A mineralocorticoid (adrenal salt-retaining hormone)
Fludrocortisone
A steroid that replaces the body’s salt-retaining hormone — used mainly in adrenal insufficiency (Addison’s disease) and for some causes of low blood pressure on standing.
What is Fludrocortisone?
Fludrocortisone is a steroid that acts like aldosterone, the body’s salt-and-water-retaining hormone. It is used to replace this hormone in adrenal insufficiency (Addison’s disease), usually alongside a steroid such as hydrocortisone, and to help certain kinds of low blood pressure on standing. Because it makes the body hold on to salt and water and lose potassium, blood pressure and potassium are monitored.
Education and reference only. This is a plain-language guide to Fludrocortisone — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Fludrocortisone is a synthetic steroid that mimics aldosterone, the adrenal-gland hormone that controls the body’s salt and water balance. Its main use is as hormone replacement in people whose adrenal glands do not make enough of their own — most commonly Addison’s disease — where it is given alongside a glucocorticoid steroid such as hydrocortisone. It is also used for some forms of low blood pressure on standing (postural hypotension) and salt-losing conditions. It is taken as a small daily tablet.
How it works
Fludrocortisone acts on the kidneys in the same way as the natural hormone aldosterone: it tells them to hold on to sodium (salt) and water and to get rid of potassium. This raises the circulating blood volume and supports blood pressure. In adrenal insufficiency it replaces the missing salt-retaining hormone; in postural hypotension it expands blood volume so that blood pressure is better maintained when a person stands up.
What it treats
Conditions Fludrocortisone is used for
Practical use
How to take Fludrocortisone
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it once a day as prescribed — usually a small tablet — and do not stop it suddenly.
- If you have adrenal insufficiency, keep taking your glucocorticoid (e.g. hydrocortisone) as well, and follow "sick-day rules" to increase steroids during illness or injury.
- Carry a steroid emergency card and tell any healthcare professional you take it.
- Attend checks of blood pressure and potassium so the amount can be fine-tuned.
- Report significant ankle swelling, breathlessness, or muscle weakness/cramps (which can signal low potassium).
Weighing it up
Advantages & disadvantages of Fludrocortisone
Advantages
- Replaces a vital hormone in adrenal insufficiency, restoring normal salt and water balance.
- Effective for some difficult cases of low blood pressure on standing.
- A small once-daily tablet.
Disadvantages
- Can raise blood pressure and cause fluid retention and low potassium if the amount is too high.
- Needs monitoring and dose balancing, and must not be stopped abruptly.
- Part of a treatment plan that also requires glucocorticoid steroids in adrenal insufficiency.
Practical use
Good to know
Because fludrocortisone makes the body retain salt and water, it can raise blood pressure and cause swelling if the amount is too high, and it lowers potassium — so blood pressure and potassium are checked and the amount is adjusted to get the balance right. In adrenal insufficiency it is only one part of treatment: the glucocorticoid (such as hydrocortisone) must also be taken, and both may need to be increased during illness, injury or surgery ("sick-day rules"). People on long-term replacement carry a steroid emergency card. It should never be stopped suddenly.
Who should not take it / use with caution
- People with untreated infections, and used with great care in heart failure or high blood pressure.
- People with a low potassium level until corrected.
- It is used cautiously and individually in pregnancy, under specialist care.
Monitoring
- Blood pressure
- Blood potassium (and sodium)
- Signs of fluid retention; symptom control
Side effects
- From too much: raised blood pressure, fluid retention and swelling, and a low potassium level (weakness, cramps).
- From too little (in adrenal insufficiency): tiredness, dizziness on standing, salt craving and low blood pressure.
- Long-term high amounts can carry the general effects of steroids.
Key interactions
- Medicines and foods that lower potassium (some diuretics, liquorice) add to the risk of low potassium.
- It can reduce the effect of blood-pressure-lowering medicines.
- Its effect on potassium matters alongside digoxin (low potassium increases digoxin toxicity).
Available as: Tablets (small strength).
Answers
Fludrocortisone: frequently asked questions
Is fludrocortisone the same as my hydrocortisone?
No — they do different jobs. Hydrocortisone (a glucocorticoid) replaces the body’s stress/steroid hormone, while fludrocortisone (a mineralocorticoid) replaces the salt-and-water-balancing hormone. In Addison’s disease most people need both, and you should not stop either without advice.
Do I need more during illness?
In adrenal insufficiency, yes — the glucocorticoid part of your treatment (such as hydrocortisone) usually needs increasing during illness, injury or surgery ("sick-day rules"). Fludrocortisone itself is often kept the same, but follow the specific plan your endocrine team has given you and carry your steroid emergency card.
Why do I need my potassium checked?
Fludrocortisone makes the body lose potassium as it holds on to salt and water. If the amount is too high your potassium can fall too low, causing muscle weakness or cramps; if too low, potassium can rise. Blood tests let the dose be balanced correctly.
Can I stop it if I feel well?
No — do not stop suddenly. In adrenal insufficiency these hormones are replacing something your body cannot make, and stopping can cause a dangerous adrenal crisis. Any change must be made with your specialist team.
Authoritative sources
- BNF: Fludrocortisone acetate.
- electronic Medicines Compendium (SmPC): Fludrocortisone (Florinef).
- NICE CKS: Addison’s disease.
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