How it works
Sildenafil inhibits phosphodiesterase type 5 (PDE5), preventing breakdown of cGMP in penile smooth muscle. Sexual arousal triggers nitric oxide release; cGMP then accumulates, smooth muscle relaxes, and blood flow increases.
The evidence
Multiple Phase III trials demonstrated efficacy in 70–80% of men with ED across etiologies. Long-term safety established over 25+ years of use.
Typical dosing
25, 50, or 100 mg taken 30–60 minutes before sexual activity, on an empty stomach for best onset. Maximum once per 24 hours.
Side effects
Common
- Headache
- Flushing
- Nasal congestion
- Indigestion
Less common
- Visual disturbance (blue tinge)
- Back pain
Rare
- Priapism (> 4 hr erection — medical emergency)
- Sudden hearing or vision loss
Drug interactions
- Nitrates — absolute contraindication (severe hypotension)
- Alpha-blockers — hypotension risk
- CYP3A4 inhibitors (e.g. ketoconazole) — reduce sildenafil dose