Side Effects for Hydrochlorothiazide

Hydrochlorothiazide is the most commonly prescribed diuretic, or "water pill," in the United States. It is used to treat conditions such as high blood pressure, heart failure and edema -- excess fluid accumulation. Hydrochlorothiazide is available in capsules or tablets, alone or in combination with other medications used to treat high blood pressure.

A close-up of a doctor writing a prescription at a desk. (Image: Wavebreakmedia Ltd/Wavebreak Media/Getty Images)

Electrolyte Imbalance

Diuretics work by increasing the amount of electrolytes, such as sodium, potassium and magnesium, excreted in the urine. As these electrolytes are filtered out of the blood, they pull fluid with them to decrease blood volume. Diuretics like hydrochlorothiazide can cause low levels of sodium, potassium and magnesium. Low levels of electrolytes are detected in routine blood tests. If an electrolyte imbalance develops, your doctor may prescribe supplements or dietary changes to correct the problem.

Elevated Blood Sugar

Reducing the fluid volume of blood may increase the concentration of glucose, or blood sugar. Most of the time, your body is able to adjust and keep your blood sugar level within a normal range. If you have diabetes, however, your blood sugar level may increase.

High Cholesterol

When you begin taking hydrochlorothiazide, your cholesterol level could increase by as much as 5 to 15 percent. Your cholesterol may return to its previous level after you have been on hydrochlorothiazide for several months.

Sun Sensitivity

Hydrochlorothiazide can cause sun sensitivity. This means that you may sunburn more quickly and easily than you did before you began taking hydrochlorothiazide. Applying sunscreen before you go out in the sun can help protect against sunburn.

Sulfa Reaction

Hydrochlorothiazide is a sulfonamide, which means its chemical structure is similar to the sulfa antibiotics. People who are allergic to sulfa antibiotics may be allergic to hydrochlorothiazide as well. Symptoms of an allergic reaction include a rash, itching, hives and wheezing or shortness of breath. If you experience skin symptoms that may indicate an allergic reaction, stop taking the medication and contact your doctor. If you experience difficulty breathing, seek emergency medical care.


Gout is a condition in which extra uric acid in the blood crystallizes and deposits in a joint, usually the big toe. Gout is characterized by redness and swelling of the affected joint that causes extreme pain. The reduced fluid volume of blood caused by hydrochlorothiazide can further increase the concentration of uric acid in the blood. This can trigger gout in people who have never had it before, or lead to flareups in people previously diagnosed with gout.

Stevens-Johnson Syndrome

Because it is related to the sulfa antibiotics, people taking hydrochlorothiazide have an increased risk of developing a serious condition known as Stevens-Johnson syndrome. In Stevens-Johnson syndrome, the outer layer of the skin detaches from the body. It is an extremely rare disorder, with only about 1.9 cases per million people each year. Of these cases, up to 50 percent have no known cause. When Stevens-Johnson syndrome is caused by medication, it is most likely to occur within the first month of taking the drug.

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