Sildenafil is a drug that helps improve blood flow to the penis, allowing you to achieve a firm, longer-lasting erection more easily. Typically this takes the form of a tick box medical questionnaire, which is then reviewed by the pharmacist prior to supply. It lasts 4 to 5 hours, or longer if you have mild to moderate ED. Sildenafil Viagra. The body takes longer to absorb it after a high-fat meal or alcohol. Oral ED medicines might not work or might be dangerous if you also take any of the following: Nitrate medicines.Since , Viagra has been available over the counter as Viagra Connect. Both Viagra and Viagra Connect contain the same active ingredient: Sildenafil. However, Viagra . The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 . Is There Anything Over the Counter That Works Like Viagra? There are several medications and treatments used to treat erectile dysfunction (ED, impotency), including .