Viagra vs. Cialis vs. Other Popular ED Meds: Sildenafil (Viagra): Viagra is the most well-known ED medication, containing the active ingredient sildenafil. It is typically taken on an empty stomach an hour before sexual activity and remains effective for four to five hours. Viagra is most suitable for men with mild to moderate erectile dysfunction. <a href="https://ivermectin-12mg.com/">buy ivermectin on line</a> Potential interactions between sildenafil and nitrates can be serious or even fatal. This may include a severe drop in blood pressure, which may lead to loss of consciousness, falls, shock, or even death. For this reason, it is contraindicated (not recommended) to take nitrates and sildenafil together.