The body takes longer to absorb it after a high-fat meal or alcohol. Medicines that block an enzyme called CYP3A4. The information provided is for educational purposes only and is not intended to replace discussions with a healthcare provider. How oral medicines differ Each oral medicine for ED has a slightly different chemical makeup. The products discussed in this site may have different product labeling in different countries.The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 . The Savings Offer and Program expire on 12/31/ For further information, call , visit test1.ru, or write: Viatris Inc., P.O. Box , Mission, KS . Cialis is only available by prescription in the United States. Viagra: Additionally, a study from Trusted Source. found that combining L-arginine and sildenafil (Viagra) worked .