Herb and Pharmaceutical Drug Interactions: What You Need To Know

Medical Disclaimer: The information in this article is meant for educational purposes and is not meant to replace care from your primary caregiver (Medical doctor, Naturopathic doctor) and healthcare team. Consult with your primary caregiver and/or a Registered Herbalist before taking herbs and pharmaceuticals together to make sure they suit your constitution type and will not interact with any medications you’re taking.

Is it still safe to take herbs if I’m on a pharmaceutical medication? 

I get asked this question all the time, and it’s an important consideration when you’re thinking about adding herbs to your healing regimen. 

The short answer is, IT DEPENDS! Some herbs interfere with medications, others may have no impact on the medication at all making them totally safe to take and the more interesting interaction is that some herbs actually make certain medications MORE effective than if you were to take them on their own. 

Before we delve into this further, I do want to say that generally speaking herbs are safe, gentle and effective medicines that work in harmony with the body to support organ systems and increase well-being. However, they’re also very potent medicine! When you add other potent medicines like pharmaceutical medications into the picture, it’s especially important to make sure they are compatible. 

Because there are so many medicinal herbs one could take, and even more pharmaceutical medications, this isn’t a subject to venture out on your own with (see medical disclaimer above). ALWAYS talk to a trusted health care provider before taking herbs alongside your pharmaceuticals. In this case, I highly recommend you specifically seek out and work with a clinical herbalist, as we’re trained to know the contraindications of each herb, which includes what medications each herb potentially interacts with. Unfortunately, doctors aren’t trained in herbal medicine, so aren’t the best resource for this specific subject. There are some really great pharmacists that know their stuff! But again, it depends on the pharmacist. Herbalists are by far the experts when it comes to knowing what herbs will interact (and how they’ll interact) with pharmaceutical medications. 

The Traffic Light Approach to Herb-Drug Interactions

Undesirable Pharmaceutical Drug-Herb Interactions 


The following interactions are ones to keep an eye out for as you’d want to avoid them, generally speaking. 

The “Duplicate Action” Interaction 

This interaction occurs when the herb you’re taking has the exact same effect in the body as the pharmaceutical drug. Let’s say you’re on a medication that helps to lower your blood pressure (Examples might be diuretics, beta-blockers, ACE inhibitors, angiotensin II receptor blockers or calcium channel blockers). In addition to taking the medication to manage your hypertension, you think it would be super smart of you to support the health of your blood vessels and circulation with herbs over the long term to minimize health complications down the road (you’d be right, that’s a great idea!). Here’s where you would need to be cautious- many of the herbs that support cardiovascular health such as Hawthorn (Cratageus spp.) can ALSO reduce blood pressure! Now, this is a good thing generally speaking, especially if you’re not taking medication and are looking for this effect! 

However, by having the same action in the body as the pharmaceutical drug, you may experience the “duplicate action” interaction, which causes a stronger physiological effect than desired, and in this case could cause your blood pressure to go TOO LOW, resulting in hypo-tension. At this point you have a few options- you can stop taking the herb and continue with medication only, or you can work with your doctor and herbalist to gradually decrease the blood pressure medication while increasing the herbs (if this is a medically safe option for you). Another option is to stop taking the herb(s) that directly affect blood pressure and incorporate herbs that can improve the strength of your blood vessels without impacting blood pressure directly such as Bilberry (Vaccinium myrtillus), Gotu kola (Centella asiatica) or Ginkgo (Ginkgo biloba), for example. Of course, first checking that these don’t have any other contraindications for you.

Never go off your medications without first consulting with your family doctor, naturopath and/or herbalist. 

The “Opposite Action” Interaction 

This is when a herb has the opposite effect as a pharmaceutical medication, potentially rendering the pharmaceutical drug less effective.

For example, if you’re taking a cough suppressant at night so you can sleep, don’t take herbs that will encourage you to expectorate (cough up mucus) before bed! Now a great strategy is to take expectorant herbs during the day to clear out the infection or congestion and then take a soothing, antispasmodic herbal blend that will calm the cough reflex at night so you can get a good night’s sleep. 

This is a pretty strait forward interaction that you want to be mindful of when taking herbs alongside a medication. 

The “CYP-450 Liver Pathway” Interaction 

Pharmaceutical drugs and herbs alike are metabolized in the body through specific organ systems so they can take their medicinal effect and then be eliminated. 

How a herb or drug is metabolized is very important when it comes to herb-drug interactions, especially when it comes to CYP-450. 

What is CYP-450? 

Cytochrome P450’s are a superfamily of enzymes responsible for the metabolism of many medications (and herbs) through the liver. Although this class has more than 50 enzymes, six of these enzymes are responsible for metabolizing 90 percent of pharmaceutical drugs (1). 

We can go down a huge rabbit hole here discussing the intricacies of this very complex system. However, I’m going to stay away from that and keep it simple. 

