This leads to more blood flow to the penis, leading to stronger erections. Cialis vs. Concerning vascular causes, the risk factors for atherosclerosis including smoking, high blood pressure, diabetes diabetics do not respond well to pills like sildenafil Viagra and high cholesterol are ALSO risk factors for erectile dysfunction. How long does it take for Cialis to peak? They are PDE5 inhibitors that allow for increased blood flow to the penis, leading to more frequent and harder erections. Vardenafil Levitra is more selective than sildenafil and tadalafil Cialis to PDE5, which again means a lower dose is needed with potentially less side effects.The vagina and clitoris also contain PDE5. So, if a female takes Viagra, the drug may increase blood flow to these areas. However, female genitals contain less . Viagra takes around 30 minutes to become effective and lasts about 4 hours. Cialis lasts much longer — up to 36 hours in some cases. Stendra can start doing its thing in as little . Sildenafil (Viagra) has a half-life of 4 hours and vardenafil (Levitra) has a half-life of hours while tadalafil (Cialis) has a half-life of hours. This means that vardenafil .