The body takes longer to absorb it after a high-fat meal or alcohol. Follow the manufacturer’s directions to use and clean the oral syringe. Oral medicine for ED also might not be safe or work well if you have: Very low blood pressure, called hypotension, or uncontrolled high blood pressure, called hypertension. Your doctor or other health care professional can recommend one for you based on these factors, other health conditions you have and any other medicines you take. Exploring the Connection Semen retention is a topic that has gained quite a bit of attention in recent years.Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a prescription drug that’s used in . Sildenafil is in a class of medications called phosphodiesterase (PDE) inhibitors. Sildenafil treats erectile dysfunction by increasing blood flow to the penis during sexual . Sildenafil (Viagra). This medicine works best when you take it on an empty stomach an hour before sex. The body takes longer to absorb it after a high-fat meal or .