Spironolactone’s most common side effects include dizziness, fatigue, muscle cramps, nausea, and breast tenderness or enlargement. These occur in more than 1 in 100 people who take the drug. Because spironolactone is a potassium-sparing diuretic that also blocks certain hormones, its side effects fall into a few distinct categories: those related to fluid loss, those related to potassium buildup, and those caused by hormonal changes.
Everyday Side Effects Most People Notice
The side effects you’re most likely to experience are the ones tied to how spironolactone removes excess fluid from your body. Feeling dizzy, especially when standing up quickly, is one of the earliest and most common. This happens because the drug lowers your blood volume, which can temporarily drop your blood pressure when you change positions. For most people, this improves after the first few days. Getting up slowly from sitting or lying down helps considerably.
Fatigue and low energy are also frequent, particularly in the first weeks. Nausea and muscle or leg cramps round out the list of common complaints. The cramps can be related to shifts in your electrolyte balance as your kidneys adjust to the medication.
Hormonal Side Effects
Spironolactone doesn’t just act on the receptors that regulate salt and water balance. It also blocks androgen receptors, which is why it’s widely prescribed off-label for hormonal acne and hair loss in women. But that same androgen-blocking activity is responsible for some of its most distinctive side effects.
In women, menstrual irregularities are common. You may notice irregular periods, breakthrough bleeding, or spotting between cycles. Breast tenderness and breast enlargement can also occur. These effects are more pronounced at higher doses and often improve over time, though they don’t always resolve completely.
In men, the androgen-blocking effect can cause breast tissue growth (gynecomastia) and breast pain. This was one of the side effects that historically limited spironolactone’s use, particularly at higher doses prescribed for heart failure. Some men also experience reduced sex drive.
High Potassium: The Risk to Take Seriously
Unlike most diuretics, which flush potassium out of your body, spironolactone causes your kidneys to hold onto it. This means potassium levels can climb too high, a condition called hyperkalemia. In the landmark RALES heart failure trial, serious hyperkalemia occurred in about 2% of patients on spironolactone compared to 1% on placebo. That’s a relatively low rate, but the consequences of very high potassium (muscle weakness, abnormal heart rhythms, and in extreme cases cardiac arrest) make it the most medically significant side effect of this drug.
Your risk is higher if you have kidney problems, are older, take other medications that raise potassium (like ACE inhibitors or certain blood pressure drugs), or use potassium supplements. Doctors typically check your potassium levels with a blood test before starting spironolactone and again within the first few weeks, then periodically after that.
Foods and Supplements That Affect Potassium
While you don’t need to avoid potassium-containing foods entirely, being aware of your intake matters. Potassium supplements are the biggest concern and should generally be avoided unless your doctor specifically prescribes them alongside spironolactone. Salt substitutes are another common culprit, since many brands replace sodium chloride with potassium chloride. Combining these with spironolactone can push your levels into a dangerous range.
Interestingly, licorice (real licorice, not the candy flavored with anise) interacts with spironolactone in the opposite direction. Licorice and licorice extract can actually make the drug less effective, so most doctors recommend avoiding them during treatment.
How Dose Affects Side Effects
Spironolactone is prescribed across a wide range of doses. Someone taking 25 mg daily for mild fluid retention will generally experience fewer and milder side effects than someone on 100 to 200 mg for heart failure or resistant high blood pressure. The hormonal side effects in particular, like breast changes and menstrual irregularities, tend to become more noticeable as the dose increases.
For acne treatment, doses typically fall in the 50 to 100 mg range. At these levels, the hormonal side effects are present but often manageable. Many women find that irregular periods are the most bothersome issue and that it stabilizes after a few months on a consistent dose.
Effects on Blood Pressure and Hydration
Because spironolactone is a diuretic, it increases urination, especially in the first days of treatment or after a dose increase. This fluid loss is the whole point when the drug is prescribed for conditions like heart failure or high blood pressure, but it can also leave you feeling dehydrated or lightheaded if you’re not drinking enough water.
Drops in blood pressure upon standing (orthostatic hypotension) become more likely if you’re also taking other blood pressure medications, are on a higher dose, or are over 70. The general threshold doctors watch for is a systolic blood pressure drop of 20 points or more within three minutes of standing. If you’re consistently feeling faint when you get up, that’s worth mentioning at your next appointment rather than pushing through it.
What Usually Improves and What Doesn’t
Many of the fluid-related side effects, like dizziness, frequent urination, and fatigue, tend to ease within the first one to two weeks as your body adjusts. Nausea and muscle cramps often follow the same pattern.
Hormonal side effects are less predictable. Menstrual irregularities may settle into a new pattern after two to three months, or they may persist for the duration of treatment. Breast tenderness in both men and women sometimes improves but can be an ongoing issue, particularly at higher doses. If a side effect is significantly affecting your quality of life, a dose adjustment is often the first thing to try, since many of these effects are clearly dose-dependent.