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Hydrochlorothiazide: 7 things you should know

Medically reviewed by Carmen Fookes, BPharm. Last updated on March 22, 2022.

1. How it works

  • Hydrochlorothiazide is a diuretic (this means it increases urination) that works by inhibiting the reabsorption of salts in the kidneys.
  • Hydrochlorothiazide also lowers blood pressure in people with high blood pressure by an unknown mechanism; people with normal blood pressure are not usually affected by hydrochlorothiazide.
  • Hydrochlorothiazide belongs to the class of medicines known as thiazide diuretics. Hydrochlorothiazide may be abbreviated as HCTZ.

2. Upsides

  • Used in addition to other drugs to remove fluid build-up (edema) in the body caused by heart failure, liver disease, renal disease, and steroid or estrogen therapy. May be used to treat edema due to nephrotic syndrome that has not responded to corticosteroids.
  • Intermittent (as needed) therapy may be appropriate for some people with edema.
  • Used to lower blood pressure in people with high blood pressure; daily dosing is usually recommended when hydrochlorothiazide is used for this indication.
  • May be used off-label for several other indications.
  • May be used alone or in combination with other agents.
  • Orthostatic hypotension ( a drop in blood pressure when going from a lying to a sitting or standing position) rarely occurs.
  • Generic hydrochlorothiazide is available.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • A headache, dizziness on standing, dehydration, skin reactions, and depletion of electrolytes. Effects may be aggravated by alcohol, illness, or hot weather.
  • Rarely, may cause acute angle glaucoma. Symptoms include eye pain and reduced vision and may come on within hours or weeks of drug initiation.
  • May cause allergic reactions in people allergic to sulfonamide drugs.
  • Dosages greater than 50mg/day are not usually needed when hydrochlorothiazide is given in conjunction with other drugs used for hypertension. Higher dosages are also associated with greater potassium loss.
  • May precipitate gout in some people or increase cholesterol or triglyceride levels, deplete levels of certain electrolytes such as sodium, chloride, magnesium, and potassium, and increase levels of calcium.
  • May interact with some other medications, including other medications used to lower blood pressure, lithium, oral antidiabetics, corticosteroids, and NSAIDs.
  • May not be suitable for some people including those gout, diabetes, kidney or liver disease, glaucoma, or asthma. May increase cholesterol levels.
  • Regular monitoring is required especially on initiation. Blood pressure should be monitored at least monthly until controlled. Renal function and electrolytes should be monitored two to four weekly on initiation.
  • Considered a second-line agent for the management of high blood pressure during pregnancy; other antihypertensives (such as methyldopa, nifedipine, labetalol) are preferred. Not recommended for the prevention or management of gestational hypertension or preeclampsia. May be considered for moderate-to-severe edema associated with pregnancy except when caused by renal disease.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

Hydrochlorothiazide may be used to relieve edema and in the treatment of high blood pressure but may not be suitable for some people including those with sulfonamide allergies.

5. Tips

  • Dosages may need to be adjusted depending on the individual; higher dosages need extra monitoring by a doctor.
  • Report any symptoms such as confusion, dizziness, muscular weakness, and GI disturbances to a doctor.
  • Seek urgent medical advice if you are unable to urinate.
  • Report any eye pain or visual disturbances immediately to your doctor.
  • Avoid drinking alcohol while you are taking hydrochlorothiazide because this may aggravate some of the side effects such as dizziness and dehydration.
  • Be careful not to become overheated or dehydrated in hot weather while taking hydrochlorothiazide. Talk to your doctor about how much fluid you should be drinking; in some cases drinking too much fluid is just as harmful as not drinking enough fluids.
  • Talk to your doctor or pharmacist before taking any other medications at the same time as hydrochlorothiazide because some may not be suitable (including those bought over the counter).

6. Response and effectiveness

  • Hydrochlorothiazide starts to work within 2 hours and its peak effect occurs within 4 hours. The diuretic and blood pressure lowering effects of hydrochlorothiazide may last six to 12 hours.

7. Interactions

Medicines that interact with hydrochlorothiazide may either decrease its effect, affect how long it works for, increase side effects, or have less of an effect when taken with hydrochlorothiazide. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with hydrochlorothiazide include:

  • allopurinol
  • aspirin and NSAIDs, such as diclofenac, ibuprofen, or indomethacin
  • cholestyramine or colestipol
  • corticosteroids such as prednisone, betamethasone, hydrocortisone, or methylprednisone
  • corticotrophin
  • cyclosporine
  • digoxin
  • duloxetine
  • insulin
  • lithium
  • methotrexate.

People taking oral medications for diabetes may need to talk to their doctor about adjusting the dose of their medicine.

Note that this list is not all-inclusive and includes only common medications that may interact with hydrochlorothiazide. You should refer to the prescribing information for hydrochlorothiazide for a complete list of interactions.


Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use hydrochlorothiazide only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Copyright 1996-2023 Revision date: March 21, 2022.