Hydrochlorothiazide (HCTZ)

Hydrochlorothiazide is a thiazide diuretic, often called a water pill, used to treat high blood pressure and to reduce a build-up of fluid in the body (edema). It works by making the kidneys pass more salt and water out of the body, so you urinate more.

Hydrochlorothiazide is often shortened to HCTZ on prescriptions and medical records. It is available as a tablet, capsule, and liquid (suspension) taken by mouth and is usually taken once or twice a day.

Hydrochlorothiazide is available as:

• oral tablet (12.5 mg, 25 mg, and 50 mg)
• oral capsule (12.5 mg)
• powder for oral suspension (10 mg/mL)

Hydrochlorothiazide (HCTZ) brand names included HydroDIURIL tablets (discontinued), Esidrix (discontinued), and Microzide capsules (discontinued); now generic tablets and capsules are available. The brand name of hydrochlorothiazide oral suspension is Inzirqo.

Hydrochlorothiazide is also an ingredient in many combination blood pressure medicines, including with losartan, lisinopril, valsartan, and more.

Hydrochlorothiazide is approved to treat high blood pressure (hypertension) and fluid retention (edema) in certain patients.

High blood pressure

HCTZ is used to manage high blood pressure (hypertension), either on its own or alongside other blood pressure medicines. Lowering blood pressure reduces the risk of fatal and non-fatal cardiovascular events, mainly strokes and heart attacks.

All three forms of hydrochlorothiazide, tablets, capsules and the oral suspension, are approved for high blood pressure in adults, and the oral suspension is also approved for children.

Fluid retention

Hydrochlorothiazide tablets are used to treat a build-up of fluid (edema) associated with:

• congestive heart failure
• cirrhosis of the liver
• kidney conditions, including nephrotic syndrome, acute glomerulonephritis and chronic kidney failure
• treatment with corticosteroid or estrogen medicines

The HCTZ oral suspension is approved for fluid retention associated with congestive heart failure, cirrhosis of the liver, and kidney disease including nephrotic syndrome, in both adults and children.

The capsules are approved for high blood pressure only, not for fluid retention.

Not all forms of HCTZ are approved for all indications and age groups.

Approved HCTZ uses by age groups and dosage form

Hydrochlorothiazide works by inhibiting the kidneys from reabsorbing sodium and chloride, so more salt and water leave the body in the urine, which helps reduce excess fluid buildup (edema). Exactly how thiazides lower blood pressure is not fully understood. The early effect is thought to come from a drop in blood volume. With longer-term use, blood volume returns towards normal while the blood vessels themselves offer less resistance to blood flow. Hydrochlorothiazide does not usually change blood pressure that is already normal.

Hydrochlorothiazide is a thiazide diuretic.

Fluid and salt imbalance

Hydrochlorothiazide can lower the levels of potassium, sodium, magnesium and chloride in your blood. Low potassium (hypokalemia) is the most common of these and is more likely at higher doses, during rapid fluid loss, if you have severe cirrhosis, or after long-term use.. Your doctor will check your blood before you start and at intervals during treatment.

Contact your doctor if you have any of the following, which can be signs of a fluid or salt imbalance:

• dry mouth, thirst, or unusual weakness or tiredness
• drowsiness, restlessness or confusion
• muscle pain, cramps or muscle fatigue
• fast heartbeat
• passing much less urine than usual
• nausea or vomiting
• seizures

Kidney and liver problems

HCTZ reduces the fluid volume in your body, which can lead to sudden kidney injury. The risk is higher if you have chronic kidney disease, heart failure, or are already low on fluid. If you have liver disease, small changes in fluid and salt balance can trigger a serious complication called hepatic coma. Your doctor will monitor your kidney function and watch for changes in alertness.

Sudden vision changes need urgent care

Rarely, hydrochlorothiazide causes sudden short-sightedness (acute myopia) and a sharp rise in pressure inside the eye (acute angle-closure glaucoma), usually within hours to weeks of starting the medicine. Stop taking it and get medical help immediately if your vision drops suddenly or your eye hurts. Left untreated, this can cause permanent loss of vision. A history of allergy to sulfa medicines or penicillin may increase the risk.

Blood sugar, cholesterol, uric acid and calcium

Hydrochlorothiazide can raise blood sugar, cholesterol, triglycerides, uric acid and calcium. Your diabetes medicine or insulin dose may need adjusting, and diabetes that was previously unnoticed can become apparent during treatment. The rise in uric acid is related to the dose and can cause gout or make existing gout worse. Because the medicine also affects calcium, it is stopped before parathyroid function tests, so tell any doctor arranging tests that you take it. Your doctor will check these levels from time to time.

