Sildenafil (Viagra)
PDE5 inhibitor. 30-60 min onset, 4-6 hour duration. Generic available, cheap.
First PDE5 inhibitor approved (1998). Generic since 2017, very cheap ($1-3/tablet OTC outside US). 25-100mg dosing. Side effects: headache, flushing, nasal congestion, mild visual blue tint.