Thiazides: What are they? How do they work? Examples, Side Effects and Considerations

A diuretic is used to treat high blood pressure (hypertension).

When the heart is beating, it continuously pumps blood around the body to maintain the whole organism’s proper functioning, so as the blood moves, it is pushed against the sides of the blood vessels.

The force that generates the movement of blood is what is called blood pressure. If this condition is too high, it exerts additional pressure on all the arteries, which would generate short or long-term heart attacks and strokes.

How to know if you have high blood pressure?

Having high blood pressure ( hypertension ) is usually not something you feel or notice. Because it is the functioning or movement of blood through the arteries, it rarely generates apparent symptoms. The only way to know what blood pressure is is to measure it.

The first (top) number is systolic blood pressure. It is the highest level that blood pressure reaches when the heartbeats.

The second (lower) number is the diastolic blood pressure. It is the lowest level that blood pressure can reach as the heart slows down between beats.

Blood pressure readings:

Keep blood pressure low. Even if you do not have high blood pressure at this time, it is essential to keep your blood pressure as low as possible—the higher your blood pressure, the higher your risk of health problems.


For example, a blood pressure of 135 out of 85 may be “normal,” but someone with this reading is twice as likely to have a heart attack or stroke as someone with a reading of 115 out of 75.

What are thiazide diuretics?

A diuretic is a medication that increases the amount of water that leaves the kidneys, as it causes an increase in urine, called diuresis.

They are also used to treat or eliminate body fluids when the body accumulates too much liquid, such as heart failure.

 Examples of thiazide diuretics

There are a number of thiazide diuretics, which include: chlorthalidone, bendroflumethiazide, cyclopentiazide, xipamide, and indapamide.

How do thiazide diuretics work?

One of its effects is to make the kidneys lose more fluid. They do this by interfering with the transport of salt and water through specific cells in the kidneys.

Thiazide diuretics tend to have a weak action on the kidneys, so a significant increase in the urine is not observed if taken (compared to loop diuretics).

They also have the effect of widening (dilating) the blood vessels. A combination of these two effects reduces blood pressure.

Side effects of thiazide diuretics

Side effects are rare since the dose needed to lower blood pressure is low.

Common or severe side effects include:

  • A possible increase in your blood sugar level. Some people with diabetes may need more treatment to keep their blood sugar levels regular.
  • A possible increase in uric acid level is sometimes triggered when taking a diuretic.
  • The balance of salt in the bloodstream is sometimes altered, which can cause low levels of potassium, sodium, and magnesium and a high level of calcium. These effects can cause weakness, confusion, and, in rare cases, develop abnormal heart rhythms.

You may be recommended to have a blood test to check for these problems.

Other problems are:

  • Stomachache.
  • Dizziness when standing due to too-low blood pressure (hypotension).
  • Erection problems ( impotence ) are often reversible after stopping treatment.
  • Sensitivity of the skin to the ultraviolet rays of the sun.

Other considerations

Most thiazide diuretics are taken once a day in the morning or recommended by the treating physician. Any reduction in blood pressure is maintained for 24 hours with this dose once a day. However, the effect of passing extra urine disappears in 12 hours.

Therefore, you will not have to get up at night to make additional trips to the bathroom. The dose used to treat high blood pressure is relatively low, and many people hardly notice an increase in the amount of urine.