Skin cancer risk

Long-term use of hydrochlorothiazide is linked to a small increase in the risk of non-melanoma skin cancer, mainly squamous cell carcinoma. In a large safety study the increase was about 1 extra case per 16,000 people per year, rising to about 1 extra case per 6,700 people per year among white patients who had taken a total of 50,000 mg or more.

Protect your skin from the sun, wear protective clothing and use sunscreen, avoid sunlamps and tanning beds, and have regular skin checks. Tell your doctor about any new or changing skin growth, or a sore that does not heal.

Lupus and allergic reactions

Thiazide diuretics have been reported to worsen lupus or bring it on. Sensitivity reactions can happen whether or not you have a history of allergies or asthma.

Do not take hydrochlorothiazide if you are unable to pass urine (anuria), or if you are allergic to hydrochlorothiazide or to other sulfonamide-derived medicines (sometimes called sulfa drugs).

Before you start HCTZ, tell your doctor if you have or have ever had:

• kidney disease or reduced kidney function
• liver disease, including cirrhosis
• diabetes
• gout or high uric acid levels
• high cholesterol or high triglycerides
• high calcium levels or a parathyroid gland disorder
• low potassium or low sodium levels
• lupus (systemic lupus erythematosus)
• glaucoma
• an allergy to sulfa medicines or to penicillin

Also tell your doctor if you are pregnant, planning to become pregnant, or breastfeeding. Hydrochlorothiazide may cause jaundice or bleeding problems in a newborn. It can also pass into breast milk and may cause serious side effects in a nursing baby, so you and your doctor should decide whether you will take this medicine or breastfeed.

The most noticeable effect of hydrochlorothiazide is passing urine more often, particularly in the first few weeks. This is how the medicine works rather than a side effect, and it usually settles as your body adjusts.

Serious side effects

Get emergency medical help if you have signs of an allergic reaction, such as hives, difficulty breathing, or swelling of your face, lips, tongue or throat.

Get emergency medical help if you have a severe skin reaction, such as a spreading red or purple rash with blistering and peeling, or skin that is painful to touch.

Stop taking hydrochlorothiazide and get medical help immediately if you have a sudden change in your vision or pain in your eye.

Call your doctor at once if you have:

• severe pain in your upper stomach that spreads to your back, with nausea and vomiting, which can be a sign of inflammation of the pancreas (pancreatitis)
• yellowing of your skin or the whites of your eyes (jaundice)
• fever, chills, sore throat, mouth sores or other signs of infection
• unusual bruising or bleeding, or pale skin and unusual tiredness, which can be signs of a blood problem
• shortness of breath, wheezing, or a cough with frothy mucus
• passing much less urine than usual, or swelling in your legs and ankles
• light-headedness or fainting, especially when standing up
• signs of dehydration or a salt imbalance, such as extreme thirst, dry mouth, confusion, muscle cramps, irregular heartbeat or unusual weakness

Other side effects

Other hydrochlorothiazide side effects include:

• dizziness, a spinning sensation (vertigo), headache, restlessness, or tingling and numbness (paresthesia)
• weakness
• nausea, vomiting, diarrhea, constipation, stomach cramping, stomach irritation, or loss of appetite
• muscle spasm
• increased sensitivity to sunlight, causing sunburn more easily
• hair loss or thinning
• difficulty getting or keeping an erection
• temporary blurred vision, or objects looking yellow-tinged (xanthopsia)
• swelling and tenderness of the salivary glands
• raised blood sugar, sugar in the urine, or raised uric acid

If a side effect is moderate or severe, your doctor may lower your dose or stop the medicine. Do not stop taking HCTZ on your own without speaking to your doctor first.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Your doctor will choose the smallest dose that controls your condition, and may adjust it over time. Follow your prescription label and do not change your dose yourself.

HCTZ dose for high blood pressure (adults)

Tablets: The starting dose is hydrochlorothiazide 25 mg once a day, which may be increased to 50 mg a day, taken as a single dose or split into two doses. Doses above 50 mg a day are often associated with a marked drop in blood potassium. Most people do not need more than 50 mg a day when hydrochlorothiazide is taken alongside other blood pressure medicines

Capsules: The starting dose is a hydrochlorothiazide 12.5 mg capsule once a day, whether taken on its own or with other blood pressure medicines. Total daily doses above 50 mg are not recommended. Capsules are approved for high blood pressure only, not for fluid retention.

