Herb Interactions With Medications

Chemotherapy drugs (metabolism interactions)

• Quercetin can affect the activity of cytochrome P450 enzymes in the liver, which are responsible for metabolizing many chemotherapy drugs.

• This means it could raise or lower drug levels in the bloodstream, potentially reducing treatment effectiveness or increasing toxicity.

P-glycoprotein and drug transporters

• Quercetin has been shown to inhibit P-glycoprotein, a protein that pumps drugs out of cells.

• On one hand, this might make chemotherapy drugs more effective against resistant cancer cells.

• On the other, it may increase toxicity, since the body’s normal clearance mechanisms are disrupted.

Specific drugs where caution is noted in studies

• Cisplatin – Quercetin may reduce its kidney toxicity in some animal studies, but it could also alter how cisplatin is processed in the body.

• Doxorubicin – Quercetin can increase the uptake of this drug into cells, which might enhance anticancer activity but also raise the risk of side effects.

• Paclitaxel and Vincristine – Quercetin can interfere with metabolism and drug transport, affecting their activity.

Blood thinners (e.g., warfarin)

• Quercetin has mild blood-thinning effects and may increase bleeding risk when combined with anticoagulants.

Corticosteroids

• Some evidence suggests quercetin can affect steroid metabolism, potentially changing how drugs like dexamethasone work.

Chemotherapy drugs

• Licorice compounds can affect drug metabolism in the liver (via cytochrome P450 enzymes). This may alter the blood levels of certain chemotherapy medications, either reducing their effectiveness or increasing toxicity.

Corticosteroids (e.g., prednisone, dexamethasone)

• Licorice prolongs the activity of corticosteroids by slowing their breakdown. This can lead to enhanced steroid effects and side effects, such as immune suppression, fluid retention, and elevated blood pressure.

Blood pressure and heart medications

• Licorice may cause sodium retention and potassium loss, raising blood pressure and increasing the risk of heart rhythm problems—important for cancer patients already at risk of cardiovascular side effects from treatment.

Blood thinners (e.g., warfarin)

• Licorice can reduce the effectiveness of warfarin, increasing the risk of clotting. This is especially concerning for cancer patients with higher clot risk.

Diuretics

• When combined with diuretics, licorice can intensify potassium loss, which may trigger muscle weakness, cramping, or dangerous heart rhythm disturbances.