Is St. John's Wort Safe To Take With Diovan (Valsartan)?
In our latest question and answer, the pharmacist discusses the safety of taking St. John's Wort and Diovan together.
My cardiologist put me on valsartan to strengthen my heart muscle, which has been weakened by PVCs. My ejection fraction (EF) was 40%. I also take metoprolol succinate to regulate the heart rhythm. Is there any likely interaction if I start taking St. John's Wort? I'm finding conflicting information.
Aug 08, 2023- St. John's Wort may speed up how your body breaks down Diovan, potentially making it less effective at treating your blood pressure and heart condition. Research on this interaction is conflicting, with some studies showing a concern while others found no significant effect. You should discuss taking St. John's Wort with your cardiologist before starting it so your doctor can monitor you appropriately.
Answer
Thank you for contacting us! St. John's Wort is one of the most commonly used dietary supplements. Unfortunately, it's known to potentially interact with various medications due to its broad effects on several metabolizing enzymes in the body.
One such enzyme that studies indicate St. John's Wort may affect is Cytochrome P450 2C9 (CYP2C9). It has been reported in some studies as a 'CYP2C9 enzyme inducer'. An inducer is a substance that speeds up the metabolic processes of the body, increasing the rate at which a particular enzyme processes its specific substrate.
Diovan (valsartan), a medication used to treat heart failure and high blood pressure, is classified as a CYP2C9 substrate, meaning it is metabolized by the CYP2C9 enzyme.
If you were to take St. John's Wort along with Diovan, the concern is that it could potentially increase the rate at which Diovan is metabolized. This could lead to decreased levels of the drug in the body, potentially reducing its effectiveness.
Our detailed interaction page provides more insight into this potential interaction.
Conflicting Evidence
It's worth noting that the research on St. John's Wort's effect on CYP2C9 is somewhat conflicting. Some studies suggest it induces CYP2C9 (the linked study reported that St. John's Wort induced the metabolism of warfarin, a CYP2C9 substrate), while other research has found no significant effect on the pharmacokinetics of CYP2C9 substrates.
Guidance
Given this potentially significant interaction, it would be prudent to discuss this with your cardiologist before starting to take St. John's Wort. Overall, until more definitive research is available, caution is advisable when combining St. John's Wort with CYP2C9 substrates like Valsartan, and at the very least, your doctor should be aware of everything you are taking so you can be appropriately monitored.
Final Words
You also mentioned that you are taking metoprolol succinate, a medication used to treat high blood pressure and heart rhythm disorders. This drug is primarily metabolized by different enzymes (CYP2D6), and the interaction with St. John's Wort is likely to be less significant.
I hope this answer was helpful! Thanks again for reaching out.
References & sources
Glossary — Terms in This Answer
- Dietary supplements
- Products containing vitamins, minerals, herbs, or other ingredients taken by mouth to supplement the diet and support health.
- Enzyme inducer
- A substance that speeds up the metabolic processes of the body, causing enzymes to break down drugs faster.
- Cytochrome P450 2C9 (CYP2C9)
- An enzyme in the body responsible for breaking down and eliminating certain medications.
- Substrate
- A substance that is acted upon and broken down by an enzyme.
- Metabolized
- The process by which the body breaks down and processes a drug or substance.
- Pharmacokinetics
- The study of how the body absorbs, distributes, breaks down, and eliminates drugs.
- CYP2D6
- Another enzyme in the body responsible for metabolizing certain medications, different from CYP2C9.
- Cardiologist
- A doctor who specializes in treating diseases and conditions of the heart and blood vessels.
Dr. Brian Staiger, PharmD
Doctor of Pharmacy, board certified clinical pharmacist (BCPS), American Herbalist Guild, Medication Therapy Management certified
Brian Staiger, PharmD, BCPS, is a licensed pharmacist with more than 13 years of experience across retail pharmacy, clinical pharmacy, medication safety, pharmacy program development, and healthcare administration. He is the founder of HelloPharmacist.com, where he helps patients...
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