Hydrochlorothiazide warnings: what you should know

Hydrochlorothiazide (HCTZ) is a thiazide diuretic (or “water pill”) used to treat high blood pressure or swelling by helping your body get rid of excess water, sodium, and chloride. It’s sold as a generic drug as well as under the brand names Microzide and Oretic. You may also see it in drugs that combine HCTZ with other blood pressure medications.

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Since HCTZ reduces blood pressure by removing water from the bloodstream and releasing it into the urine, you may notice that you need to pee more frequently when taking this medication. Common side effects of hydrochlorothiazide include constipation or diarrhea, headache, erectile dysfunction, loss of appetite, nausea, vomiting, vision problems, and weakness. The higher the dose, the more people experienced side effects. In clinical trials, patients taking doses of 12.5 mg experienced the same rate of side effects as those given a placebo (DailyMed, 2014).

This medication may also cause high uric acid levels in the blood (hyperuricemia). The buildup of uric acid in the body can lead to the development of a condition called gout, a painful type of arthritis characterized by sudden pain, redness, and swelling of the joints (Jin, 2012). This is more common in patients with a history of gout and those with impaired kidney function. For people with a history of gout, hydrochlorothiazide may make symptoms worse (DailyMed, 2014).

Since hydrochlorothiazide is used to lower blood high blood pressure, in some cases, it can cause low blood pressure, a condition known as hypotension. Symptoms of low blood pressure include dizziness, blurry vision, fatigue, shallow breathing, rapid heart rate, confusion, and fainting. Drinking alcohol may increase your chances of experiencing low blood pressure while taking hydrochlorothiazide (DailyMed, 2014).

People taking hydrochlorothiazide may also experience kidney problems, or, in rare cases, liver problems. These liver problems may cause jaundice, a yellowing of the skin and eyes (NIH, 2017).

Serious side effects

Hydrochlorothiazide affects electrolyte and fluid balance in the body, which can have serious side effects. This medication may cause low sodium levels (hyponatremia), low potassium levels (hypokalemia), and low magnesium levels (hypomagnesemia). Electrolyte imbalances can cause dry mouth, irregular heartbeats (arrhythmias), muscle aches, nausea, thirst, tiredness, vomiting, and weakness. In some cases, these conditions can be dangerous and even life-threatening (DailyMed, 2014). If you experience any electrolyte imbalance symptoms such as dry mouth, weakness, restlessness, confusion, or muscle pains, seek medical help right away (NIH, 2019).

Some people can have an allergic reaction to HCTZ (FDA, 2011). This diuretic is a sulfonamide, a medication that uses sulfa, so people with an allergy to sulfa drugs should not take hydrochlorothiazide. An allergic reaction may cause hives, shortness of breath, trouble breathing, wheezing, skin rash, or swelling of the face, tongue, or throat. Seek medical attention immediately if you experience any of these signs of an allergic reaction.

Talk to your healthcare provider about any other prescription drugs, over-the-counter medications, and supplements that you are taking before starting hydrochlorothiazide.

Some drugs, like cholesterol-lowering medications and pain killers (like ibuprofen), may decrease the effectiveness of HCTZ. Speak to a healthcare professional about what medications you can take while taking HCTZ (DailyMed, 2014).

Combining HCTZ with controlled substances like alcohol, as well as drugs like barbiturates and narcotics, can increase the risk of developing dangerously low blood pressure. For people with adrenal insufficiency receiving treatment with corticosteroids or a hormone called ACTH, the combination of these drugs with HCTZ can increase your risk of dangerous electrolyte imbalances. Low potassium levels, in particular, can cause irregular heart rhythms. Discuss this with your healthcare provider before starting hydrochlorothiazide (DailyMed, 2014).

This list does not include all drug interactions with hydrochlorothiazide, and others may exist. Get medical advice from your healthcare provider or pharmacist for more information. 

There may be an increased risk of side effects for some people who take hydrochlorothiazide. For pregnant women who experience swelling due to a pathological condition, treatment with hydrochlorothiazide may be appropriate. HCTZ is considered pregnancy category B—this means that there are no proven risks in humans. HCTZ has been shown to enter breast milk, so healthcare providers recommend either not taking this medication while breastfeeding or not breastfeeding if you need this treatment. Patients who are breastfeeding should consult with their healthcare provider about which treatment options are best for them (DailyMed, 2014).

Individuals with diabetes who are taking anti-diabetic medications (like insulin) may need to monitor their blood glucose levels more closely while taking HCTZ. Hydrochlorothiazide may make it more difficult for them to control blood glucose, and people with diabetes may need adjustments to their anti-diabetic medications.

Certain people are at an increased risk of severe side effects from HCTZ. This includes people with adrenal insufficiency and individuals with gout. This medication is not effective in patients with severe kidney failure and should be used with caution in patients with various kidney conditions, as this may increase the risk of side effects from the medication (DailyMed, 2014). 

Hydrochlorothiazide should not be used by patients with severe liver disease. Before starting any prescription medication, consult with your healthcare provider to find the treatment that’s right for you (DailyMed, 2014).

Zestoretic is a prescription drug that combines lisinopril and HCTZ into one tablet. Lisinopril is a blood pressure medication called angiotensin-converting enzyme inhibitor, or ACE inhibitor. Since Zestoretic includes HCTZ, many of the warnings of this medication are the same as those that come with being treated with HCTZ alone.

Zestoretic may cause symptoms of an allergic reaction (hypersensitivity) in certain people. Lisinopril in these tablets may cause swelling of the face, tongue, lips, and extremities. This may happen at any time during treatment and without warning. Lisinopril is more likely to cause angioedema in Black people. This reaction is also more common in women than in men and in smokers than in nonsmokers (Byrd, 2006). If you experience this type of swelling, stop taking Zestoretic, and get medical help right away (DailyMed, 2019).

You should also get medical attention right away if you experience fainting (syncope), stomach pain with or without nausea or vomiting, and yellowing of the skin or eyes (jaundice). In rare cases, lisinopril can cause kidney damage that leads to kidney failure. This can be fatal (DailyMed, 2019).

Lisinopril is considered pregnancy category D—that means there is evidence that this drug may harm the fetus, but potential benefits may outweigh the potential risks in certain people. In general, this medication should not be used at all after the first three months (first trimester) of pregnancy. Lisinopril can cause potentially fatal damage to the fetus if taken during this time. If you take lisinopril or any medication for management of high blood pressure, make sure to tell your healthcare provider if you become pregnant or wish to become pregnant. An adequate treatment plan is crucial to ensure healthy blood pressure during pregnancy, too (DailyMed, 2019).

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Current version

October 07, 2020

Written by

Linnea Zielinski

Fact checked by

Yael Cooperman, MD

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About the medical reviewer

Yael Cooperman, MD, Ro

Yael Cooperman is a physician and works as a Senior Manager, Medical Content & Education at Ro.