The most common herb-drug interaction is that between the prescription blood thinning drug Warfarin (Coumadin) and herbs that thin the blood such as Garlic, Onion, Red Clover, Ginger and Ginkgo biloba. Anyone who is taking Coumadin, Warfarin, Heparin, Lovanox, Plavix or other prescription blood-thinning herbs should not attempt to take herbs because the risk is too high for bleeding.They should be supervised by a knowledgeable practitioner who can monitor their PT/PTT/INR levels.
Because herbs can strongly affect physiology, the effect could be too strong if an herb that has a specific effect is taken with medications that also have the same effect. For example, one should not combine stimulating herbs (such as ma huang, coffee, or yohimbe) with a stimulant medication (such as Ritalin).
One shouldn't combine hormone balancing herbs with prescription estrogen / progesterone medications such as birth control pills. Phytoestrogens and plant sterols may reduce the contraceptive effect of birth control pills. One should use caution in this area because there can be too much hormonal stimulation when using both. Women know when this has happened because they experience hot flashes (again). They can lower their dose of herbs or hormonal replacement therapy to compensate and then they are fine. Or if they want to stop the hormone replacement therapy, they can gradually taper the medication while they start and gradually increase the dose of menopausal herbs.
On the other hand, prostate herbs (saw palmetto) don't appear to interact with prostate medications and many men have combined herbs with their prostate medication.
Absorptive substances such as Charcoal and Psyllium as well as mucilaginous herbs such as slippery elm can reduce absorption of medications as well as herbs, but only if taken in the same dose. (We try to avoid these foods/nutrients from our formulations).
Herbs that reduce blood pressure (Garlic, Linden flower, Hawthorne) should be used with caution in those who are taking blood pressure lowering medications. The reason is because the blood pressure can decrease too much, and this results in dizziness and heart palpitations due to low blood pressure. However, if one monitors the blood pressure regularly while taking these herbs, one will see the blood pressure coming down and decrease either the medication or the herbs before any symptoms of low blood pressure appear – but why reduce the food that heal?
Chemotherapy and herbs normally works well.
In short, your (especially chronic) medication were prescribed to help control disease symptoms and functional food / herbs can enhance that effect as well as improve the body’s own biochemical processes. This imply that you will have to consult your physician to adjust medication dosages over time – especially for blood thinning medication. Remember you take a headache pill only when you have a headache!