Diuretics for hypertension

Why are diuretics used to treat high blood pressure?

Diuretics are commonly known as ‘water pills’ and they are a medication that removes excess water and salt from the body. They can be used in the treatment of hypertension (high blood pressure) which can be a contributing factor in developing heart and circulation problems (cardiovascular disease).

Diuretics have proved to be effective in the prevention of stroke and heart attack in many people. Some foods and herbs will act as natural diuretics.

The diuretic medication increases the amount of sodium that is excreted in urine but different types of diuretic will affect different sections of the kidneys

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Types of diuretic medication

Thiazide diuretics

Thiazide diuretics are the most commonly used type when treating hypertension; there are several classes of thiazide diuretics; they are:

  • Bendroflumethiazide
  • Chlorthalidone
  • Cyclopenthiazide
  • Indapamide
  • Xipamide

Thiazide diuretics make the kidneys pass out more urine. This is achieved by interfering with the transport of salt and water across cells in the kidneys.  These diuretics have a mild effect on the kidneys so it is unlikely that there will be a huge change in the amount of urine passed when compared to the effect of loop diuretics. Combined with the increase in urine output, thiazide diuretics also cause widening of the blood vessels; the combination of these two effects results in a reduced volume of blood occupying a greater volume in the circulatory system. This will result in blood travelling around the body at reduced pressure.


Side effects of thiazide diuretics

Side effects of thiazide diuretics are dose related but when taking them for hypertension they are not common; this is related to the fact that only low doses of the medication are needed to treat hypertension.

Possible side effects include:

  • Increase in urination
  • Increase in blood sugar levels. This may be an issue if the patient is a diabetic and these people may need to medicate to reflect this.
  • Increased levels of uric acid in the bloodstream may cause problems for gout sufferers; uric acid is a contributory causal factor in gout attacks.
  • The balance of salts, that is, calcium, sodium, potassium and magnesium, may be disturbed resulting in low levels of sodium, potassium and magnesium and elevated levels of calcium.  There may be some problems as a result of the imbalance including weakness, confusion and heart arrhythmia (abnormal rhythm).  If taking these diuretics then blood tests may be needed to check the levels of salts.
  • Headaches
  • Irregular menstruation
  • Increased thirst
  • Sleeplessness
  • Lightheadedness
  • Impotence


Loop diuretics

Loop diuretics encourage urination by the kidneys; they block the reabsorption of sodium, potassium and chloride and so encouraging the excretion of urine.  The reduction in the volume of blood, in turn, results in a fall in blood pressure.

Loop diuretics are not the usual diuretic of choice in the treatment of hypertension but according to pub med, “Loop diuretics are not recommended in current hypertension guidelines largely due to the lack of outcome data. Nevertheless, they have been shown to lower blood pressure and to offer potential advantages over thiazide-type diuretics. Torsemide offers advantages of longer duration of action and once daily dosing (vs. furosemide and bumetanide) and more reliable bioavailability (vs. furosemide).”

Based on this it may be that they could be used more widely to treat hypertension. Currently, however, their major use is in the treatment of heart failure.


Side effects of loop diuretics

There are several side effects associated with loop diuretics:

  • Dizziness
  • Headache
  • Stomach upset
  • Dehydration
  • Low blood potassium levels (hypokalemia)
  • High serum levels of sodium (hypernatremia)


Potassium sparing diuretics

Potassium sparing diuretics are weak diuretics which are usually prescribed alongside another type of diuretic. They are useful in that while they encourage the body to lose fluid through increased urination this type of diabetic does not encourage the loss of potassium in the extra urine.


Side effects of potassium sparing diuretics

Potassium sparing diuretics tend to be given in small doses and so side effects are not common.  However, possible side effects vary according to which type of potassium sparing diuretic is being used.

Amiloride and triamterene

Usually, there are no side-effects but they can occur in some people. Possible side-effects include:

  • Tummy ache or cramp.
  • Dry mouth.
  • Feeling dizzy or faint, especially when getting up from sitting or lying positions (due to too low blood pressure).
  • Skin rash.
  • Feeling sleepy or confused.
  • Headache.
  • Aches and pains.
  • Muscle cramps.
  • Weakness.
  • Diarrhoea or constipation.
  • Potassium levels going too high (hyperkalaemia).

Spironolactone and eplerenone

Possible side-effects include:

  • Tummy upsets.
  • Feeling sick (nausea) or being sick (vomiting).
  • Sexual problems.
  • Enlargement of the breasts (both in men and women).
  • Irregular menstrual periods.
  • Confusion.
  • Dizziness.
  • Skin rash.
  • Excessive hair growth.
  • Liver problems.
  • High levels of potassium.



Diuretics are just one class of drug that is used to treat hypertension. Other types include:

  • Angiotensin-converting enzyme (ACE) inhibitors.
  • Angiotensin II receptor blockers (ARBs)
  • Diuretics.
  • Beta-blockers.
  • Calcium channel blockers.
  • Alpha-blockers.
  • Alpha-agonists.
  • Renin inhibitors.

Medication for hypertension may often be given alone or in combination with other drugs, however, in most cases, the first line of treatment in simple hypertension cases will be thiazide diuretics.

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