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. A newer form of the medicine that dissolves on the tongue might work faster than the pill that you swallow. These small differences affect the way each medication works, such as how quickly it takes effect and wears off, and the possible side effects. This medicine works best when you take it on an empty stomach an hour before sex. These include itraconazole Sporanox, Tolsura , ketoconazole Extina, Ketozole, others and ritonavir Norvir. Its effects might last longer if you have mild to moderate ED.Best subscription service for Viagra and generic Viagra: Rex MD Viagra Although erectile dysfunction (ED) may be an upsetting diagnosis for some, many people find their . Can I buy generic Viagra without a prescription? No. In most countries, including the United States, Viagra is not available without a prescription. Drug Images What is Viagra? Viagra is a brand-name prescription drug that’s approved to treat erectile dysfunction (ED). With ED, you’re unable to have or maintain an erection. .