. The reduction of enzymatic activity can lead to elevated concentrations of these drugs in your blood.

Muscle Weakness

The Effects of Grapefruit on Synthroid

Learn More

Because grapefruit seed extract affects liver function, the risk for interactions with prescription drugs that also interact with the liver can be increased by taking this herbal supplement. Statin drugs are prescribed to lower blood cholesterol levels, but also have the potential to cause liver damage. The decrease in enzyme function can increase the concentration of these drugs. A rare side effect of statin drugs is a muscle weakening disease called Rhabdomyolysis. Because grapefruit seed extract alters statin metabolism, the possibility exists that you may be more at risk of developing this condition, according to a 2003 study in the "Journal of the American Medical Association."

Decreased Absorption of Medications

Grapefruit seed extract can also impair your body's ability to absorb medications, thereby decreasing their effectiveness. Fexofenadine is a non-sedating antihistamine prescribed for seasonal allergies. Grapefruit seed extract can inhibit your body's absorption of this drug by your system. It can also affect the absorption of other drugs including itraconazole, an antifungal, antibiotic and quinidine. Quinidine is an anti-malaria drug. However, it also is used for treating irregular heartbeat patterns. Grapefruit seed extract can potentially have very serious side effects on your cardiovascular system. Do not take grapefruit seed extract if you are on prescription medications without discussing possible drug interactions with your doctor.