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 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........

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