Can Herbs Interact With Medications? 18 Herbal Supplements

1. St. John’s wort (Hypericum perforatum)

St. John’s wort is widely used as a safe alternative to conventional antidepressant drugs for mild to moderate forms of depressive disorders.

This herb can speed up the process of changing the drug into inactive substances, leading to a decrease in drug levels in the body. It can interact with many types of drugs and can cause harmful side effects, including:

• Immunosuppressants (cyclosporine, tacrolimus, and prednisone)
• Hormones (oral pill, tibolone)
• Cardiovascular drugs (warfarin, phenprocoumon, digoxin, simvastatin, rosuvastatin, and atorvastatin)
• Calcium blockers (nifedipine and verapamil)
• β1-adrenoreceptor blockers (talinolol)
• Antianginal drugs (ivabradine)
• Antiretroviral drugs (indinavir, nevirapine)
• Anticancer drugs (irinotecan, imatinib)
• Drugs acting on the central nervous system (alprazolam, midazolam, quazepam, and buspirone)
• Antidepressants (paroxetine, venlafaxine, sertraline, nefazodone, and amitriptyline)
• Antiepileptic drugs (methadone, bupropion, chlorzoxazone, and dextromethorphan)
• Antiulcer medications (omeprazole)
• Antidiarrheal drugs (loperamide)
• Drugs acting on the respiratory system (theophylline and fexofenadine)
• Antifungal drugs (voriconazole)
• Antimigraine drugs (eletriptan)

2. Concentrated garlic extracts (Allium sativum)

Garlic extract is used in modern phytotherapy to treat hypercholesterolemia and prevent arteriosclerosis.

It can lead to thinning of the blood (similar to aspirin), which may cause complications (excessive bleeding) during or after surgery.

3. Ginger (Zingiber officinale)

Ginger preparations effectively reduce nausea and vomiting during pregnancy and after surgery.

Though not confirmed by clinical trials, preclinical studies have shown that ginger supplements may lead to an elevated international normalized ratio when taken concomitantly with the anticoagulant phenprocoumon.

4. Ginkgo (Ginkgo biloba)

Extracts from the leaves of the ginkgo tree are used for the treatment of cognitive impairments, dementia, intermittent claudication, and tinnitus.

Recent controlled clinical data have suggested that ginkgo extracts could cause spontaneous hyphema with aspirin, intracerebral hemorrhage with warfarin, and intracerebral mass bleeding with ibuprofen.

5. Ginseng (Korean ginseng, panax ginseng)

Ginseng is believed to promote health and longevity, restore male sexual function, and aid in healing and recovery.

Some case reports suggest that there may be potentially serious interactions when ginseng is used with the antidepressant phenelzine and the anticancer drug imatinib.

6. Ginseng (American ginseng)

A clinical trial found that American ginseng has the potential to reduce the anticoagulant effect of warfarin.

7. Concentrated green tea (Camellia sinensis)

Green tea is a beverage that is also used as an herbal drug.

Green tea supplements can interact with pseudoephedrine (a decongestant) and may reduce the anticoagulant effect of warfarin.

8. Aloe vera

Aloe vera is often used as a laxative (contains anthraquinones) and for skin conditions (contains mucilage).

There has been speculation about the interaction between aloe vera and the anesthetic sevoflurane. Both sevoflurane and aloe vera ingredients may inhibit platelet aggregation.

9. Kava (Piper methysticum)

Kava roots and rhizomes are used to treat anxiety. It contains kavalactones, which are powerful inhibitors of several cytochrome P450 (CYP) enzymes.

10. Black cohosh (Cimicifuga racemosa)

The rhizome and roots of this plant are primarily used to treat symptoms of menopause and have been associated with serious safety concerns, such as hepatotoxicity.

11. Cat’s claw (Uncaria tomentosa)

Cat’s claw is used for conditions such as rheumatoid arthritis and AIDS.

In-vitro (test-tube) studies report that it can increase the plasma concentration of the protease inhibitors atazanavir, ritonavir, and saquinavir. However, this has not been confirmed in humans.

12. Milk thistle (Silybum marianum)

Milk thistle is mostly used to treat liver diseases.

It may have minor effects on the pharmacokinetics of drugs metabolized by CYP enzymes or transported by P-glycoprotein.

13. Red yeast rice

Red yeast rice is made by fermenting cooked rice using the fungus Monascus purpureus and is used to lower blood cholesterol.

It is believed to cause rhabdomyolysis when used in combination with cyclosporine treatment.

14. Ephedra (ma huang)

Ephedra is commonly found in herbal weight loss products, commonly referred to as herbal fen-phen.

The use of this product is speculated to interact with caffeine, decongestants, and stimulants.

15. Chamomile (Matric aria recutita)

Fresh or dried flower heads of chamomile are used topically for skin and mucous membrane inflammation and internally to treat gastrointestinal spasms and inflammatory diseases of the gastrointestinal tract.

It contains coumarins that may exert an anticoagulant effect, which may work synergistically or additively with warfarin, resulting in over-anticoagulation.

16. Goldenseal (Hydrastis canadensis)

Goldenseal is used to treat gastrointestinal disturbances, urinary disorders, skin ailments, and various infections.

Clinical evidence suggests that adverse herb-to-drug interactions may result from concomitant ingestion of goldenseal and drugs that are metabolized by CYP3A4 or CYP2D6.

17. Peppermint (Mentha piperita)

Peppermint leaf and oil have long been used to treat digestive disorders and symptoms of irritable bowel syndrome.

Some clinical studies suggest that peppermint might increase the levels of drugs metabolized by CYP3A4, such as felodipine.

18. Licorice (Glycyrrhiza glabra)

Licorice roots and rhizomes are used to treat peptic ulcers and catarrhs of the upper respiratory tract.

Researchers suggest that this herbal remedy should be used with caution when taken at the same time as other drugs that interact with CYP3A4.

According to the WHO, herbal medicines are defined as labeled medicinal products or plant preparations (juices, gums, fatty oils, or essential oils) that contain active ingredients, parts of plants or other plant material, or combinations of these:

• Herbal medicines may or may not contain excipients in addition to active ingredients.
• Unlike conventional drugs, herbal products are not tested with scientific rigor, and they are not even subjected to the FDA approval process.
• Herb-to-drug interactions are based on the same principles as drug-to-drug interactions: pharmacokinetic (changes in plasma drug concentration) and pharmacodynamic (drugs interacting at receptors on target organs).
• Some adverse effects and drug interactions reported for herbal products could be caused by impurities (allergens, pollen, and spores) or batch variability. Moreover, the potency of an herbal product may increase the possibility of adverse effects.