Blood Pressure Home > Hydrochlorothiazide Warnings and Precautions

Some Hydrochlorothiazide Warnings and Precautions

Patients taking this drug should keep the following warnings and precautions in mind:
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.
  • Hydrochlorothiazide 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 hydrochlorothiazide. 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 hydrochlorothiazide 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 hydrochlorothiazide affects you.
  • People who have had a specific surgery called a sympathectomy made need lower doses of hydrochlorothiazide, as it may lower blood pressure more in these people.
  • Combining hydrochlorothiazide with other high blood pressure medications may lower your blood pressure too much. While it is very common to combine hydrochlorothiazide with other blood pressure medications, you may need to be monitored more closely for low blood pressure when first starting these medications.
  • Hydrochlorothiazide 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 hydrochlorothiazide, contact your healthcare provider (see Hydrochlorothiazide and Pregnancy for more information).
  • Medicines like hydrochlorothiazide 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 hydrochlorothiazide.
  • Hydrochlorothiazide 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: a 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 hydrochlorothiazide. Also, hydrochlorothiazide should be stopped before having a parathyroid function test. As part of parathyroid tests, calcium levels are often checked, and hydrochlorothiazide can cause increased calcium levels.
  • Hydrochlorothiazide has been reported to worsen systemic lupus erythematosus or, in some cases, to even cause the condition.
  • Hydrochlorothiazide is also known to worsen gout.


  • Hydrochlorothiazide 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. 


  • Hydrochlorothiazide 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.
  • Hydrochlorothiazide may increase levels of cholesterol and triglycerides in the blood.
  • If you are nursing, hydrochlorothiazide passes through your 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 whether taking hydrochlorothiazide while nursing would be okay for your particular situation.
Written by/reviewed by:
Last reviewed by: Kristi Monson, PharmD;
Last updated/reviewed:
List of references (click here):
Other Articles in This eMedTV Presentation




Related Channels

eMedTV Links
Copyright © 2006-2020 Clinaero, Inc.

eMedTV serves only as an informational resource. This site does not dispense medical advice or advice of any kind. Site users seeking medical advice about their specific situation should consult with their own physician. Click Terms of Use for more information.

This site complies with the HONcode standard for trustworthy health information:
verify here.