Blood samples should be taken in the morning, approximately two hours after waking up, while the patient is seated for 5 to 15 minutes. Four weeks prior to testing: Spironolactone, eplerenone, drospirenone-containing contraceptives, triamterene, and amiloride must be discontinued. During this time, the consumption of licorice and chewing tobacco should also be avoided. Permitted antihypertensive medications include primarily peripheral alpha-blockers (e.g., doxazosin) and non-dihydroperidine calcium channel blockers (e.g., verapamil). Additionally, potassium levels should be normalized before each measurement. The patient should be advised to follow a balanced diet with regard to salt intake.