Hello dear, Thank you for your question. Hydrochlorothiazide is one of the most common anti-hypertensive drugs used in treating high blood pressure. It can used as a sole agent or to enhance the anti-hypertensive properties of other drugs. It also is used in treating edema from liver disease, kidney disease, heart disease etc. In your mother s case the doctor prescribed it for the control of early stage blood pressure, since it was prescribed as a sole agent. This drug prevents your body from absorbing too much salt and water, which can accumulate in high amounts in the blood and increase the blood pressure. You need to measure your mother s blood pressure periodically in order to verify if the drug is being effective. The optimal target for the blood pressure is 120/80 mmHg. If the drug fails to achieve the target please don t hesitate to contact your doctor. I hope this helped. All the best, Dr. Alma