What is a Diuretic? Uses, Warnings, Side Effects

Diuretics are a class of medicines which are often prescribed to treat high blood pressure. These medications which are popularly known as water pills help the kidneys to increase the amount of water and salt in the urine and thereby clear extra fluid out of the body. This helps in bringing down blood pressure and reducing the risk of heart failure.

Diuretics may also be recommended to prevent or treat the symptoms in people who have conditions like congestive heart failure, liver failure, oedema (tissue swelling) and kidney disorders like kidney stones. In congestive heart failure, the heart cannot pump blood effectively throughout the body and this may lead to fluid buildup in the body causing oedema. Diuretics may reduce fluid buildup and help the heart function properly.

Types of Diuretics

There are three types of diuretic medicines and all of them excrete more fluids from the body in the form of urine. These are termed thiazide, loop and potassium-sparing diuretics. Each type of diuretic affects a different part of the kidneys. In some medication treatments, doctors may combine more than one type of diuretic or a diuretic with another blood pressure medication.

Thiazide Diuretics

Thiazide diuretics are the most frequently prescribed diuretics for high blood pressure. They decrease fluids in the body and also help blood vessels to relax. Sometimes, doctors may also prescribe thiazide with other medicines to lower blood pressure.

Examples of thiazide diuretics include −

  • Chlorothiazide

  • Chlorthalidone

  • Hydrochlorothiazide

  • Indapamide

  • Metolazone

Loop Diuretics

Loop diuretics have an effect on the loop of Henle which is a part of our kidneys to remove salt and excess water from the body. They are often used to treat heart failure.

Examples of loop diuretics include −

  • Bumetanide

  • Ethacrynic acid

  • Furosemide

  • Torsemide

Potassium-sparing Diuretics

These diuretics decrease fluid levels in the body without causing the body to lose potassium. The other types of diuretics may make the body lose potassium and this may lead to health problems like arrhythmia. Potassium-sparing diuretics may be prescribed for people who are at risk of low potassium levels. As these diuretics don't lower blood pressure similar to thiazide and loop diuretics, they are generally combined with another blood pressure medicine for better results.

Examples of potassium-sparing diuretics include −

  • Amiloride

  • Eplerenone

  • Spironolactone

  • Triamterene

Some herbs and plants like hawthorn, green and black tea and parsley are considered natural diuretics. Nevertheless, these herbs or plants may not replace a prescription diuretic.

Uses of Diuretics

Diuretic medications are prescribed by doctors to mainly treat high blood pressure. However, these medicines which can be consumed orally in the form of pills may also be used to treat, prevent or improve symptoms of conditions like heart failure, pulmonary oedema, renal failure, cardiomyopathy, ascites, diabetes insipidus, nephrotic syndrome and high intracranial or intraocular pressure.

Diuretics typically start working an hour or two after they are consumed and help the body dispose of extra fluid and salt as urine. People generally take diuretics by swallowing diuretic pills, but the doctor may give some diuretics through an intravenous (IV) in the arm if the patient is hospitalized.

Mostly diuretics provide good results even in older people and may be taken without getting serious problems or side effects. However, understanding certain precautions and side effects of diuretics may help users avoid any health complications.

Diuretics: Precautions and Warnings

Diuretics may cause dehydration or constipation if enough fluids are not consumed and hence, it is advised not to take any type of diuretic if a person has dehydration, electrolyte abnormality or lack of urine production (anuria). People having gout should avoid taking loop or thiazide diuretics. Furthermore, if someone has conditions like low potassium levels (hypokalemia), low sodium levels (hyponatremia) or low urine output (oliguria), one must avoid taking loop diuretics.

Similarly, potassium-sparing diuretics should not be taken if a person has high potassium levels or a condition like advanced kidney failure. In the case of chronic kidney disease, one must refrain from consuming thiazide diuretics and instead take loop diuretics.

Additionally, the doctor should periodically assess the urine output, electrolyte level, body weight and blood pressure of the person who is consuming diuretics. If the patients are senior citizens and have other cardiovascular, liver, metabolic or kidney disorders, doctors must always check their vitals from time to time if they are on diuretics.

The use of diuretics must be immediately discontinued if even after consuming them, there is no increase in urine output. Doctors must check for an underlying kidney disorder which could have been undiagnosed.

One must always consult a doctor before taking diuretics if the person is pregnant or breastfeeding. Also, if someone despite the person’s age has problems with the kidneys or liver, it is advised to take a doctor’s advice before taking diuretics.

Side Effects of Diuretics

The more common side effects of diuretics may include too little or too much potassium in the blood in the case of consuming potassium-sparing diuretics. Moreover, other side effects of diuretics may be low sodium levels, headache, dizziness, thirst, increased blood sugar, muscle cramps, increased cholesterol, skin rash, gout or diarrhoea. In rare cases, diuretics may also cause serious side effects like severe allergic reactions, kidney failure or irregular heartbeat (palpitations).

In addition to the above-mentioned side effects, sometimes diuretics may cause impotence, digestive problems, anaemia, tiredness, an increase in the frequency of urination, higher blood pressure in diabetics and unbalanced electrolytes. Non-steroidal anti-inflammatory drugs (NSAIDs) can affect kidneys when used at the same time with a loop or thiazide diuretics and may lead to acute kidney failure.

Loop diuretics when consumed with aminoglycoside antibiotics or some other drugs may cause hearing or balancing issues. When bendroflumethiazide (a thiazide diuretic) is taken with calcium supplements or vitamin D, it may cause calcium retention. Some medicines that might interact with a diuretic are cyclosporine (Restasis), antidepressants such as fluoxetine (Prozac) and venlafaxine (Effexor XR), lithium, digoxin (Digox) and other drugs for high blood pressure.


Diuretics are usually safe, but there are some risks if someone has other medical conditions or takes certain medications. Ideally, no medicine should be taken except doctor's approval and if someone has conditions like diabetes, pancreatitis, lupus, gout, menstrual problems, kidney problems, low or high potassium levels or frequent dehydration, one must consult a doctor before taking any type of diuretic.