How it works
Sildenafil blocks an enzyme called phosphodiesterase type 5 (PDE5). PDE5 breaks down cGMP, a chemical in the smooth muscle of the penis. When you're aroused, your body releases nitric oxide. With PDE5 blocked, cGMP builds up. The muscle relaxes, and more blood flows in.
The evidence
Large trials showed it helped many men with ED, whatever the cause. Its long-term safety is well known from 25+ years of use.
Typical dosing
25, 50, or 100 mg, taken 30–60 minutes before sex. It starts working best on an empty stomach. Take it no more than once every 24 hours.
Side effects
Common
- Headache
- Flushing
- Stuffy nose
- Indigestion
Less common
- Vision changes (a blue tint)
- Back pain
Rare
- Priapism (an erection lasting over 4 hours; a medical emergency)
- Sudden hearing or vision loss (get care right away)
Drug interactions
- Nitrates, including "poppers": never take them together (blood pressure can drop dangerously)
- Riociguat (for lung blood pressure): never take them together
- Alpha-blockers: risk of low blood pressure
- CYP3A4 inhibitors (like ketoconazole): use a lower sildenafil dose
