Pfizer was making $1.8 billion a year on average from Viagra when the erectile dysfunction drug first appeared on the market. After the patent expired in late 2017 and competitors created cheaper alternatives and generics, Viagra sales plummeted with 73% year-over-year for 2018. Pfizer still holds the lead in the erectile dysfunction market with 65% even as Viagra sales falter. It's been able to maintain that significant share thanks in part to launching Sildenafil, its own generic version of the blue, diamond-shaped pill. Cialis and its generic, Tadalafil, and Levitra and its generic, Vardenafil, are close behind with 30% and 5% of market share, respectively.