No side effects were reported in sexual partners. There were some reports of headaches and nausea, however. Side Effects Are Minimal. Its effects often last for 4 to 5 hours. This medicine works best when you take it on an empty stomach an hour before sex.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 . Sildenafil (Viagra, Revatio) is a moderately priced drug used to treat erection problems in is also used to treat pulmonary arterial hypertension, a serious heart and lung . Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric .