In the early 1990s, a team of Pfizer scientists in Sandwich, England, was developing a drug called UK-92480 for angina — the chest pain caused by reduced blood flow to the heart. The clinical trials were disappointing. The drug wasn't doing much for chest pain.
But something unusual was happening. Male trial participants were refusing to return their unused pills.
The Accidental Discovery
The side effect was unmistakable: participants were getting erections. Not as a fluke — consistently, reliably, and with enthusiasm.
Pfizer had been looking for a heart drug. Instead, they had stumbled onto the most famous pharmaceutical pivot in history. The compound was renamed sildenafil citrate, rebranded as Viagra, and redirected toward erectile dysfunction.
On March 27, 1998, the FDA approved Viagra for the treatment of ED. It became the fastest-selling drug launch in pharmaceutical history at the time, surpassing $1 billion in global sales within its second year.
The Science of the "Accident"
Sildenafil works by inhibiting phosphodiesterase type 5 (PDE5), an enzyme that breaks down a molecule called cyclic GMP. When cyclic GMP accumulates in the smooth muscle of penile arteries, those muscles relax, blood flows in, and an erection occurs.
The same mechanism should theoretically dilate coronary arteries too. And it does — just not enough to meaningfully treat angina. But the penile arteries are far smaller and more responsive to the effect, making the erection response dramatic while the cardiac benefit was modest.
The irony: Viagra literally is a heart drug. It just turned out to work much better on a different set of arteries.
The Numbers
In its first 7 years on the market, more than 750,000 physicians prescribed sildenafil to over 23 million men. At its peak, Viagra held 92% of the global ED drug market. Even after competitors like Cialis (tadalafil) and Levitra (vardenafil) entered the space, Viagra remained the dominant brand for over a decade.
When Pfizer's patents expired — internationally in 2012 and in the US effectively by December 2017 — sales dropped sharply. By 2020, Pfizer spun off its off-patent brands (including Viagra) into a new company called Viatris.
What Changed Since Viagra
The Viagra era transformed ED from an unspoken shame into a treatable medical condition. But the original brand came with original-era pricing. At its peak, a single Viagra pill could cost $60 to $80 at a retail pharmacy.
Today, generic sildenafil is available for as little as $1 to $3 per dose through telehealth compounding pharmacies. Tadalafil (generic Cialis) offers a daily low-dose option for men who prefer an always-ready approach. And the entire consultation-to-delivery process that once required an embarrassing doctor's visit now takes 10 to 15 minutes online.
The Same Medication. A Fraction of the Price.
Generic sildenafil and tadalafil are prescribed online by licensed physicians and shipped to your door. Compare top-rated providers.
Compare Providers →The Bottom Line
Viagra's origin story is the greatest accidental discovery in pharmaceutical history. A failed heart drug became a cultural icon, generated tens of billions in revenue, and — most importantly — made millions of men realize that ED is a medical condition with a medical solution. Today, the same active ingredient is available at a tiny fraction of the original cost, and getting it doesn't require leaving your house.