Biggest safety “don’ts” (important)
Never combine with nitrates (like nitroglycerin/isosorbide) or “poppers” (amyl nitrite/nitrates): can cause dangerous blood pressure drops.
Do not combine with riociguat (a guanylate cyclase stimulator): also risks severe hypotension.
Do not combine with alchohol or
When to get urgent medical help
Chest pain, fainting, or severe dizziness after taking it
Erection lasting >4 hours (priapism)
Sudden vision loss or sudden hearing loss
 
Sildenafil - StatPearls - NCBI Bookshelf is a medication in a class called PDE-5 inhibitors. It works by blocking the PDE-5 enzyme, which helps increase nitric-oxide signaling and leads to relaxation of smooth muscle and widening of blood vessels (vasodilation).
 
Main medical uses
Erectile dysfunction (ED)
Helps improve erections in response to sexual stimulation by increasing blood flow to penile tissue.
Pulmonary arterial hypertension (PAH) (high blood pressure in the lung arteries)
Marketed under a different brand/dose in this setting; it helps relax pulmonary blood vessels, improve symptoms, and increase exercise capacity in appropriate patients.
 
Common “how it’s taken” basics (high level)
ED: typically taken as needed before sex, with onset often within about an hour (varies by person, dose, and whether you took it with a heavy meal).
PAH: taken on a scheduled, multiple-times-per-day regimen (not “as needed”).
(Exact dosing should come from the prescriber because it depends on age, other meds, kidney/liver function, and side effects.)
Common side effects
 
The most commonly reported include:
Headache
Flushing
Indigestion (dyspepsia)
Nasal congestion
Dizziness
Sometimes visual changes (e.g., color tinge/blurred vision)
Biggest safety “don’ts” (important)
Never combine with nitrates (like nitroglycerin/isosorbide) or “poppers” (amyl nitrite/nitrates): can cause dangerous blood pressure drops.
Do not combine with riociguat (a guanylate cyclase stimulator): also risks severe hypotension.
When to get urgent medical help
Chest pain, fainting, or severe dizziness after taking it
Erection lasting >4 hours (priapism)
Sudden vision loss or sudden hearing loss