Drug-Nutrient Interactions and Drug-Supplement Interactions | Examples of Dietary Supplement Interactions

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Learn More About Drug-Nutrient Interactions and Drug-Supplement Interactions

Drug Interactions with St. John's Wort

Dietary supplements can affect the way your body processes prescription and over-the-counter drugs. When this happens, your medicine may not work the way it should. This is called a drug-supplement interaction. It can cause serious problems.

Supplement: Black Cohosh

Possible drug-supplement interaction with:

  • Medicines changed by the liver.* Some medicines are processed and broken down using the liver's cytochrome P450 enzyme system. Echinacea may decrease how quickly the liver breaks down these medicines, which can increase effects and side effects. Talk to your doctor to see if you are taking a medicine that is changed by the liver.

Supplement: Cranberry

Possible drug-supplement interaction with:

  • Warfarin. Cranberry may increase the amount of time warfarin is in the body. This increases the risk of bruising and bleeding.

Supplement: St. John’s Wort

Read here about interactions.

Supplement: Soy isoflavones

Possible drug-supplement interaction with:

  • Estrogen. Soy isoflavones may decrease the effectiveness of estrogen pills.
  • Tamoxifen. Can affect estrogen levels, decreasing effectiveness of tamoxifen.
  • Warfarin. Can increase the amount of time warfarin is in the body, increasing the risk of bruising and bleeding.

Supplement: Garlic

Possible drug-supplement interaction with:

  • Isoniazid. Can reduce amount of isoniazid body absorbs, decreasing effectiveness.
  • HIV/AIDS Medicines. Can increase how fast medicine is broken down, reducing effectiveness.
  • Saquinavir. Can increase how fast medicine is broken down, reducing effectiveness.

Supplement: Echinacea

Possible drug-supplement interaction with:

  • Caffeine. May decrease how quickly the body breaks down caffeine, causing jitteriness, headache and rapid heartbeat.
  • Medicines changed by the liver.* Some medicines are processed and broken down using the liver's cytochrome P450 enzyme system. Echinacea may decrease how quickly the liver breaks down these medicines, which can increase effects and side effects. Talk to your doctor to see if you are taking a medicine that is changed by the liver.
  • Immunosuppresants. May increase activity of the immune system, which can  decrease the effectiveness of the medicine.

Supplement: Ginseng

Possible drug-supplement interaction with:

  • Warfarin. May decrease the effectiveness of warfarin, which can increase the risk of blood clots.

Supplement: Ginkgo

Possible drug-supplement interaction with:

  • Alprazolam. May decrease the effects of alprazolam.
  • Efavirenz. May decrease effectiveness of efavirenz.
  • Ibuprofen. Slows blood clotting, which increases the chance of bruising and bleeding.
  • Medicines changed by the liver.*  Some medicines are processed and broken down using the liver's cytochrome P450 enzyme system. Ginkgo may decrease how quickly the liver breaks down these medicines, which can increase effects and side effects.  Talk to your doctor to see if you are taking a medicine that is changed by the liver.
  • Diabetes medicines. May affect insulin levels, which can decrease effectiveness of the medicines.
  • Anticonvulsants. May affect chemicals in the brain, which can decrease effectiveness of the anticonvulsants.
  • Trazodone. May affect chemicals in the brain, which can cause serious side effects in the brain.
  • Warfarin. May slow blood clotting in addition to the warfarin, which can increase chance of bruising and bleeding.

Supplement: Milk Thistle

Possible drug-supplement interaction with:

  • Medicines changed by the liver.* Some medicines are processed and broken down using the liver's cytochrome P450 enzyme system. Milk thistle may decrease how quickly the liver breaks down these medicines, which can increase the effects and side effects. Talk to your doctor to see if you are taking a medicine that is changed by the liver.
  • Glucuronidated medicines. Can decrease how well liver breaks down the medicines, which can increase or decrease its effectiveness.
  • Tamoxifen. Can increase how much tamoxifen is absorbed by the body.

