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Ensuring Your Safety With HCTZ

Some HCTZ Warnings and Precautions

Some warnings and precautions for HCTZ to be aware of include:
  • There are a number of medicines that HCTZ can interact with (see Drug Interactions With HCTZ).
  • HCTZ is more likely than other drugs to cause allergic reactions. People with a history of asthma or allergies may be more likely to have an allergic reaction to HCTZ.
Make sure to discuss these risks with your healthcare provider. Also, seek emergency medical attention immediately if you notice things such as hives, an unexplained rash, difficulty breathing, or swelling of the face or throat.
  • HCTZ may cause extreme low blood pressure in some people. Extreme low blood pressure is more likely to happen when the medicine is first started or when the dosage is changed. It is also more likely to happen in people who are on dialysis, have congestive heart failure, have diarrhea or vomiting, or who sweat a lot. This is why it is important to drink fluids regularly while taking HCTZ. If you have any possible symptoms of low blood pressure, such as dizziness, lightheadedness, or fainting, contact your healthcare provider. If you have fainted, stop taking HCTZ until you have talked to your healthcare provider.
Also, make sure not to drive, operate any heavy machinery, or perform any other tasks that require alertness until you know how HCTZ affects you.
  • People who have had a specific surgery called a sympathectomy made need lower doses of HCTZ, as it may lower blood pressure more in these people.
  • Combining HCTZ with other high blood pressure medications may lower your blood pressure too much. While it is very common to combine HCTZ with other blood pressure medications, you may need to be monitored more closely for low blood pressure when first starting these medications.
  • HCTZ is a pregnancy Category B medicine. Let your healthcare provider know if you are pregnant or thinking of becoming pregnant. If you become pregnant while taking HCTZ, contact your healthcare provider (see Hydrochlorothiazide and Pregnancy for more information).
  • Medicines like HCTZ have been known to cause a decrease in kidney function, especially in certain groups (such as those with severe congestive heart failure). Let your healthcare provider know if you have symptoms such as a decrease in urine output, drowsiness, headache, or back pain. Your healthcare provider will also regularly check your kidney function with a blood test.
  • If you have liver disease (such as liver failure or cirrhosis), small changes in fluid levels in the body may cause problems. Therefore, make sure to discuss this with your healthcare provider before taking HCTZ.
  • HCTZ may affect electrolytes in the blood (including sodium, calcium, potassium, magnesium, and chloride). Therefore, your healthcare provider will regularly check these levels. If you notice any symptoms of a possible electrolyte imbalance, contact your healthcare provider. These symptoms may include:


    • Dry mouth
    • Increased thirst
    • Weakness
    • Tiredness
    • Restlessness
    • Seizures
    • Confusion
    • Muscle pain or cramps
    • Decrease in urine output
    • Weak or irregular heartbeat
    • Nausea or vomiting.


  • In rare cases, parathyroid problems have been reported in people taking HCTZ. Also, HCTZ should be stopped before having a parathyroid function test. As part of parathyroid tests, calcium levels are often checked, and HCTZ can cause increased calcium levels.
  • HCTZ has been reported to worsen systemic lupus erythematosus or, in some cases, to even cause the condition.


  • HCTZ can sometimes cause a potentially dangerous eye reaction (a particularly dangerous type of glaucoma). This reaction usually occurs within days to weeks of starting the drug. Because this reaction can permanently damage vision, let your healthcare provider know right away if you develop vision changes and/or eye pain. The main treatment for this reaction is to stop taking this medication, although other treatment, including surgery, may sometimes be necessary. 


  • HCTZ is also known to worsen gout.
  • HCTZ may cause high blood sugar (hyperglycemia) in people with diabetes or, in some cases, even cause diabetes in people without a history of the condition.
  • HCTZ may increase levels of cholesterol and triglycerides in the blood.
  • HCTZ passes through breast milk. Therefore, if you are breastfeeding or plan to start breastfeeding, be sure to talk with your healthcare provider about this. He or she can decide if taking HCTZ while nursing would be okay for your particular situation.
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