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Herbs and Cytochrome P450 Enzymes

The importance of safety when using herbs in a therapeutic or medicinal setting is vital to ensure a safe outcome that is desired. Many herbs have contraindications for specific things such as not using during pregnancy or if the individual is nursing, not using if the person is on specific medications, as well as age restrictions for specific herbs. One contraindication that I found really interesting in my Herbal Materia Medica classes is the importance of safety for clients who are taking medications that are metabolized by the cytochrome P450 enzyme.

The cytochrome P450 is a group of enzymes that are involved in phase I detoxification which is a process that involves the liver. According to Michael T. Murray, N.D., the author of The Encyclopedia of Natural Medicine, this detoxification process neutralizes unwanted chemical compounds from our body such as drugs, pesticides, toxins from the gut, as well as hormones and inflammatory chemicals. This process is what keeps these compounds from building up in the system and becoming toxic. The cytochrome P450 system is made up of up to 100 different enzymes. (Murray, 2012, p. 116) Certain herbs are known to inhibit the cytochrome P450 system, which in turn makes it to where the individual is not metabolizing their medications properly and these medications can build up in the system and become toxic and very dangerous. Some of the pharmaceutical drugs that inhibit the Phase I detoxification process include benzodiazepines, antihistamines, cimetidine, ketoconazole, and sulfaphenazole. Other contributors in the inhibiting of this process can include foods such as grapefruit juice (due to naringenin), turmeric (due to curcumin), red chili peppers (due to capsaicin), and clove oil (due to eugenol). Other factors include toxins from bad bacteria in the gastrointestinal system, and aging. (Murray, 2012, p. 119)

Grapefruit Juice and Medicine

Herbs that support the liver are termed hepatic herbs. These herbs can strengthen, cleanse, tone, and regulate the secretion of bile. It can support the liver in the detoxification process. But, despite being supportive to this important organ, for individuals on certain medications it can have an unwanted effect. Let’s take a look at dandelion (Taraxacum officinale). Dandelion is a very common and popular herb amongst herbalists because it makes a wonderful substitute for coffee, it is high in potassium and other beneficial constituents, and is great as a bitter tonic herb to support the digestive system. (Petersen, 2018) Unfortunately, dandelion has shown evidence to researchers that it might inhibit the cytochrome P450 IA2. (Maliakal PP and Wanwimolruk S, 2011) Although not reported in humans, it is still important. Pharmaceutical drugs that are metabolized by CYPIA2 include Elavil, Haldol, Zofran, Inderal, Isoptin, and several others. So it is highly advised that people who are taking these types of medications be cautious when using dandelion.

Dandelion Taraxacum officinale

Another popular medicinal herb is goldenseal (Hydrastis canadensis). Herbalists enjoy using goldenseal due to the alkaloids of hydrastine and berberine because they have therapeutic actions of being an antibiotic, antiseptic, and antispasmodic. Hydrastine is also a natural styptic so goldenseal can be used for cuts and scrapes to help stop bleeding. Goldenseal has a mild to moderate effect on the liver enzyme CYP3A4, which is responsible for metabolizing many pharmaceutical drugs which include antidepressants, antivirals, and anxiolytics. Goldenseal can inhibit this liver enzyme which can potentially cause these medications to not metabolize properly in the body and build up over time and become toxic. (Petersen, 2018, p. 337) (NCBI, 2014)

Another common herb that can affect the cytochrome P450 enzymes is turmeric (Curcuma longa). A study that was done on lactating mice and translactationally exposed mouse pups showed that turmeric and curcumin significantly elevated cytochrome b5 and cytochrome P450. So with turmeric, instead of inhibiting these enzymes, it elevates their process. This can be harmful to individuals taking medications that are metabolized via those pathways because the liver will then metabolize the medications too rapidly and then they are excreted. So for instance, if a person is needing 25mg of a certain pharmaceutical drug, and that drug is metabolized too rapidly, the medication will not be as effective as needed and they might need a higher dosage and feel that their medication is not working. (Bone & Mills, 2013, p. 910)

Turmeric Curcuma longa

To conclude, although herbal preparations can be generously effective in supporting our body systems, that support can also be inhibitory in a negative way that can effect individuals taking certain pharmaceutical drugs. This shows the importance of working with a qualified and/or registered herbalist so they can do a thorough intake of your medical history and any medications that you may be taking that can be impacted by the use of herbs.


Bone, K., & Mills, S. (2013). Principles and practice of phytotherapy: Modern herbal medicine (2nd ed.). Edinburgh: Churchill Livingstone/Elsevier.

Heinrich, M. (2014). Fundamentals of pharmacognosy and phytotherapy (2nd ed.). Edinburgh: Elsevier.

Maliakal PP and Wanwimolruk S. (2011, October). Effect of herbal teas on hepatic drug metabolizing enzymes in rats. - PubMed - NCBI. Retrieved from

Murray, M. T. (2012). The encyclopedia of natural medicine third edition (3rd ed.). New York, NY: Atria Books.

NCBI. (2014, April 2). Cytochrome P450 enzyme mediated herbal drug interactions (Part 1). Retrieved from

Petersen, D. (2018). Hepatic Herbs. In HERB 303 Herbal Materia Medica II (18th ed.). Portland, OR: American College of Healthcare Sciences.



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