Spironolactone vs Finasteride for Female Hair Loss

June 13, 2025/Andrew Le

Spironolactone blocks aldosterone, pushing out extra salt and water, while finasteride cuts down DHT, a powerful hormone that drives hair loss. As a result, they help with problems like swelling, high blood pressure, or hair thinning.

But which one works better? Or which one has fewer side effects?

In this article, we’ll break down how each drug works, how well they perform, and what side effects you should know before starting treatment.

🔑 Key Takeaways

➤ Spironolactone helps your kidneys flush out extra salt and water to lower blood pressure, while finasteride works in tissues to block DHT and slow hair loss.

➤ Spironolactone targets the hormone aldosterone in your kidneys, but finasteride targets the enzyme that turns testosterone into DHT in your scalp.

➤ Spironolactone is often used to reduce swelling in heart or liver problems, whereas finasteride is mainly used to treat hair thinning.

➤ Women can see steady hair improvement with low-dose spironolactone over months, but finasteride usually needs higher doses or longer treatment for clear benefits.

➤ High doses of spironolactone can cause irregular bleeding, while finasteride may cause mild side effects like headache or low libido that tend to fade over time.

➤ If you stop spironolactone, fluid levels can build up again, and if you stop finasteride, DHT levels return to normal in about two weeks.

➤ Spironolactone keeps potassium levels stable while flushing out sodium, but finasteride does not affect your body’s salt balance.

Mechanism of Action

Spironolactone works by blocking aldosterone to remove extra salt and water, while finasteride works by lowering DHT to slow hair loss.

How Does Spironolactone Work?

According to Pfizer’s clinical pharmacology data, spironolactone works as a specific antagonist of aldosterone. It acts by competing for receptor sites at the aldosterone-dependent sodium-potassium exchange in the distal convoluted renal tubule. This action leads to more sodium and water being flushed out through urine, while potassium is kept inside the body. This balance helps spironolactone act as both a diuretic (which helps the body get rid of extra fluid) and an antihypertensive drug (which lowers blood pressure). 

Importantly, spironolactone also directly targets conditions like hyperaldosteronism (where there’s too much aldosterone in the body) by blocking aldosterone’s effects. 

By doing so, it helps reduce swelling and fluid buildup in conditions like heart failure, liver cirrhosis, and nephrotic syndrome. 

How Does Finasteride Work?

Finasteride works in a very different way. It is a competitive inhibitor of the type II and III isoenzymes of 5-alpha reductase. This enzyme normally converts testosterone into dihydrotestosterone (DHT), a more potent androgen. By blocking this conversion, finasteride drastically lowers DHT levels — research shows that it reduces serum DHT levels by 70%. 

In conditions like androgenic alopecia (male pattern hair loss), DHT plays a central role. By lowering DHT, finasteride helps slow hair loss. Interestingly, even though it cuts DHT significantly, it doesn’t bring levels to zero, meaning hair loss slows but doesn’t completely stop. And when the treatment stops, DHT levels bounce back to normal in about 14 days. 

Finasteride’s action, then, is all about reducing androgen effects in tissues. This makes it a key anti-androgenic agent for several conditions, including off-label uses like treating hirsutism or supporting hormone therapy in transgender women.

Efficacy

Spironolactone has been shown to help many women with hair loss by blocking androgens, working well even at low doses and over long periods.

On the other hand, finasteride only shows clear hair growth benefits at higher doses, with mixed results depending on a woman’s age, hormone levels, and how long she takes it.

Spironolactone for Female Hair Loss

One open-intervention study showed that using high-dose spironolactone, at 200 mg daily, worked just as well as cyproterone acetate, a strong androgen blocker, for treating female pattern hair loss (FPHL). That’s impressive because cyproterone acetate is a well-known treatment. 

It suggests that spironolactone, even at high doses, has the power to block the effects of androgens that can harm hair follicles. Interestingly, in another study, combining low-dose oral minoxidil with spironolactone at 25 mg daily helped stimulate hair growth. This points to a benefit when using spironolactone together with other treatments, even at lower doses.

Moving forward, one retrospective observational study of 79 women aged 21 to 79 years with FPHL, using spironolactone at an average dose of 100 mg daily (ranging from 25 to 200 mg) for at least six months found that after treatment, all patients either kept or improved their Sinclair score, with an average increase of 0.65 points. Interestingly, the degree of improvement matched how severe the hair loss was at the start. About 64% of women who used spironolactone for over a year showed their best scores after one year or more. Even more promising, this improvement didn’t depend on other treatments, menopause status, or hormonal contraceptive use. 

This means spironolactone alone or with long-term treatments can offer steady results.

One study on low-dose spironolactone (up to 50 mg daily) in 62 women revealed encouraging results. These women, with an average age of 62, saw their Sinclair scores drop from 2.47 to 1.81 after about one year. Even when removing patients who used other treatments like minoxidil or platelet-rich plasma, the improvement held, going from 2.63 to 1.95. 

What does this tell us? Low-dose spironolactone may still be effective, especially for those who can’t handle higher doses or have a higher risk of side effects. Adverse events were mild, such as lightheadedness or mild hyperkalemia, and none of the patients had to stop treatment because of them. This makes low-dose spironolactone a valuable option for many women.

