What happens when you take carvedilol with st. john's wort?
Carvedilol is a beta-blocker with added alpha-blocking activity, used mainly for heart failure, high blood pressure, and protection after a heart attack. St. John's Wort (Hypericum perforatum) is an herbal product taken for low mood. The concern when they are combined is that the herb can speed up how fast the body clears carvedilol, leaving less of the drug to do its job.
- Carvedilol is partly handled by liver enzymes and a transporter. The drug is broken down by liver enzymes such as CYP2C9 and CYP3A4, and it is also moved by P-glycoprotein, a transporter that controls how much drug is absorbed from the gut.
- St. John's Wort switches those systems on. A compound in the herb called hyperforin activates a receptor in the liver and intestine that increases production of CYP3A4, CYP2C9, CYP2C19, and P-glycoprotein. This effect builds up over a couple of weeks of regular use.
- Carvedilol clears faster. With more enzyme and transporter activity, carvedilol is broken down and pushed out more quickly, so its blood levels tend to fall.
- The beta-blocker effect may weaken. Lower carvedilol levels can mean less blood-pressure control and less heart-rate slowing than the prescribed dose was meant to provide.
It is worth being clear about the strength of this evidence. No study has directly measured carvedilol levels in people also taking St. John's Wort. The concern is extrapolated from the herb's well-documented effect on other drugs handled by the same enzymes and transporter. It is a reasonable, mechanism-based caution rather than a proven, quantified drop.
Why is this important?
Carvedilol is not a comfort medicine. In heart failure, getting an adequate amount of beta-blocker is part of what improves outcomes, so anything that quietly lowers the drug's level is worth taking seriously. In high blood pressure and after a heart attack, weaker beta-blockade over time can mean less protection than intended.
The bigger practical problem is that this interaction is easy to miss. St. John's Wort is sold in grocery and health-food stores as a mood supplement, so people often do not mention it to their cardiologist, and the pharmacy may never see it. The herb's enzyme-boosting effect also builds slowly over a couple of weeks and fades slowly after stopping, so a patient can look like they simply need a higher carvedilol dose when the real cause is the supplement.
That said, this is a moderate-severity interaction, not an emergency. It calls for awareness and monitoring, not alarm.
What should you do?
The simplest approach is to keep the two apart and to keep your prescriber informed.
- Before any change (starting either one): Do not begin St. John's Wort while you are on carvedilol. Tell your cardiologist or primary-care provider about every supplement and herbal product you take, including mood-support, weight-loss, and bodybuilding stacks, which sometimes contain St. John's Wort under unfamiliar names.
- Every day while on both: If you are already taking the two together, keep taking your carvedilol as prescribed and do not stop the herb abruptly on your own, especially if you started it for low mood. Watching your blood pressure and heart rate at home gives your prescriber useful information.
- After a change (stopping the herb or adjusting either drug): Raise the combination at your next visit before changing anything. Because the herb's effect fades over a couple of weeks after you stop it, your effective carvedilol exposure may rise again during that time, so your prescriber may want to check your blood pressure and heart rate more closely.
If carvedilol seems less effective than it used to be, review every supplement with your doctor and pharmacist rather than assuming you need a higher dose. Removing the herb is usually preferred over raising the carvedilol dose, because the underlying condition has not changed.
Which specific products are affected?
Carvedilol is sold as Coreg (immediate release) and Coreg CR (controlled release), along with many generics. Both are handled by the same enzymes and transporter, so the same caution applies to either.
St. John's Wort is sold under many brand names as capsules, tablets, tinctures, and teas. Products differ in how much active compound they contain, and labels are not always reliable, so the prudent assumption is that any St. John's Wort product can have this enzyme-boosting effect.
Other beta-blockers handled by liver enzymes, such as metoprolol and propranolol, may also be affected by St. John's Wort to varying degrees. Atenolol, which is mostly removed unchanged by the kidneys, is less likely to be affected, though transporter effects could still play a small role.
The science behind it
The direction of this interaction is plausible and supported by authoritative drug information, but it rests on mechanism and extrapolation rather than a direct human study of the pair.
MedlinePlus, the NIH/NLM consumer drug reference, lists St. John's Wort among the herbal products that interact with carvedilol (medlineplus.gov).
A 2020 review of St. John's Wort drug interactions (Nicolussi S, et al. Br J Pharmacol. 2020;177(6):1212-1226, PMID 31742659) confirms the herb induces CYP3A4, CYP2C9, CYP2C19, and P-glycoprotein. Notably, it does not meaningfully induce CYP2D6 or CYP1A2, which is why claims that the herb hits every enzyme carvedilol uses are overstated.
Carvedilol is itself handled by liver enzymes and the P-glycoprotein transporter, overlapping with some but not all of the systems St. John's Wort induces. The overlap is enough to expect some reduction in carvedilol exposure, but the absence of a direct pharmacokinetic study is why this is treated as a moderate, mechanism-based caution rather than a high-severity, quantified effect.
Frequently Asked Questions
Does St. John's Wort make carvedilol stop working?
It is unlikely to switch the drug off, but it can lower carvedilol's blood levels enough to weaken its blood-pressure and heart-rate effects. The size of that drop has not been measured directly for this pair.
Is this a dangerous combination?
It is considered a moderate interaction. It is worth avoiding and worth monitoring, but it is not the kind of emergency that requires you to stop your heart medicine on your own.
I just realized I've been taking both. What should I do?
Keep taking your carvedilol as prescribed and do not stop the herb abruptly. Bring it up with your cardiologist or pharmacist so they can decide whether to taper the herb and watch your blood pressure and heart rate.
How long does the effect last after I stop St. John's Wort?
The herb's enzyme-boosting effect builds over about a couple of weeks and fades over a similar period after stopping, so your carvedilol levels may shift gradually during that time.
Are other beta-blockers safer with St. John's Wort?
Atenolol, which the kidneys clear mostly unchanged, is less likely to be affected. Metoprolol and propranolol are handled by liver enzymes and may also interact. Your prescriber can advise on the best fit for you.
Can I take them a few hours apart to avoid the problem?
No. This interaction works by changing enzyme and transporter levels over days, not by the two products meeting in the gut, so spacing the doses apart does not prevent it.
Key takeaways
- St. John's Wort can speed up how the body clears carvedilol, which may lower its levels and weaken its blood-pressure and heart-rate effects.
- This is a moderate, mechanism-based caution: no direct human study of the pair exists, and the herb does not affect every enzyme carvedilol uses.
- Do not start St. John's Wort while on carvedilol, and tell your prescriber about every supplement you take.
- If you already take both, do not stop the herb abruptly; raise it at your next visit and review with your doctor or pharmacist.