Before we delve in though, one more interesting geeky-science side note: Genetic variability (polymorphisms) in these enzymes from one person to another can influence how you respond to pharmaceutical drugs, including pain medications, antidepressants and beta blockers. So if you’ve ever wondered why you’re SO sensitive to pharmaceutical drugs compared to others, or you feel like you take a truck load of pain medication and it doesn’t touch the pain, your genes related to these enzymes may be why! (I don’t recommend taking a truck load of pain medication, obviously! This is just to illustrate a point). 

To hit this point home, according to the American Academy of Family Physicians: “One out of every 15 white or black persons may have an exaggerated response to standard doses of beta blockers (e.g., metoprolol [Lopressor]), or no response to the analgesic tramadol (Ultram). This is because drug metabolism via CYP450 enzymes exhibits genetic variability (polymorphism) that influences a patient's response to a particular drug.” (1) 

Ok, back to simplicity.

This CYP-450 is a BIG DEAL in the medical world as well, because drug-drug interactions are very common and can cause seriously harmful effects.  

Why does this matter for herb-drug interactions? 

CYP-450 Inducers: Quicker Metabolism, Less Effective Drugs

Let’s say you’re taking a medication that is metabolized through the CYP-450 pathway in the liver and then you introduce a herb that induces CYP-450 liver enzymes. Inducing essentially means the herb will be activating these enzymes and gets them clearing out the medication at a faster rate than normal. This means the drug isn’t in your system long enough or at the required dose to take its desired effect. The medical community calls this “therapeutic failure.”

CYP-450 inducers can increase the rate of a drug’s metabolism by as much as two to threefold, which can develop over the period of a week or more (4). Simply put, CYP-450 inducers render the medication less effective. 

A very well-known herbal CYP-450 inducer is St-John’s Wort (Hypericum perforatum). One of its active ingredients (hyperforin) acts on these liver enzymes which reduces the oral bioavailability of many drugs making them less effective (5). 

CYP-450 Inhibitors: Slower Metabolism, Potentiates Drugs 

Now on the flip side, let’s say you’re taking a drug that is metabolized through CYP-450 and you introduce a herb that inhibits the CYP-450 liver enzymes. This means the enzymes are slowed down, don’t work as quickly and can potentiate a drug beyond the desired dose. 

Simply put, CYP-450 inhibitors slow down drug metabolism, making the drug stay in your system longer or at a higher dose than desired. This renders a drug more potent than anticipated and can create adverse health effects. 

A really commonly known CYP-450 inhibitor is grapefruit juice and people on certain medications need to avoid it in order to keep their medication dose correct. 

Important to Note: Not all CYP-mediated herb-drug interactions are clinically significant. The clinical significance of CYP-mediated interactions can be more concerning in relation to drugs with a narrow therapeutic window (meaning the medication is dose-critical and any change in the dose can greatly impact symptoms and health effects) (3). 

Many herbs don’t act on these liver pathways! Available research indicates that, at commonly recommended doses, many other herbs including Echinacea, Ginkgo biloba, Garlic, Goldenseal and Milk thistle DO NOT act as potent or moderate inhibitors or inducers of CYP enzymes (5). 

All this to say, CYP-450 isn’t an issue for many herbs, but it’s important to make sure! 

Herbs That Can Safely Be Taken at the Same Time as Pharmaceutical Medications

Traffic Light: YELLOW (Proceed with Caution)

The reason this light isn’t green right off the bat is because you always want to double check that a herb is well-suited to your unique health situation. Once you’ve slowed down to assess whether there are any undesired effects (back to the traffic light reference) and you make sure it’s safe, you’re good to go when that light turns a nice bright green!  There are PLENTY of herbs (the majority of them) that are safe and gentle to be taken alongside pharmaceutical medications without needing to worry about them interacting. 

I know we’ve focused a lot on the herb-drug interactions that are “negative”, but the truth is there are SO MANY herbs you can safely take while on medication, it’s just a matter of figuring out which ones are a good match and which ones are best to avoid. 

Herbs That Enhance Pharmaceutical Interventions to Make Them MORE Effective

Traffic Light: GREEN! 


Ok, this is by far the more interesting and coolest part of herb-drug interactions. There are some herbs that, when used alongside pharmaceutical medication or interventions, actually INCREASE the effectiveness of the treatment. 

Astragalus (Astragalus membranaceous), due to its beneficial effects on the immune system, has been found to be “ a useful adjuvant during chemotherapy, raising white cell counts between treatments, and after radiotherapy or surgery” (2).  This is a big deal because if you’re going to go through the grueling and challenging treatment of chemotherapy to treat your cancer, and you can’t continue if your white blood cell count goes too low, you go through all of that in vain. So taking Astragalus at the same time actually allows you to continue with the treatment plan so you can see it through to the end (if white blood cell count is the reason you'd have had to stop). There’s another study where Astragalus was beneficial for patients with small cell lung cancer. They  underwent “long-term treatment with chemotherapy, radiotherapy, immunotherapy and herbal medicine consisting of Panax ginseng leaf and Astragalus root in an open trial. The combined treatment raised the survival rates considerably, with some patients gaining 3 to 17 years in survival.” 