Finasteride for Female Hair Loss

A large randomized controlled trial with 137 postmenopausal women taking 1 mg of finasteride daily for one year showed no significant improvement in hair loss compared to placebo. Both groups even experienced a slight drop in hair count, with the finasteride group losing about 8.7 hairs and the placebo group about 6.6 hairs. Patient and doctor assessments also found no noticeable change in hair appearance or growth. 

Likewise, one study tested 1.25 mg of finasteride daily in 18 women over seven months, showing only a small 5.9% increase in hair density and 11.8% increase in thickness, but just 14% of the patients actually reported seeing any improvement. This suggests that low-dose finasteride may not offer much help for most women with female pattern hair loss (FPHL), especially postmenopausal women, even though it reduces hormone levels like DHT in the body.

In contrast, several studies found better results with medium or high doses. One study explored five postmenopausal women taking 2.5 to 5 mg of finasteride daily for 18 months. All of them saw their hair loss stop, and four reported visible hair growth. 

Similarly, one study followed 37 premenopausal women taking 2.5 mg finasteride with an oral contraceptive for a year. About 62% showed improved hair density, and nearly 78% felt their hair was better overall. Even stronger effects came from another research study that tested 5 mg daily in 87 women for 12 months, finding an 18.9% rise in hair density and 9.4% increase in hair diameter, with over 80% of women noticing improvements. Together, these studies suggest that higher doses of finasteride might work better for women with FPHL, though responses can differ by age and hormone status.

Looking at longer-term studies, one study ran a three-year retrospective study with 120 women using either 1.25 mg finasteride or 0.15 mg dutasteride daily. Around 82% of those on finasteride showed better hair thickness, and nearly 69% had improved scalp coverage, suggesting that even lower doses might help when used over a long time. However, another study of 48 premenopausal women with high androgen levels found that 5 mg finasteride was less effective than other treatments, like flutamide, in reducing hair loss. This means that while finasteride can be effective, especially at higher doses and longer durations, it may not work equally well for every woman, depending on hormone levels or underlying conditions. 

Side Effects

Spironolactone can cause bothersome side effects like unexpected bleeding, especially at high doses, making it hard for some women to keep using, while finasteride’s side effects—like low libido or headaches—are usually mild and tend to fade over time, so most women keep taking it if they see hair improvement.

Side Effects of Spironolactone

A study on 26 premenopausal women with idiopathic hirsutism revealed notable side effects when using spironolactone. 

Sixteen women were first given 100 mg twice daily during days 4–21 of their menstrual cycle. Strikingly, 68% (11 women) had to either lower the dose or stop the medication because of side effects. 

What was the most common issue? Irregular menstrual bleeding, or unexpected vaginal bleeding with 14-day cycles, affected 56% (9 women). While this bleeding was not dangerous, it was bothersome enough for many women to stop treatment. 

On top of that, one woman experienced urticaria (hives), and another reported scalp hair loss. When a lower dose was used — 50 mg twice daily — only 2 out of 10 women developed metrorrhagia, and no other side effects were noted.

This shows that higher doses of spironolactone increase the risk of bleeding problems, making the medication hard to tolerate for some women. It also suggests that starting with lower doses or combining spironolactone with estrogen/progesterone might help reduce these side effects.

While effective, spironolactone can bring challenging side effects, especially at higher doses.

Side Effects of Finasteride

One study of 256 premenopausal women with female pattern hair loss (FPHL) explored the side effects of taking 5 mg/day of finasteride. After just 3 months, about 1 in 5 patients (roughly 20%) reported at least one side effect. 

These effects mostly faded over time, even when the medication was continued. At the 36-month mark, only 1 in 30 patients (about 3%) still had any complaints. 

What were these side effects? Seven women reported decreased libido, one woman experienced hypertrichosis (increased body hair), and one woman had mastalgia (breast pain).

Other reported side effects in similar studies included:

  • Headache (seen in 10–25% of women)
  • Menstrual irregularities
  • Dizziness
  • Gastrointestinal discomfort
  • Dry skin
  • Mild acne

Importantly, even though some women had these issues, most chose to keep taking finasteride because they felt it was working well.

This means that although finasteride can cause mild and temporary side effects, they usually lessen with time. For many women, the benefits of improved hair loss outweigh these early side effects. 

⚠️ Important Considerations

It’s important to remember that finasteride is not approved for use in pregnant women because it can cause abnormalities in male fetuses. So, careful planning and medical guidance are crucial when using this medication.

Wrap Up

Spironolactone works in the kidneys to wash out extra salt and water, so it eases swelling and lowers blood pressure. In contrast, finasteride works in tissues to cut DHT, slowing hair loss. Both drugs have strengths and side effects. Spironolactone may cause irregular menstrual bleeding at high doses, while finasteride can bring mild, short-lived effects like low libido or headaches. However, stopping either drug reverses its benefits. Ultimately, deciding between them depends on the problem you face and how you handle side effects.

Careful planning with a doctor will guide you to the right choice. Which factors matter most? Think about your goals, risks, and how each medicine fits your life.

Frequently Asked Questions

Do I need a prescription for these medications?

Yes, both spironolactone and finasteride need a prescription. They’re not sold over-the-counter.

Is hair loss treatment a one-time fix?

No, these treatments need to be used long-term. If you stop, hair loss can come back.

Does spironolactone help with anything besides hair loss?

Yes! It’s also used to treat acne and excess facial hair (hirsutism) in women.

Sources

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