Licorice may interfere with certain drugs

Extract led to more or less absorption in rats, depending on the drug

SALT LAKE CITY — Licorice has long been used as a good treatment for plenty of ills, but the compound that gives the extract its healing powers may also interfere with certain drugs, suggests new research in rats. The findings, presented March 24 at a meeting of the American Chemical Society, suggest that some patients should hold off from sweets made with the plant extract.

Studies in rats suggest that licorice may block the effectiveness of some drugs, including cyclosporine, a drug widely used by transplant patients. American Chemical Society

Glycyrrhizin, the active compound in licorice, is a major constituent found in the roots of Glycyrrhiza species, a group of plants in the pea family. The extract has a long history of medicinal use in Europe and Asia, and as a flavoring for sweets (though some licorice candies, including Good & Plentys, are flavored with a combination of licorice and anise, an extract from an unrelated plant, or anise alone). In Asia, “It’s used more as a drug, not as a candy,” says Pei-Dawn Lee Chao of the China Medical University in Taichung, Taiwan.

Scientists are also exploring how glycyrrhizin, heralded for its bioactive properties, interacts with therapeutic drugs. Led by Chao, researchers fed rats cyclosporine, a drug that suppresses the body’s immune response and is often taken by transplant patients. The team also gave the rats various concentrations of pure glycyrrhizin and licorice extract. The researchers found that levels of cyclosporine in the rats’ blood dropped considerably in rats fed licorice or pure glycyrrhizin.

Chao speculates that the glycyrrhizin may kick the protein known as P-glycoprotein, or Pgp, into gear. Pgp has been shown to mediate the path of some drugs from the blood to the bile or urine. But the licorice extract appears to operate via several mechanisms, cautions Chao. Her group found that glycyrrhizin has the opposite effect in rats fed the drug methotrexate, an immune suppressing drug that’s given to chemotherapy patients. Levels of methotrexate increased and stayed high in the blood of the rats, suggesting the drug wasn’t being absorbed, the team reported online February 11 in the Journal of Agricultural and Food Chemistry. So patients should consult their doctors about potential drug interactions, Chao says.

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