Educational only. We do not sell medicine. Never combine an ED pill with a nitrate. Emergencies: call 911 in the United States.

MensRxGuide Sexual health and ED medication guide

Consumer guide · Label check 5 November 2026

A plain-language guide to ED medicines and the safety rules around them

MensRxGuide explains how sildenafil (Viagra), tadalafil (Cialis), vardenafil (Levitra, Staxyn), and avanafil (Stendra) differ in onset, duration, food effect, and cost pattern. It also explains the interactions that make some of those pills dangerous.

Use the reading finder Open the comparison
Prescription
These medicines are prescription-only in the United States.
Stimulation
A PDE5 inhibitor does not create an erection by itself.
This site
Does not diagnose, prescribe, or sell drugs.

Which page should you read first?

Four questions. The result is a reading path. It is not a product suggestion and it cannot clear you to take a medicine.

Comparative snapshot

Figures below are the usual adult patterns in U.S. prescribing information. A prescriber changes the dose for age, kidney or liver disease, and interacting medicines. “Duration” means the window in which the drug may help an erection during sexual stimulation. It does not mean an erection that lasts that long.

Most used generic

Sildenafil

Viagra

  • Onset about 30–60 minutes
  • Effect studied out to about 4 hours
  • High-fat meal delays the peak by about an hour
  • Labeled doses 25, 50, and 100 mg
Sildenafil guide

Longest window

Tadalafil

Cialis

  • May help for up to 36 hours
  • Taken without regard to meals
  • As-needed or once-daily low dose
  • Also labeled for benign prostatic hyperplasia
Tadalafil guide

Another short window

Vardenafil

Levitra, Staxyn

  • Often taken about 60 minutes before
  • Film-coated doses include 5, 10, and 20 mg
  • Staxyn is a 10 mg tablet that dissolves on the tongue
  • Avoided with some QT-prolonging drugs
Vardenafil and avanafil

Fastest labeled onset

Avanafil

Stendra

  • 100 mg or 200 mg as early as about 15 minutes
  • 50 mg is timed closer to 30 minutes
  • May be taken with or without food
  • Not used with strong CYP3A4 inhibitors
Vardenafil and avanafil

Filter the full matrix

Three safety pillars

1. Heart medicines come first

Organic nitrates and guanylate cyclase stimulators are contraindications. The combination can drop blood pressure enough to cause fainting, a heart attack, or a stroke. Chest pain after an ED pill is an emergency, and a nitrate spray from a cabinet is the wrong response.

Nitrate and cardiac risks

2. The source of the pill matters

A lawful U.S. supply is a prescription from a licensed clinician and a pharmacy licensed where it dispenses. Counterfeit tablets and “herbal” male-enhancement products have been found to contain hidden PDE5 inhibitors at unknown doses.

How to check a pharmacy

3. Know the emergency signs

Headache, flushing, and nasal congestion are common and usually fade. An erection lasting longer than 4 hours, sudden loss of vision, or sudden hearing loss needs urgent care. Do not wait those out overnight.

Side effects and priapism

The rest of the guide

Food, alcohol, and other drugs

High-fat meals, grapefruit, CYP3A4 inhibitors, alpha-blockers, and alcohol.

How counterfeits fail an inspection

Packaging, imprint, and why a chemical test beats a visual guess.

Gas-station and herbal pills

FDA warnings on undeclared sildenafil, tadalafil, and chemical analogues.

What a real prescription visit covers

Heart history, medicine review, and why a checkbox website is not a clinician.

Psychological and physical causes

Performance anxiety, blood vessels, nerves, hormones, and medicines that cause ED.

Lifestyle changes and other treatments

Exercise, weight, sleep apnea, devices, and options a urologist may offer.