Many medicines begin life with one purpose and end up proving useful for a completely different reason.
Few areas show this more clearly than men’s health. Three drugs in particular have become household names not because of their original uses, but because of what researchers later discovered they could do.
Their stories show how scientific serendipity, careful observation and patient experience can reshape modern medicine.
Sildenafil
Sildenafil is perhaps the most famous example of drug repurposing in modern medicine.
In the early 1990s, scientists were testing it as a treatment for angina, a type of chest pain caused by reduced blood flow to the heart. Sildenafil works by blocking the enzyme phosphodiesterase type 5 (PDE5), thereby relaxing blood vessels and, in theory, improving circulation.
Although it was largely ineffective for angina, trial volunteers kept reporting a different effect: persistent erections.
Researchers quickly realised that sildenafil improved blood flow not just to the heart, but also to the penis. This helps achieve and maintain an erection when sexually stimulated.
This discovery led to the development of the first oral treatment for erectile dysfunction, launched in 1998 and branded as Viagra. Sildenafil helped reduce the stigma around discussing male sexual health.
Today, sildenafil is also used for pulmonary hypertension, a rare condition involving high blood pressure in the lungs. This second repurposing shows how a single mechanism (widening blood vessels) can have multiple medical benefits.
Side-effects from sildenafil are usually mild and can include headaches, face flushing and nasal congestion. Sildenafil can interact with certain heart medications, such as nitrates, so medical advice is essential before using it.
Finasteride
Finasteride was initially developed in the 1980s to treat benign prostatic hyperplasia (BPH), a condition where the prostate gland becomes enlarged and causes urinary symptoms.
The drug works by blocking an enzyme called 5 alpha reductase, which converts testosterone into a more potent hormone (dihydrotestosterone) that drives prostate growth. By lowering dihydrotestosterone, the prostate in men with BPH shrinks – thus alleviating symptoms.
But during clinical trials, researchers noticed something unexpected. Men taking finasteride began reporting reduced hair loss. And, in some cases, new hair growth.
Recognising its potential, researchers tested finasteride specifically for androgenetic alopecia(male pattern hair loss). This led to a lower dose version being approved in the late 1990s for the condition, which is linked to the same hormone pathway as BPH. Blocking DHT prevents it from shrinking hair follicles, allowing weakened follicles to recover and grow thicker, longer hair.
Finasteride is now used for hair loss worldwide. Although it’s generally well tolerated, there can be uncommon side-effects, such as reduced libido or erectile difficulties. Some people also report psychiatric side-effects, such as depression and suicidal thoughts.
Finasteride’s journey shows how a drug targeting one hormone-driven condition can unexpectedly help another. It also illustrates how closely connected different aspects of men’s health can be.
Minoxidil
Another drug which has been repurposed for hair loss is minoxidil.
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Minoxidil began life in the 1960s as a treatment for severely high blood pressure. It works by relaxing and widening blood vessels, helping blood flow more easily. But researchers soon noticed something unusual: patients taking it often developed increased hair growth, sometimes in unexpected places.
This side-effect sparked interest in whether minoxidil could help with male pattern hair loss. So researchers developed a topical version (a liquid or foam applied directly to the scalp), which was approved in the 1980s.
Minoxidil works in multiple ways. An enzyme in the scalp (sulfotransferase) converts minoxidil into minoxidil sulfate, the active form of the drug. People naturally have different levels of this enzyme, which helps explain why minoxidil works well for some but less effectively for others.
Minoxidil is thought to increase blood flow to hair follicles as well, so they receive more oxygen and nutrients – creating a healthier environment for growth.
Minoxidil also affects the hair cycle. It shortens the telogen (resting) phase in hair follicles, which means these resting follicles move more quickly into growth mode. It also extends the anagen (active growth) phase, so hairs grow for longer and become thicker.
Because telogen is shortened, some people notice increased shedding in the first few weeks. This is temporary and usually means older hairs are making way for new growth. Research suggests minoxidil also supports follicle health in other ways.
It’s now widely used by men of all ages, often as a first-line treatment for thinning hair. Minoxidil is also effective for many women with female pattern hair loss and was licensed in the 1990s.
Side-effects are usually limited to scalp irritation or dryness. Because it works locally, it avoids the whole-body effects associated with finasteride.
Health advances
Repurposing medicines is not just about convenience. It can make treatments faster to develop, cheaper and safer, because the drugs have already been tested in humans. For men’s health, an area where stigma can delay diagnosis and treatment, repurposed drugs have played a particularly important role.
These repurposed drugs’ stories also remind us that medical progress is not always linear. Sometimes breakthroughs come from unexpected places: a trial side-effect, a curious researcher or a patient who notices something new.
The next major advance in health might already be sitting on a pharmacy shelf, waiting for someone to look at it differently.
