What happens when you take digoxin with St. John's wort?
Digoxin is a cardiac glycoside used to slow the heart rate in atrial fibrillation and to give modest support to a weakened heart in heart failure. Unlike most drugs, digoxin is barely touched by the liver's drug-metabolising enzymes. Instead, its absorption and clearance hinge on a transport protein called P-glycoprotein (P-gp), which acts as a pump in the gut wall, bile ducts, and kidney tubules. St. John's wort (Hypericum perforatum) is a popular over-the-counter herb for low mood whose main active constituent, hyperforin, switches on a cellular sensor (the PXR receptor) that ramps up production of P-gp in the intestine.
- Hyperforin activates PXR. Taking St. John's wort over days to weeks tells the gut to make more P-glycoprotein.
- The gut pump gets stronger. Because digoxin relies almost entirely on this transporter, the extra pumping capacity matters a great deal for it specifically.
- Less digoxin gets absorbed. Newly absorbed digoxin is pushed back out into the intestine before it can reach the bloodstream, so blood levels fall.
- The change builds and reverses slowly. The effect develops over roughly two weeks of herb use and takes a similar period to fade after stopping, so digoxin levels drift down and then back up on that timeline.
Two controlled human studies in healthy volunteers (Johne and colleagues; Gurley and colleagues) confirmed this direction: standardised St. John's wort lowered digoxin exposure to a clinically meaningful degree.
Why is this important?
Digoxin has a narrow margin between too little and too much. Even a modest fall in blood level can move a patient from an effective dose to an ineffective one. In practice that means the heart rate in atrial fibrillation may speed up again, with a return of palpitations and an irregular fast pulse, or heart failure symptoms such as breathlessness and swelling may worsen.
The reverse situation is also a real hazard. If a dose was quietly raised to compensate while St. John's wort was on board, then the herb is stopped, P-gp production returns to normal and digoxin levels climb back up. That can tip a patient into digoxin toxicity, which can cause nausea, visual disturbances, confusion, and dangerous heart rhythm problems.
This interaction is easy to miss. Many people do not think of a herbal supplement as a drug and leave it off their medication list. A digoxin level that is drifting downward for no obvious reason should prompt a direct question about herbal and over-the-counter products.
What should you do?
Do not take St. John's wort while you are on digoxin, and do not start or stop either one on your own. Work the change through with the prescriber managing your heart condition, using roughly this sequence.
- Before any change: Tell your prescriber and pharmacist about any St. John's wort use, including multi-ingredient mood, sleep, or stress products that may contain it. Do not stop digoxin yourself.
- Every day in between: Keep taking digoxin exactly as prescribed while the plan is sorted out, and watch for symptoms in both directions — a fast or irregular pulse and palpitations (too little drug), or nausea, visual changes, and confusion (too much).
- After the change: Once the herb is stopped, your prescriber will want a digoxin level rechecked after enough time has passed for the effect to wash out, and will only rely on a steady level for dosing decisions after that washout. Adjust nothing without their say-so.
If you need help with low mood, choose an evidence-based alternative discussed with your clinician: talking therapy such as CBT, exercise, social support, or a prescription antidepressant chosen for compatibility with your heart medicines.
Which specific products are affected?
St. John's wort products vary widely in how much hyperforin they contain, and higher-hyperforin preparations produce the strongest effect. Lower-hyperforin formulations cause less induction but are still best avoided with digoxin, because hyperforin content varies between batches and label accuracy has been unreliable. The herb also turns up as one ingredient among many in combination sleep, mood, and stress blends, so labels need a careful read.
Digoxin products affected include Lanoxin tablets, Digox tablets, generic digoxin tablets, and pediatric digoxin solution. St. John's wort affects other P-glycoprotein-dependent drugs too, including the anticoagulants dabigatran and edoxaban, the immunosuppressants cyclosporine and tacrolimus, and HIV protease inhibitors — another reason to disclose the herb to every prescriber.
The science behind it
Two independent controlled studies in healthy volunteers support this interaction and agree on its direction. Johne and colleagues ran a single-blind, placebo-controlled pharmacokinetic trial showing that a standardised St. John's wort extract lowered digoxin exposure after about two weeks of dosing. Gurley and colleagues, in a human crossover study comparing several agents, likewise found that St. John's wort reduced digoxin levels through P-glycoprotein induction — placing the herb alongside known inducers in clinical relevance. The magnitude in both was clinically meaningful rather than extreme, but because digoxin's safe range is so narrow, even a moderate change carries weight.
- Johne A, et al. Pharmacokinetic interaction of digoxin with an herbal extract from St John's wort (Hypericum perforatum). Clin Pharmacol Ther. 1999;66(4):338-345. PMID 10546917.
- Gurley BJ, et al. Gauging the clinical significance of P-glycoprotein-mediated herb-drug interactions: comparative effects of St. John's wort, Echinacea, clarithromycin, and rifampin on digoxin pharmacokinetics. Mol Nutr Food Res. 2008;52(7):772-779. PMC2562898.
Frequently Asked Questions
Can I take St. John's wort with digoxin if I keep the dose low?
No. There is no reliably safe amount of St. John's wort to combine with digoxin. Hyperforin content varies between products and batches, so even a low-hyperforin product can affect your levels unpredictably. Avoid the combination.
Why does St. John's wort lower digoxin but not affect every drug the same way?
Digoxin is unusual in depending almost entirely on the P-glycoprotein transporter rather than liver metabolism. St. John's wort strongly boosts that transporter, so digoxin is hit harder than drugs cleared by other routes.
How long does the effect last after I stop the herb?
The transporter returns to normal gradually over roughly two weeks. That is why your prescriber waits for a washout period before trusting a steady digoxin level for any dose decision.
What symptoms suggest my digoxin level has dropped?
A return of a fast or irregular pulse, palpitations, breathlessness, or swelling can signal the drug is no longer working well. Report these to your prescriber rather than adjusting the dose yourself.
Is it dangerous to just stop the digoxin instead of the herb?
Yes. Stopping digoxin on your own can let your heart condition flare. The correct move is to stop the herb and let your prescriber recheck and manage the digoxin.
Should I mention St. John's wort even if I only take it occasionally?
Yes. Disclose it at every medication review. This interaction is preventable, but only if your prescriber knows the herb is in the picture.
Key takeaways
- St. John's wort induces intestinal P-glycoprotein, the transporter digoxin depends on, lowering digoxin blood levels over about two weeks of use.
- Because digoxin's effective range is narrow, this can cause therapeutic failure — poor rate control in atrial fibrillation or worsening heart failure.
- Stopping the herb after a dose was raised can swing levels back up and cause toxicity, so changes must be managed by your prescriber.
- Avoid the combination entirely; even low-hyperforin products are unreliable.
- Do not stop digoxin on your own — stop the herb, disclose all supplements, and let your doctor or pharmacist recheck levels after a washout.