3 men’s health blockbuster drugs that started as clinical surprises

By MDLinx staffFact-checked by Davi ShermanPublished July 13, 2026

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Minoxidil shedding is a temporary increase in hair fall that happens when you first start the medication. It’s actually a sign that it’s working—older hairs are being pushed out to make room for new, thicker ones.

—Hannah Kopelman, DO, via Hims

Sometimes the biggest advances in medicine don’t come from a brilliant new hypothesis—they come from a side effect nobody expected.

Drug repurposing has shaped modern medicine for decades, but few specialties illustrate this better than men’s health.

Three of the most commonly prescribed medications in primary care—sildenafil, finasteride, and minoxidil—weren’t originally designed for erectile dysfunction or hair loss at all. Instead, they became blockbusters because clinicians noticed something unexpected during clinical trials.

For physicians, these stories offer reminders that careful observation, patient-reported outcomes, and a willingness to rethink assumptions can completely change the trajectory of a drug—and sometimes an entire field of medicine.

The heart drug that changed sexual health care

Perhaps no drug better exemplifies successful repurposing than sildenafil. ^[]

In the early 1990s, researchers were investigating sildenafil as a treatment for angina. Because the drug inhibits phosphodiesterase type 5 (PDE5), investigators hoped its vasodilatory effects would improve coronary blood flow and relieve ischemic chest pain.

The cardiovascular results, however, were underwhelming. Patients enrolled in clinical trials consistently reported an entirely different effect: improved erections.

Rather than dismissing those reports as an inconvenient side effect, investigators recognized a new therapeutic opportunity. Increased penile blood flow through PDE5 inhibition ultimately led to sildenafil becoming the first oral medication approved for erectile dysfunction in 1998, fundamentally changing how physicians approached sexual medicine.

Today, sildenafil has found yet another indication. Its vasodilatory effects also make it an effective treatment for pulmonary arterial hypertension, demonstrating how a single pharmacologic mechanism can have multiple clinically valuable applications.

For clinicians, the familiar counseling points remain important. Common adverse effects include headache, flushing, and indigestion, while concomitant nitrate therapy remains a major contraindication because of the risk of profound hypotension.

A prostate drug that became a hair loss therapy

Finasteride followed a similarly unexpected path. The drug was initially developed to treat benign prostatic hyperplasia (BPH). By inhibiting 5-alpha reductase, finasteride decreases conversion of testosterone to dihydrotestosterone (DHT), reducing prostatic enlargement and improving lower urinary tract symptoms. ^[]

Then clinicians noticed an intriguing trend. Patients weren’t simply experiencing improved urinary symptoms—they were also reporting reduced hair loss and, in many cases, new hair growth.

That observation prompted investigators to evaluate lower-dose finasteride specifically for androgenetic alopecia. Because DHT also drives miniaturization of scalp hair follicles, the same biologic pathway responsible for shrinking the prostate also slowed male pattern baldness. Today, finasteride is widely prescribed for both conditions, albeit at different doses.

As physicians know, patient counseling extends beyond efficacy. Although most men tolerate therapy well, discussions should include potential adverse effects. Shared decision-making remains essential when initiating long-term therapy.

A blood pressure medication that grows hair

Minoxidil’s transformation may be the most obvious example of serendipity. Originally introduced as an oral antihypertensive in the 1970s, minoxidil acts as a potent vasodilator for patients with severe hypertension. ^[]

During treatment, however, clinicians noticed an unusual adverse effect: excessive hair growth. Researchers soon realized this side effect could become the drug’s primary therapeutic purpose. A topical formulation was subsequently developed and approved for androgenetic alopecia, where it remains one of the first-line treatments decades later.

Although its precise mechanism isn’t completely understood, topical minoxidil appears to improve follicular blood flow, prolong the anagen phase of the hair cycle, shorten the telogen phase, and support healthier follicle function. Variability in scalp sulfotransferase activity likely explains why some patients respond dramatically while others experience minimal benefit.

Patients should also be prepared for one of the treatment’s more misunderstood effects: a temporary increase in shedding during the first several weeks. ^[]

“Minoxidil shedding is a temporary increase in hair fall that happens when you first start the medication. It’s actually a sign that it’s working—older hairs are being pushed out to make room for new, thicker ones,” Hannah Kopelman, DO, told Hims.

Clinical takeaways

These stories highlight an important lesson that extends far beyond men’s health.

Some of medicine’s most impactful therapies weren’t born from perfectly executed research plans. They emerged because investigators paid attention to unexpected findings instead of dismissing them.

Drug repurposing offers several advantages:

Development timelines are shorter because much of the safety data already exist.
Costs are substantially lower than developing entirely new compounds.
Clinicians gain additional treatment options by leveraging well-understood pharmacology.
Careful attention to patient-reported outcomes can uncover therapeutic opportunities that traditional endpoints may miss.

For practicing physicians, these medications also serve as reminders that adverse effects aren’t always simply adverse. Occasionally, they’re clues pointing toward an entirely new indication.

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