These include itraconazole Sporanox, Tolsura , ketoconazole Extina, Ketozole, others and ritonavir Norvir. They’re often the first line of treatment for trouble getting or keeping an erection, called erectile dysfunction ED. Sildenafil, the active ingredient in Viagra, was originally developed in the early s to treat cardiovascular disease. The generics cost much less, and—in the case of sildenafil—come in 20 mg doses. This medicine also works best when you take it an hour before sex on an empty stomach. Popping Cialis has some side effects—it increases your chances of limb, back and muscle pain. Kidney disease that needs to be treated with dialysis. · Viagra comes as an oral tablet that contains the active drug sildenafil. Sildenafil is also available in generic form. Viagra is classified as a phosphodiesterase type 5 (PDE5) inhibitor. Sildenafil (Viagra) and tadalafil (Cialis) are the most commonly prescribed medications for ED, and they have the longest track record. For occasional use, most people start with sildenafil. For regular use, tadalafil can be a better fit. Some people prefer to alternate between medications. All ED meds are equally safe and effective. Sildenafil (Viagra, Revatio) is a moderately priced drug used to treat erection problems in men. It is also used to treat pulmonary arterial hypertension, a serious heart and lung condition. This drug is more popular than comparable drugs. It is available in generic and brand versions.