Hydrochlorothiazide belongs to the group of medications called diuretics. It is also an antihypertensive. It is used to decrease fluid retention (edema) caused by congestive heart failure, certain kidney or liver problems, and medications such as corticosteroids (e.g., prednisone) and estrogen. It is also used to lower high blood pressure and treat toxemia (suddenly occurring high blood pressure and fluid retention) in pregnancy. Hydrochlorothiazide works by making the body lose excess water and salt.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

To reduce fluid retention (edema), the usual recommended adult dose of hydrochlorothiazide is 25 mg to 200 mg daily, given in 1 to 2 divided doses. Some people may only need to take this medication every other day, or for 3 to 5 days per week, as directed by their doctor. For infants and children, the dose is based on body weight and is given in 2 divided doses.

When treating toxemia of pregnancy, the recommended dose is usually 100 mg taken every day; however doses may range from 100 mg every day to 100 mg every 4 days. If needed, the dose may be increased to 200 mg daily for severe toxemia given in 2 divided doses and for short periods of time.

For the treatment of high blood pressure, the usual recommended starting adult dose of hydrochlorothiazide is 12.5 mg to 100 mg daily.

When taken once daily, this medication should be taken in the morning to prevent the need to urinate during nighttime.

Many things can affect the dose of a medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important that this medication be taken exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from light and moisture, and keep it out of the reach of children.

Do not take hydrochlorothiazide if you:

• are allergic to hydrochlorothiazide or any of the ingredients of the medication
• are allergic to sulfonamide medications (e.g., sulfamethoxazole)
• are unable to urinate
• have kidney disease that is worsening and reduced urine production while taking this medication

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• constipation
• decreased sexual interest or ability
• diarrhea
• dizziness or lightheadedness when getting up from a lying or sitting position
• headache
• increased sensitivity of skin to sunlight (skin rash, itching, redness, other discoloration of skin, or severe sunburn after exposure to sunlight)
• nausea
• loss of appetite
• pins and needles feeling in fingers
• restlessness
• upset stomach
• vomiting

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• muscle cramps or spasms
• muscle pain or weakness
• pinpoint red spots on skin
• signs of anemia (low red blood cells; e.g., dizziness, pale skin, unusual tiredness or weakness, shortness of breath)
• signs of clotting problems (e.g., unusual nosebleeds, bruising, blood in urine, coughing blood, bleeding gums, cuts that don't stop bleeding)
• signs of infection (symptoms may include fever or chills, severe diarrhea, shortness of breath, prolonged dizziness, headache, stiff neck, weight loss, or listlessness)
• signs of kidney problems (e.g., change in the amount or colour of urine, increased urination at night, blood in the urine, swelling in the feet or legs)
• signs of liver problems (e.g., nausea, vomiting, diarrhea, loss of appetite, weight loss, yellowing of the skin or whites of the eyes, dark urine, pale stools)
• signs of too much potassium loss (dryness of mouth, increased thirst, irregular heartbeat, mood or mental changes, muscle cramps or pain, nausea or vomiting, unusual tiredness or weakness, weak pulse)
• signs of too much sodium loss (confusion, convulsions, decreased mental activity, irritability, muscle cramps, unusual tiredness or weakness)
• skin growths or changes to existing skin moles or growths
• stomach pain (severe) with nausea and vomiting
• swollen glands in the mouth
• symptoms of high blood sugar (e.g., frequent urination, increased thirst, excessive eating, unexplained weight loss, poor wound healing, infections, fruity breath odour)
• tingling or burning sensation
• vision changes (e.g., blurred vision, eye pain, increased pressure in the eye)

Seek immediate medical attention if any of the following occur:

• signs of a serious allergic reaction (e.g., abdominal cramps, difficulty breathing, nausea and vomiting, or swelling of the face and throat)
• signs of pancreatitis (e.g., abdominal pain on the upper left side, back pain, nausea, fever, chills, rapid heartbeat, swollen abdomen)
• signs of a severe skin reaction such as blistering, peeling, a rash covering a large area of the body, a rash that spreads quickly, or a rash combined with fever or discomfort

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Diabetes: Hydrochlorothiazide may make it more difficult for people with diabetes to control their blood sugar. If you have diabetes, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Fluid and electrolyte balance: The levels of electrolytes such as potassium, sodium, magnesium, and chloride can be reduced with hydrochlorothiazide. Your doctor will monitor your electrolyte levels with blood tests while you are taking this medication. Warning signs or symptoms of fluid and electrolyte imbalance include:

• confusion
• drowsiness
• dry mouth
• low blood pressure
• muscle pains or cramps
• muscular fatigue
• nausea and vomiting
• racing heartbeat
• restlessness
• seizures
• thirst
• unusual tiredness
• weakness

If you experience any of these symptoms, contact your doctor. To prevent low potassium levels, eat foods that are high in potassium (e.g., bananas, dried figs, dates, prunes, nuts). If your potassium level is low, your doctor may suggest a potassium supplement.

