BMA Concise Guide to Medicine & Drugs


Brand names None

Used in the following combined preparations Acezide, Capozide, Cozaar Comp, Dyazide, Moduretic, and others


Drug group Thiazide diuretic

Overdose danger rating Low

Dependence rating Low

Prescription needed Yes

Available as generic No


Hydrochlorothiazide belongs to the thiazide group of diuretic drugs, which remove excess water from the body and reduce oedema (fluid retention) in people with congestive heart failure, kidney disorders, cirrhosis of the liver, and premenstrual syndrome. It is also used in combination with other antihypertensives, to treat high blood pressure (see Antihypertensive drugs). Hydrochlorothiazide increases potassium loss in the urine, which can cause a variety of symptoms (see diuretics), and increases the likelihood of irregular heart rhythms, particularly in patients who are taking drugs such as digoxin. For this reason, potassium supplements or potassium-sparing diuretics are often given with hydrochlorothiazide.


Your drug prescription is tailored for you. Do not alter dosage without checking with your doctor.

How taken/used Tablets.

Frequency and timing of doses Once daily, or every 2 days, early in the day.

Adult dosage range Hypertension 25–50mg daily. Oedema 25–100mg daily.

Onset of effect Within 2 hours.

Duration of action 6–12 hours.

Diet advice Use of this drug may reduce potassium in the body. Eat plenty of fresh fruit and vegetables. Discuss with your doctor the advisability of reducing your salt intake.

Storage Keep in original container at room temperature out of the reach of children. Protect from light.

Missed dose No cause for concern, but take as soon as you remember. However, if it is late in the day do not take the missed dose, or you may have to get up during the night to pass urine. Take the next scheduled dose as usual.

Stopping the drug Do not stop the drug without consulting your doctor; symptoms may recur.

Exceeding the dose An occasional unintentional extra dose is unlikely to be a cause for concern. But if you notice any unusual symptoms, or if a large overdose has been taken, notify your doctor.


Side effects from hydrochlorothaizide are generally rare, and most are caused by excessive loss of potassium in the urine, which can usually be corrected by taking a potassium supplement. They include muscle cramps, lethargy, dizziness, headache, nausea, vomiting, constipation, and temporary erectile dysfunction (impotence). Rarely, gout may occur in susceptible people, and certain forms of diabetes may become more difficult to control. Report nausea, vomiting, or constipation to your doctor. If a rash occurs, stop taking the drug and consult your doctor promptly.


Non-steroidal anti-inflammatory drugs (NSAIDs) Some NSAIDs may reduce the diuretic effect of hydrochlorothiazide, whose dosage may need to be adjusted.

Anti-arrhythmic and digitalis drugs increase the risk of toxicity from low blood potassium with hydrochlorothiazide.

Corticosteroids These drugs further increase loss of potassium from the body when taken with hydrochlorothiazide, and may reduce its diuretic effect.

Lithium Hydrochlorothiazide may increase lithium levels in the blood, leading to a risk of serious adverse effects.


Be sure to tell your doctor if:

· You have long-term liver or kidney problems.

· You have had gout.

· You have diabetes.

· You are taking other medicines.

Pregnancy Safety in pregnancy not established. Discuss with your doctor.

Breast-feeding The drug passes into the breast milk, but at normal doses adverse effects on the baby are unlikely. Discuss with your doctor.

Infants and children Not usually prescribed. Reduced dose necessary.

Over 60 Increased likelihood of adverse effects.

Driving and hazardous work Avoid such activities until you have learned how hydrochlorothiazide affects you because the drug may reduce mental alertness and cause dizziness.

Alcohol Keep consumption low. Hydrochlorothiazide increases the likelihood of dehydration and hangovers after consumption of alcohol.


Excessive loss of potassium and imbalances of other salts may result.

Monitoring Blood tests may be performed periodically to check kidney function and levels of potassium and other salts.