Kidney disease, severe or Liver disease, severe—Use with caution. Generic versions of this low-dose form of sildenafil have been available in the U. John’s wort. Different brands may not work the same way. Trying a Free Trial of Viagra Trying a free sample of Viagra before making a full purchase provides several benefits.Used for Erectile Dysfunction. Sildenafil (Viagra) is taken by mouth to treat erectile dysfunction (ED). You take it only as needed, typically about an hour before sexual activity (but you can take it anywhere between 30 minutes to 4 hours before sex). Don’t take sildenafil (Viagra) more than once a day because doing so can put you at higher.  · Viagra treats erectile dysfunction (ED) in adults. It’s usually taken about 1 hour before sexual activity. Below, you’ll find information about recommended dosages and how to take Viagra. Viagra (sildenafil) is a prescription drug that’s used to treat erectile dysfunction (ED). The drug comes as a tablet you’ll take by swallowing. It’s usually taken as needed about 1 hour before.