Follow your doctor’s orders or the directions on the label. The physiological role and clinical consequence of PDE11 inhibition in humans have not been defined. For treatment of pulmonary arterial hypertension: Adults—40 milligrams mg two 20 mg tablets taken once a day. The major circulating metabolite is the methylcatechol glucuronide. There are no available data for doses higher than 10 mg of tadalafil in patients with hepatic impairment. Do not drink excessive amounts of alcohol eg, 5 or more glasses of wine or 5 or more shots of whiskey when taking tadalafil. · If you take tadalafil for pulmonary arterial hypertension, do not take Cialis® or other PDE5 inhibitors, such as sildenafil (Revatio® or Viagra®) or vardenafil (Levitra®). .  · The recommended dose of tadalafil tablet is 40 mg (two 20 mg tablets) taken once daily with or without food. Dividing the dose (40 mg) over the course of the day is not recommended. Mild (creatinine clearance 51 to 80 mL/min) or moderate (creatinine clearance 31 to 50 mL/min): Start dosing at 20 mg once daily. Creatinine clearance less than 30 mL/min or on hemodialysis: Tadalafil tablets for once daily use is not recommended When tadalafil 20 mg was administered with a lower dose of alcohol ( g/kg, which is equivalent to approximately 4 ounces of proof vodka, administered in less than 10 minutes), orthostatic hypotension was not observed.