The History of Finasteride: From Prostate Medication to Hair Loss Treatment

Finasteride wasn’t always a bathroom cabinet staple. Twenty years ago, if you walked into a pharmacy asking for it, the pharmacist would’ve assumed you were treating an enlarged prostate - not thinning hair. The story of how this drug went from helping men urinate more easily to helping them keep their hair is a perfect example of medical serendipity. It’s not just a tale of accidental discovery. It’s a story of science, patience, and a little bit of luck that changed millions of lives.

How Finasteride Was Born in a Lab

Finasteride was developed in the late 1980s by Merck & Co., a pharmaceutical giant based in New Jersey. The goal? To find a drug that could shrink an enlarged prostate. Benign prostatic hyperplasia (BPH) was - and still is - a common issue for men over 50. The prostate gland swells, presses on the urethra, and makes urination painful or difficult. Doctors needed a better solution than surgery or bulky medications with harsh side effects.

Researchers knew that testosterone played a role in prostate growth. But they didn’t just target testosterone. They targeted its conversion into a stronger hormone: dihydrotestosterone, or DHT. DHT is what actually makes the prostate grow. The enzyme that turns testosterone into DHT is called 5-alpha reductase. So Merck’s team set out to block it.

After years of testing hundreds of compounds, they found finasteride. It was selective. It blocked type 2 5-alpha reductase - the version mostly found in the prostate and scalp - without messing with type 1, which is found in the skin and liver. That precision made it safer than earlier drugs. In 1992, the FDA approved finasteride under the brand name Proscar for treating BPH. Dose? 5 milligrams daily.

The Unexpected Side Effect That Changed Everything

When Proscar hit the market, doctors started noticing something odd. Men taking it for their prostate weren’t just urinating better. Some were also growing hair back.

It wasn’t a fluke. In clinical trials, researchers recorded hair growth as a side effect - but they didn’t chase it. Why? Because the dose was five times higher than what would be needed for hair loss. And at that dose, side effects like reduced libido and erectile dysfunction were common. No one thought it was worth pursuing.

Then, in 1995, a dermatologist named Dr. John R. McElwee started asking questions. He had seen patients with male pattern baldness who were also taking finasteride for prostate issues. He noticed their hairlines were improving. He dug into the data and found a pattern: men on finasteride were losing less hair - and in some cases, regrowing it.

Merck took notice. They ran a new trial. This time, they lowered the dose to 1 milligram. They focused only on men with mild to moderate hair loss. The results? After one year, 83% of men taking finasteride stopped losing hair. Nearly 66% saw noticeable regrowth. By 1997, the FDA approved the lower-dose version under the brand name Propecia.

The same molecule. Half the dose. A completely new use.

Why Finasteride Works for Hair Loss

Male pattern baldness isn’t just about aging. It’s genetic. Men with this condition have hair follicles that are sensitive to DHT. Over time, DHT shrinks the follicles. Hair grows thinner, shorter, until it stops growing at all. The follicles don’t die - they just go dormant.

Finasteride works by cutting off the DHT supply. By blocking 5-alpha reductase, it reduces DHT levels in the scalp by up to 70%. That gives the follicles a chance to recover. Hair that was barely hanging on starts growing thicker. New hairs appear in thinning areas - especially on the crown and hairline.

But here’s the catch: it only works as long as you take it. If you stop, DHT levels rise again. The follicles shrink back. Hair loss resumes within 6 to 12 months. That’s why finasteride isn’t a cure. It’s a maintenance drug.

Who Benefits the Most - and Who Doesn’t

Not everyone responds the same way. Finasteride works best for men with early-stage hair loss - thinning at the temples or crown. It’s less effective for those who’ve been bald for more than five years. The follicles are too far gone.

Studies show that men under 40 see the strongest results. The younger the hair loss, the better the chance of regrowth. Men over 50 still benefit, but mostly in slowing further loss. Regrowth is slower and less dramatic.

Women don’t use finasteride for hair loss. It’s not approved for them. In fact, it can cause birth defects if taken during pregnancy. Even touching crushed pills can be risky for pregnant women. That’s why pharmacies keep it behind the counter.

And while it’s effective for male pattern baldness, it doesn’t help with other types of hair loss - like alopecia areata, thyroid-related shedding, or stress-induced shedding. It only targets DHT-related thinning.

The Side Effects Nobody Talks About

Most men tolerate finasteride well. But a small percentage - about 1 to 2% - report persistent side effects. These include low libido, trouble getting or keeping an erection, and reduced semen volume. These usually go away when you stop taking the drug.

But some men say the side effects linger - even after stopping. This is called Post-Finasteride Syndrome (PFS). It’s controversial. The FDA doesn’t recognize it as a formal diagnosis. Major medical societies say evidence is limited. But thousands of men have shared their stories online. Some say their sex drive, mood, and energy never fully returned.

Doctors are divided. Some dismiss it as psychological. Others say the biological mechanism isn’t fully understood. What’s clear: if you’re considering finasteride, talk to your doctor. Know the risks. Track your symptoms. And don’t ignore changes that stick around.

Finasteride Today: Generic, Accessible, and Controversial

Propecia’s patent expired in 2013. Today, you can buy generic finasteride for less than $10 a month in the U.S. In the UK, it’s available on the NHS for prostate issues - but not for hair loss. That means men seeking it for thinning hair must pay out of pocket.

Online pharmacies and telehealth clinics have made it easier than ever to get. But that also means people are self-prescribing. Some skip doctor visits. Some don’t know if their hair loss is even DHT-related. That’s dangerous. Hair loss can signal thyroid problems, iron deficiency, or even heart disease.

Finasteride is now one of the most prescribed drugs for hair loss worldwide. But it’s also one of the most debated. On one side: men who got their confidence back. On the other: men who lost more than just hair.

What Comes Next?

Scientists are already looking beyond finasteride. New drugs like dutasteride (which blocks both types of 5-alpha reductase) are being studied for hair loss. Topical versions of finasteride - applied directly to the scalp - are in trials. They aim to reduce systemic side effects.

Stem cell therapies, platelet-rich plasma (PRP), and low-level laser treatments are also gaining traction. But none have the 25+ years of real-world data that finasteride has.

For now, finasteride remains the gold standard. Not because it’s perfect. But because it works - for millions - and we know how it behaves over time.

It started as a prostate drug. It became a hair loss treatment. And now, it’s a symbol of how medicine can surprise us - sometimes in ways we never expected.