This is an incredible example of how when used in union, conventional medical interventions and herbal medicine can increase the effectiveness of the treatment protocol, benefiting the patient beyond what they would have received from only herbal or conventional treatment alone. 

Similar studies have been conducted for Reishi with concurrent use during chemotherapy. From a holistic standpoint, taking Reishi alongside anti-viral and antimicrobial medications (Acyclovir and Cefazolin) is recommended for immunocompromised patients with chronic viral and microbial infection due to its synergistic effect with the medication (6).

Here’s another amazing example… 

Ever heard of MRSA? It stands for Methicillin-resistant Staphylococcus aureus, which is a bacteria that has evolved to NOT respond to certain antibiotic treatments, making it a very hard infection to treat. But get this, herbs that contain berberine (a naturally occurring antibacterial phytochemical that is bright yellow in color) can actually work synergistically with certain antibiotics to make them effective at treating MRSA again! How wild is that?  

In a study looking at the combination of berberine-containing herbs and antibiotics the authors concluded: “An additive effect was found between berberine and ampicillin, and a synergistic effect was found between berberine and oxacillin against MRSA.” (6)

Herbs that contain berberine in Western Herbal Medicine  include: Goldenseal (Hydrastis canadensis), Barberry (Berberis vulgaris) and Oregon Graperoot (Mahonia spp.). 

An Important Note on Individuality:

Every person has a unique physiology and therefore will respond in their own unique way to herb-drug interactions. Like I mentioned above, a variety of factors including genetics can determine how each person responds to medication and/or herbs. Not everyone will experience the same effects. We’ve discussed broad generalizations of potential interactions, but at the end of the day the effects need to be monitored by a qualified health professional to gauge if an interaction is of concern, or not. How this might look clinically: In the example of blood pressure medications and herbs, blood pressure would be monitored consistently over a specific time period to determine whether or not it’s dipping too low, or if it’s staying in a healthy range. If it’s still within a good range, there may be no reason for concern and the herb and drug can continue to be taken together. Again, this always needs to be determined on a case by case basis, working closely with your health care providers so you can get the best of the pharmaceutical and herbal medicine world to support your health!

A big factor in herbal interactions is that unfortunately there’s often a lack of scientific studies to prove the interactions between herbs and drugs. This means there are a lot of  “theoretical interactions” based on the mechanisms of action of the herb (and the drug in question). However, it's still important to take these theoretical interactions seriously and monitor how your body is responding. 

As a herbalist, it’s always my intention to work WITH you, wherever you’re at in your health journey. That includes working with the pharmaceutical medications you’re on and choosing herbs that can benefit your health and symptoms safely and effectively. Pharmaceutical medications can be life-changing! I believe we can access the best of both worlds and access the long-term healing powers of plants, alongside conventional medications where necessary. To work with me, contact me here!

About the Author:

Bree Nabholz is a Registered Herbalist and the owner of Wild Yarrow Herbal Medicine Clinic & Dispensary in Edmonton, Alberta. In addition to seeing clients in her private practice, Bree is an instructor at Pacific Rim College and Wild Rose College, where she teaches business, herbal energetics and runs clinical apprenticeships. She works with Naturopaths and midwives to design custom herbal blends for their patients and offers herbal workshops & online herbal medicine courses. Bree sat on the board of the Alberta Herbalist Association (AHA), as well as the Canadian Council of Herbalist Associations (CCHA) for 3 years and is a Registered Professional Member of the Alberta Herbalist Association and the American Herbalists Guild.


What about you? Do you take any herbs alongside pharmaceutical medication that you know are compatible to improve your symptoms and health? 

Tell me in the comments below! 


1) American Academy of Family Physicians:  The Effect of Cytochrome P450 Metabolism on Drug Response, Interactions, and Adverse Effects 

2) Mills S, Bone K. (2012) Principles and Practice of Phytotherapy: Modern Herbal Medicine (2nd edition). Edinburgh: Churchill Livingstone.

3) McDonnell, A. M., & Dang, C. H. (2013). Basic review of the cytochrome p450 system. Journal of the advanced practitioner in oncology, 4(4), 263–268. 

4) David’s Drug Guide: The Cytochrome P450 System: What Is It and Why Should I Care?

5) Wanwimolruk, S., & Prachayasittikul, V. (2014). Cytochrome P450 enzyme mediated herbal drug interactions (Part 1). EXCLI journal, 13, 347–391.

6) Stargrove,M., Treasure, J. & McKee, D. (2008). Herb, Nutrient, and Drug Interactions: Clinical Implications and Therapeutic Strategies. 

7) Yu, H-H. Et al. Antimicrobial Activity of Berberine Alone and in Combination with Ampicillin or Oxacillin Against Methicillin-Resistant Staphylococcus aureus (2005). Journal of Food Medicine, 8(4):454-61

1 comment

  • Hi Bree, great article. I have always taken Melatonin alongside my anti-dep meds and recently added Valerian as well. I have always experimented! I did not know about CYP-450, have never heard of this interaction before. I usually know if something isn’t working and shy away from spending too much time in the chair. I am not big on pharm. But I couldn’t live without the Zol. Thanks for sharing!


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