Digoxin: what it does and what to watch
Also known as: Cardiac glycoside, Heart rhythm medicine · Cardiac glycoside · Updated 2026-08-20 · Educational — not medical advice
In plain language: This medicine increases the force of heart muscle contraction and slows the electrical signals passing through part of the heart, by affecting a pump on heart cell membranes that regulates sodium and calcium levels inside cells. Because the gap between a helpful blood level and a toxic one is quite narrow, careful monitoring is an important part of treatment.
What it's used for
- Managing certain irregular heart rhythms such as atrial fibrillation
- Supporting heart function in some cases of heart failure
- Controlling heart rate when other treatments aren't suitable or sufficient
Common side effects
- Nausea
- Loss of appetite
- Fatigue
- Mild visual changes
- Headache
Get medical help if…
Toxicity causing more pronounced nausea and vomiting, visual disturbances such as seeing halos or altered colour vision, and dangerous heart rhythm changes
Low potassium levels can make the heart much more sensitive to this medicine's effects, increasing toxicity risk even at usual blood levels of the medicine
Slow or irregular heartbeat requiring urgent evaluation
Lab values it can move
Few guides tell you this part: medicines show up in blood work. If you take Digoxin and a value below looks off on your report, this may be part of the story — never stop a medicine without your doctor.
Low potassium significantly increases the risk of toxicity from this medicine, so levels are checked regularly, especially alongside diuretics.
PotassiumThis medicine is cleared largely through the kidneys, so creatinine is checked to guide safe dosing.
CreatinineReduced kidney filtering capacity means the medicine is cleared more slowly, raising the risk of buildup and toxicity if dosing isn't adjusted.
eGFR (Estimated Glomerular Filtration Rate)Good to know
- This medicine has a narrow therapeutic window, meaning the gap between a helpful level and a toxic level in the blood is small, so blood levels and kidney function are monitored periodically
- Report nausea, vomiting, visual halos or colour changes, or a noticeably irregular or very slow pulse promptly
- Low blood potassium, which can happen with some diuretics or with vomiting and diarrhea, increases the risk of toxicity even without any change in dose, so potassium levels are checked regularly
- Kidney function affects how this medicine is cleared from the body, so dosing is adjusted for reduced kidney function
- Many other medicines interact with this one, so all medicines should be reviewed with a prescriber before starting or stopping anything
Questions people ask
What does 'narrow therapeutic window' mean for this medicine?
It means the difference between a blood level that helps the heart and one that causes toxicity is quite small, unlike many other medicines where there is more room for error. This is why blood tests to check the medicine level, alongside kidney function and potassium, are done periodically, and why any dose changes need close medical guidance.
Why does low potassium matter so much with this medicine?
This medicine works partly by affecting the same cell pump that potassium also uses, so when blood potassium is low, the heart becomes more sensitive to this medicine's effects even if the medicine level itself is normal. This can trigger toxicity symptoms and dangerous heart rhythms, which is why potassium is monitored closely, especially with certain diuretics.
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