Short answer: The Aldactone label names gynecomastia (breast enlargement in men) as the most common side effect; about 9% of men on a mean 26 mg a day developed it in the RALES heart failure trial. The label's main warnings are high potassium, low blood pressure with worsening kidney function, and other salt and blood sugar changes. Aldactone has no boxed warning.
What Aldactone is approved for: Aldactone is an aldosterone antagonist approved to treat NYHA Class III to IV heart failure with reduced ejection fraction (to increase survival, manage edema and reduce heart failure hospitalization), as add-on treatment for high blood pressure, for edema from liver cirrhosis or nephrotic syndrome that has not responded to other measures, and for primary hyperaldosteronism (section 1).
Source
ALDACTONE (spironolactone) tablets, for oral use, prescribing information. Pfizer. DailyMed, version published December 1, 2025. DailyMed setid 0fed2822-3a03-4b64-9857-c682fcd462bc
No. The current Aldactone label has no boxed warning.
These are the label's own numbers from the Adverse Reactions section. Where the label compares with placebo (a dummy treatment), both columns are shown, so you can see how much more often a reaction happened on Aldactone.
| Body system | Reactions the label lists |
|---|---|
| Digestive | Gastric bleeding, ulceration, gastritis, diarrhea and cramping, nausea, vomiting |
| Reproductive | Decreased libido, inability to achieve or maintain erection, irregular menses or amenorrhea, postmenopausal bleeding, breast and nipple pain |
| Hematologic | Leukopenia (including agranulocytosis), thrombocytopenia |
| Hypersensitivity | Fever, urticaria, maculopapular or erythematous cutaneous eruptions, anaphylactic reactions, vasculitis |
| Metabolism | Hyperkalemia, electrolyte disturbances, hyponatremia, hypovolemia |
| Musculoskeletal | Leg cramps |
| Nervous system/psychiatric | Lethargy, mental confusion, ataxia, dizziness, headache, drowsiness |
| Liver/biliary | A very few cases of mixed cholestatic/hepatocellular toxicity, with one reported fatality |
| Renal | Renal dysfunction (including renal failure) |
| Skin | Stevens-Johnson Syndrome (SJS), toxic epidermal necrolysis (TEN), drug rash with eosinophilia and systemic symptoms (DRESS), alopecia, pruritis |
Reactions identified in clinical trials or reports after approval. The label gives no frequencies for these, because they were reported voluntarily from a population of uncertain size.
In RALES, about 9% of men with heart failure on a mean dose of 26 mg once daily developed gynecomastia. The risk rises with dose, onset varies from 1 to 2 months to over a year, and it is usually reversible.
In RALES (1,663 people with severe heart failure), the mean daily dose at study end was 26 mg. People with baseline potassium above 5.0 mEq/L or creatinine above 2.5 mg/dL were excluded.
The Warnings and Precautions part of the label lists these. Each line gives the label's heading and what it means in plain words.
Who should not take it. People with high blood potassium (hyperkalemia), Addison's disease, or who take eplerenone.
High potassium. Aldactone can raise potassium. The risk is higher with kidney impairment, potassium supplements, salt substitutes, or medicines that raise potassium such as ACE inhibitors and ARBs. Potassium is checked within 1 week of starting or changing the dose and regularly after; if it is high, the dose is lowered or Aldactone is stopped.
Low blood pressure and worsening kidney function. Too much fluid loss can cause dehydration, low blood pressure and worse kidney function, especially in salt-depleted people or those on ACE inhibitors or ARBs. Fluid status and kidney function are checked periodically.
Salt and metabolic changes. Aldactone can also cause low sodium, magnesium and calcium, hypochloremic alkalosis and high blood sugar. High uric acid can occur, and rarely gout. Electrolytes, uric acid and blood sugar are checked periodically.
Breast enlargement in men. Aldactone can cause gynecomastia; the risk rises with dose and it is usually reversible.
Liver cirrhosis. In cirrhosis with ascites, sudden fluid and salt shifts may bring on worsening hepatic encephalopathy and coma, so Aldactone is started in the hospital at the lowest dose and raised slowly.
Drug interactions. Lithium levels can rise; NSAIDs and aspirin may weaken its effect; cholestyramine has caused high-potassium acidosis; it can disturb digoxin blood tests; use with abiraterone is not recommended; and use with mitotane is avoided.
Dose Track has a side-effect log. Each entry records the symptom, a severity (none, mild, moderate, severe or life-threatening), the date and an optional note, and can be tied to a specific dose or logged on its own. The history screen shows what you logged over time, which makes it easier to tell your prescriber when a reaction started and whether it is easing. The app records what you enter; it does not judge whether a symptom is serious. For anything on the label's call-your-doctor list, call your doctor.
This page is what the FDA label says, in plain words. It is not medical advice. Follow your prescriber, and ask them or your pharmacist about anything here.