Spironolactone Side Effects: What to Expect and When to Call Your Doctor

Spironolactone is generally well-tolerated, but like all medications, it comes with a range of potential side effects — from minor inconveniences to rare but serious problems. Understanding what to watch for helps you stay safe and know when you need to call your doctor. This guide covers the full picture of spironolactone side effects in plain English.

The Most Important Side Effect to Know: Hyperkalemia (High Potassium)

Spironolactone blocks aldosterone, which normally causes the body to excrete potassium. When you block aldosterone, potassium levels in your blood can rise. This is called hyperkalemia, and at high levels, it can be life-threatening because it affects heart rhythm.

Symptoms of dangerous hyperkalemia include:

Nausea, weakness, or fatigue

Tingling or numbness in hands, feet, or lips

Irregular or slow heartbeat (palpitations)

Chest pain or pressure

Muscle weakness or paralysis (in severe cases)

Call 911 or go to the ER immediately if you experience chest pain, severe muscle weakness, or an irregular heartbeat while taking spironolactone.

Your doctor will regularly check your potassium level (via a blood test) while you're on spironolactone — especially when starting, increasing the dose, or if you develop kidney problems. Avoid potassium supplements and salt substitutes containing potassium (like NoSalt or Nu-Salt) unless your doctor specifically instructs otherwise.

Common Side Effects (Most Patients Tolerate These)

These side effects are relatively common and, while bothersome, are usually not dangerous:

Dizziness or lightheadedness: Especially when standing up quickly (orthostatic hypotension). Get up slowly from sitting or lying positions.

Frequent urination: Spironolactone is a diuretic — increased urination is expected. Taking your dose in the morning (rather than evening) can help prevent nighttime trips to the bathroom.

Nausea, stomach cramps, or diarrhea: GI side effects can be reduced by taking spironolactone with food. Most resolve within a few weeks of starting.

Headache: Common early in treatment. Usually improves as your body adjusts.

Drowsiness or fatigue: Some patients feel tired or mentally foggy, especially at higher doses.

Hormonal Side Effects: Important Differences Between Men and Women

Because spironolactone blocks androgen receptors in addition to aldosterone receptors, it has sex hormone-related side effects that differ significantly between men and women.

In Men:

Gynecomastia (breast tissue growth): One of the most common reasons men stop spironolactone. It occurs in roughly 9% of men at lower doses and increases at higher doses. Usually resolves after stopping the medication if caught early.

Loss of libido (sex drive): Reduced testosterone-related effects may decrease sexual interest. Generally dose-dependent.

Erectile dysfunction: Possible at higher doses. Discuss with your doctor if this is a concern; switching to eplerenone may help.

In Women:

Menstrual irregularities: Including irregular periods, lighter or heavier periods, or absent periods (amenorrhea). Occurs in 10-50% of women at moderate doses and nearly all women at high doses (200 mg/day). Taking spironolactone with a combined oral contraceptive can help regulate cycles.

Breast tenderness: Some women experience breast soreness, particularly early in treatment.

Spotting between periods: Breakthrough bleeding (metrorrhagia) can occur, especially in the first few months.

Serious Side Effects That Require Medical Attention

Hyperkalemia (high potassium): As described above. Symptoms: weakness, irregular heartbeat, tingling, chest pain. Seek emergency care.

Kidney function worsening: Symptoms: decreased urination, swelling in legs/feet, fatigue. Contact your doctor promptly if you notice these.

Severe allergic reaction: Rare but possible. Symptoms: hives, difficulty breathing, swelling of face/lips/tongue/throat. Call 911.

Severe dehydration or hyponatremia (low sodium): Symptoms: confusion, extreme thirst, vomiting, muscle cramps. Contact your doctor.

The Boxed Warning: Tumorigenicity

Spironolactone carries an FDA boxed warning about tumorigenicity — it caused tumors in animals given high doses over long periods. However, there is no established evidence that spironolactone causes tumors in humans at the doses used clinically. The FDA's guidance is to avoid unnecessary use, meaning it should only be prescribed for conditions that genuinely benefit from it.

Tips for Managing Side Effects

Take with food to reduce nausea and stomach upset.

Take in the morning to prevent nighttime urination.

Avoid high-potassium foods (bananas, oranges, potatoes) in large quantities if your potassium tends to run high.

Report side effects to your doctor early — dose adjustments can often resolve them without needing to stop the medication entirely.

Also read our guide on spironolactone drug interactions — many of the most serious side effects are worsened by specific drug combinations.