HCTZ dose for fluid retention (adults)

Tablets: The usual dose is hydrochlorothiazide 25 mg to 100 mg a day, taken as a single dose or split into two doses. Many people with fluid retention respond to intermittent treatment, such as taking it every other day or on 3 to 5 days each week. Excessive response and undesirable electrolyte imbalance are less likely to occur with intermittent dosing.

HCTZ dose for children for high blood pressure and fluid retention

The usual HCTZ dose in children, for both high blood pressure and fluid retention, is 1 mg to 2 mg per kilogram of body weight (0.5 mg to 1 mg per pound) a day, given as a single dose or split into two doses.

• Infants under 6 months: may be need doses of up to 3 mg per kilogram (1.5 mg per pound) a day, given as two divided doses up to the same maximum 37.5 mg daily limit
• Infants and children under 2 years: do not exceed 37.5 mg a day
• Children 2 to 12 years: do not exceed 100 mg a day

The dose is based on your child's weight and must be worked out by their doctor.

Taking the oral suspension

If your child has been prescribed the liquid form (oral suspension), the following applies:

• Shake the bottle well before every dose.
• Measure each dose with the oral dosing syringe. Ask your pharmacist for a syringe and a bottle adapter if you do not have them.
• Never measure a dose with a household teaspoon or tablespoon, because these do not give an accurate amount.
• Store the made-up suspension at room temperature and do not freeze it.
• Throw away any unused suspension 30 days after it was made up. The pharmacist will write this date on the bottle.

The oral suspension can be taken with or without food.

What happens if I miss a dose?

Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Overdose symptoms may include nausea, dizziness, dry mouth, thirst, and muscle pain or weakness.

Hydrochlorothiazide starts to work within 2 hours of a dose, with the peak effect at about 4 hours. The increase in urine output lasts for around 6 to 12 hours, while the medicine's overall action on the body can persist for up to 24 hours.

Lowering blood pressure takes longer than the fluid effect, and your doctor will usually reassess your blood pressure after a few weeks rather than straight away.

The medicine is well absorbed, is not broken down by the body, and is cleared by the kidneys, with most of a dose passing out unchanged in the urine. Its half-life, meaning the time for blood levels to fall by half, has been reported as 6 to 15 hours. In people with kidney disease, levels in the blood are higher and the medicine stays in the body longer.

Hydrochlorothiazide controls high blood pressure but does not cure it. Keep taking it even if you feel well, because high blood pressure often causes no symptoms.

Tell your doctor and pharmacist about all the medicines you take, including prescription and over-the-counter medicines, vitamins, and herbal products.

Medicines that need particular care

• Lithium. Lithium and diuretics generally should not be taken together. Hydrochlorothiazide reduces how quickly the kidneys clear lithium, which carries a high risk of lithium toxicity.
• Cholestyramine and colestipol. These cholesterol-lowering resins bind hydrochlorothiazide in the gut and can reduce how much you absorb by up to 85 percent for cholestyramine and 43 percent for colestipol. The doses need to be separated. For the oral suspension, the label advises taking hydrochlorothiazide at least 4 hours before, or 4 to 6 hours after, the resin.
• NSAIDs such as ibuprofen (Advil, Motrin), naproxen (Aleve), diclofenac, meloxicam, indomethacin, celecoxib and aspirin. These can reduce the fluid-clearing and blood-pressure-lowering effects of hydrochlorothiazide, and your doctor will check whether the medicine is still working as intended.
• Insulin and oral diabetes medicines. Your diabetes medicine dose may need adjusting.
• Corticosteroids and ACTH. Taken with hydrochlorothiazide, these increase the loss of salts from the body, particularly potassium.
• Digoxin and other digitalis medicines. Low potassium caused by hydrochlorothiazide can make the heart more sensitive to the toxic effects of digitalis, including irregular heart rhythms.
• Other blood pressure medicines. The effects add together, which may be intended, but can also lower blood pressure more than expected.
• Alcohol, barbiturates and opioid pain medicines. These can make the drop in blood pressure on standing worse, causing dizziness or fainting.
• Muscle relaxants used during surgery (nondepolarizing muscle relaxants such as tubocurarine). You may respond more strongly to them, so tell your surgeon and anesthetist that you take hydrochlorothiazide.
• Medicines that raise blood pressure (pressor amines such as norepinephrine). Your response to them may be reduced, although this does not usually prevent their use.

This list is not complete. Other medicines may affect hydrochlorothiazide, and hydrochlorothiazide may affect other medicines.