Supplement: Saw Palmetto

Possible drug-supplement interaction with:

  • Birth control pills. Can decrease effects of estrogen in the body, which can reduce the effectiveness of birth control pills.
  • Estrogen. Can decrease estrogen levels in the body, which can decrease the effectiveness of estrogen pills.
  • Anticoagulant /Antiplatelet medicines. Can slow blood clotting, which can increase the risk of bruising and bleeding.

Supplement: Bilberry

Possible drug-supplement interaction with:

  • Diabetes medicines. Can decrease blood sugar, which can cause blood sugar to reach dangerously low levels.
  • Anticoagulant /Antiplatelet medicines. Can slow blood clotting, which can increase the risk of bruising and bleeding.

Supplement: Chaste Tree Berry

Possible drug-supplement interaction with:

  • Birth control pills. Can affect hormone levels, decreasing effectiveness.
  • Dopamine receptor antagonists. Can affect how the body breaks down the medicine.

Supplement: Devil's Claw

Possible drug-supplement interaction with:

  • Medicines changed by the liver.* Some medicines are processed and broken down using the liver's cytochrome P450 enzyme system. Devil’s claw may decrease how quickly the liver breaks down these medicines, which can increase the effects and side effects. Talk to your doctor to see if you are taking a medicine that is changed by the liver.
  • Warfarin. Can decrease the effectiveness of warfarin, increasing the risk of blood clots.

Supplement: Feverfew

Possible drug-supplement interaction with:

  • Medicines changed by the liver.* Some medicines are processed and broken down using the liver's cytochrome P450 enzyme system. Feverfew may decrease how quickly the liver breaks down these medicines, which can increase the effects and side effects. Talk to your doctor to see if you are taking a medicine that is changed by the liver.
  • Anticoagulant /Antiplatelet medicines. Can slow blood clotting, which can increase the risk of bruising and bleeding.

Supplement: Goldenseal Root

Possible drug-supplement interaction with:

  • Cyclosporine. Can decrease how fast the body breaks down cyclosporine, which can increase side effects.
  • Medicines changed by the liver.* Some medicines are processed and broken down using the liver's cytochrome P450 enzyme system. Goldenseal root may decrease how quickly the liver breaks down these medicines, which can increase the effects and side effects. Talk to your doctor to see if you are taking a medicine that is changed by the liver.
  • Medicines moved by pumps in cells (P-Glycoprotein Substrates). Can make pumps less active, increasing amount of medicine absorbed by the body.

Supplement: Licorice Root

Possible drug-supplement interaction with:

  • Diuretics, Corticosteriods. Can reduce potassium to dangerously low levels.
  • Prednisone. Can affect levels of cortisol in the body, affecting the medicine’s ability to work properly.

Supplement: Horse Chestnut

Possible drug-supplement interaction with:

  • Lithium. Can decrease how well body gets rid of lithium, which can cause serious side effects.
  • Diabetes medicines. Can decrease blood sugar, causing blood sugar to reach dangerously low levels.
  • Anticoagulant / Antiplatelet medicines. Can slow blood clotting, which can increase the risk of bruising and bleeding.

Supplement: Turmeric (curcurmin)

Possible drug-supplement interaction with:

  • Anticoagulant / Antiplatelet drugs. Can slow blood clotting, which can increase the risk of bruising and bleeding.

Supplement: Valerian

Possible drug-supplement interaction with:

  • Alcohol. Can cause drowsiness in addition to the alcohol, resulting in too much sleepiness.
  • Sedative medicines (benzodiazepines and CNS eepressants). Can cause drowsiness in addition to the effect of the sedative, resulting in too much sleepiness and prolonged sedation during surgery.

*Examples of medicines changed by the liver can include: amitriptyline, diazepam, zileuton, celecoxib, diclofenac, fluvastatin, glipizide, ibuprofen, irbesartan, losartan, phenytoin, piroxicam, tamoxifen, tolbutamide, torsemide, warfarin, lovastatin, ketoconazole, itraconazole, fexofenadine, triazolam, and many others.

Written by familydoctor.org editorial staff

Created: 02/14

Learn More About Drug-Nutrient Interactions and Drug-Supplement Interactions

Drug Interactions with St. John's Wort

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