Glaucoma: This medication may cause the symptoms of glaucoma (increased pressure in the eye) to become worse. If you have glaucoma, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed. Report any changes in vision to your doctor as soon as possible while you are taking this medication.

Gout: This medication may aggravate or cause gout. If you have high levels of uric acid in your blood or a history of gout, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Kidney function: Hydrochlorothiazide may cause changes in kidney function. If you have reduced kidney function, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Liver disease: If you have reduced liver function or progressive liver disease, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Low blood pressure when standing: This medication can cause low blood pressure when standing from a sitting or lying position (also called orthostatic hypotension). Alcohol and other medications such as phenobarbital and other medications to treat high blood pressure can increase the chances that this will happen. If you are taking these medications, your doctor may change the dose of these medications and increase them slowly to reduce the chance of you experiencing this.

Sensitivity to sunlight: This medication may increase the sensitivity of the skin to sunlight, increasing the risk of sunburn. Avoid exposure to sunlight for long periods of time, particularly between the hours of 10 am and 2 pm, while you are taking this medication and for 7 days after completing treatment. Wear a broad-spectrum sunscreen and lip balm with an SPF of 30 or higher. If you notice any unusual skin rash or peeling, contact your doctor immediately.

Skin cancer: Long-term use of hydrochlorothiazide has recently been connected to an increased risk of developing non-melanoma skin cancer. This often appears as a lump or discoloured patch of skin that slowly changes appearance or size. Check your skin regularly for unusual growths or discolouration, and report any changes to your doctor as soon as possible. Talk to your doctor about any concerns you may have.

Systemic lupus erythematosus: This medication can worsen or activate the symptoms of lupus. If you experience swollen and painful joints, fever, fatigue, or rash on the nose and cheeks while taking this medication, contact your doctor.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: This medication passes into breast milk. If you are a breast-feeding mother and are taking hydrochlorothiazide, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

There may be an interaction between hydrochlorothiazide and any of the following:

• aclidinium
• alcohol
• aldesleukin
• allopurinol
• alpha-blockers (e.g., alfuzosin, doxazosin, tamsulosin)
• amiodarone
• amphetamines (e.g., dextroamphetamine, lisdexamfetamine)
• amphotericin B
• angiotensin converting enzyme inhibitors (ACEIs; captopril, enalapril, ramipril)
• angiotensin receptor blockers (ARBs; e.g., valsartan)
• antihistamines (e.g., cetirizine, doxylamine, diphenhydramine, hydroxyzine, loratadine)
• antipsychotics (e.g., cariprazine, chlorpromazine, clozapine, haloperidol, olanzapine, quetiapine, risperidone)
• apomorphine
• atropine
• barbiturates (e.g., butalbital, phenobarbital)
• benztropine
• bortezomib
• brimonidine
• bromocriptine
• buprenorphine
• calcium supplements (e.g., calcium carbonate, calcium citrate)
• cat's claw
• cholestyramine
• clidinium
• colesevelam
• colestipol
• conivaptan
• corticosteroids (e.g., dexamethasone, hydrocortisone, prednisone)
• cyclobenzaprine
• cyclophosphamide
• darifenacin
• desmopressin
• dexmedetomidine
• diabetes medications (e.g., acarbose, dapagliflozin, glyburide, insulin, metformin, rosiglitazone)
• diazoxide
• digoxin
• dinutuximab
• disopyramide
• other diuretics (water pills; e.g., bumetanide, furosemide)
• duloxetine
• fesoterodine
• flunarizine
• glycopyrrolate
• ipratropium
• ivabradine
• ketotifen
• levodopa
• lithium
• methadone
• methotrexate
• methylphenidate
• moclobemide
• monoamine oxidase inhibitors (MAOIs; e.g., moclobemide, rasagiline, selegiline, tranylcypromine)
• multivitamin/mineral supplements
• nabilone
• narcotics (e.g., codeine, fentanyl, oxycodone, morphine, tramadol)
• nitrates (e.g., nitroglycerin, isosorbide dinitrate, isosorbide mononitrate)
• nonsteroidal anti-inflammatory drugs (NSAIDS; e.g., celecoxib, ibuprofen, naproxen, diclofenac)
• obinutuzumab
• orphenadrine
• oxybutynin
• pentoxifylline
• phosphodiesterase 5 inhibitors (e.g., sildenafil, tadalafil, vardenafil)
• pizotifen
• pramipexole
• primidone
• propiverine
• riociguat
• ropinirole
• rotigotine
• sacubitril
• selective serotonin reuptake inhibitors (SSRIs; e.g., escitalopram, citalopram, fluoxetine, paroxetine, sertraline, vortioxetine)
• sodium phosphates
• solifenacin
• sotalol
• tizanidine
• tolterodine
• topiramate
• tretinoin
• tricyclic antidepressants (e.g., amitriptyline, clomipramine, desipramine, trimipramine)
• trospium
• umeclidinium
• verteporfin
• vilazodone
• vitamin D analogues (e.g., alfacalcidol, calcifediol, calcitriol, cholecalciferol)
• yohimbine

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.