Metolazone (Oral)

Metolazone is a diuretic pill useful in the treatment of high blood pressure and generalized edema, but patients should be aware that this medication can produce significant side effects.


Metolazone is a powerful medication in the thiazide family of diuretics. This drug is used to treat patients with high blood pressure. It is also useful in treating patients who have edema or fluid in the lungs as a result of kidney malfunction or congestive heart failure. It may also be used to treat those patients with edema from idiopathic causes.

Metolazone works by blocking the reabsorption of sodium electrolytes in the renal cortex. This causes significant dieresis in the patient. After taking a dose of this medication, the patient will notice the effects in about two hours. Maximum effect may take up to four hours. Patients should note that this drug will cause significant urine production. The drug should be taken before 6pm in the evening so that the patient's sleep is not interrupted by frequent visits to the restroom.

Those who are allergic to other thiazide diuretics should not use metolazone. This drug is related to sulfa antibiotics. Those who are allergic to sulfa drugs should not use metolazone. Metolazone is also known to interact with lithium. Dosage adjustments of lithium may also be required.

There are a number of medications that may require dosage adjustments if taken along with metolazone. Those who take blood thinners, non-steroidal anti-inflammatory drugs, insulin, digoxin, seizure medications, asthma medications, corticosteroids or Vitamin D should inform their physician as dosage adjustments may be needed.

Those with certain health conditions should use metolazone with caution. Those with gout may suffer an exacerbation when taking metolazone. People with diabetes may have to adjust their insulin while on metolazone. Metolazone may increase the severity of attacks in those with lupus. Those with parathyroid conditions may not be able to take metolazone.

Those who are pregnant or nursing should take this drug with extreme caution. Thiazide diuretics like metolazone are known to cross the placental barrier and cause hypokalemia, hyponatremia and hypotension in the fetus. The drug is also excreted in breast milk. It is best not to breastfeed while using this medication.

There can be some significant side effects while using metolazone. The most commonly reported side effect is dizziness. This usually occurs due to a rapid drop in blood pressure when first taking the drug. It often improves over time. Patients should use caution when driving while first taking this medication.

Metolazone is known to cause sensitivity to sunlight. Patients should avoid prolonged exposure to UV light, or they should use a sunblock when going out during the daylight hours.

Use of metolazone can lead to the patient developing very low levels of potassium. Often, doctors will prescribe a potassium supplement to be taken along with metolazone. Patients are advised to eat a diet rich in foods like bananas that contain significant amounts of potassium.

Conditions Treated

  • Hypertension
  • Generalized edema
  • Edema due to congestive heart failure
  • Edema due to kidney malfunction

Type Of Medication

  • Diuretic

Side Effects

Metolazone can cause an allergic reaction in some patients. This type of reaction may manifest itself as a skin rash, difficulty breathing and swelling of the eyes and lips. One severe skin reaction called the Stevens-Johnson Syndrome is known to occur on very rare occasions. Skin peeling and blistering should be reported to one's healthcare provider immediately.

The most common side effect of metolazone is dizziness. This usually occurs when the drug is first taken. The blood pressure may lower too quickly, and this leads to dizziness in some patients.

Headache, constipation and diarrhea also occur occasionally with the use of this medication. Dry mouth is a fairly common side effect that lessens as the drug is used over time.

Metolazone can cause certain electrolytes in the body to reach levels that produce side effects. Potassium and sodium levels in the body may be lowered significantly leading to dizziness, low blood pressure and arrhythmias.

In addition to the above mentioned side effects, the following side effects have been reported by those using metolazone:

  • Black stools


Metolazone is supplied as 2.5, 5 and 10-milligram tablets. The dosage is dependent on the condition being treated.

For high blood pressure, patients are started on a dose of 2.5 to 5 milligrams once per day. If needed, the dose can be gradually increased up to 20 milligrams once per day.

For the relief of edema, patients initially receive 2.5 to 10 milligrams once per day. This may be gradually increased to 20 milligrams per day if required for relief of edema.


Serious interactions may occur with metolazone and the following:

  • Aminolevulinic acid oral

Patients on these drugs may need dosage adjustments and should be watched for possible interactions:

  • Acebutolol

Many other drugs may cause some minor interactions, so patients should always inform their healthcare provider regarding the medications both prescription and nonprescription that they are taking.


Patients who are taking this medication should not be overexposed to UV light as this medication causes skin sensitivity. Patients should avoid prolonged exposure to the sun. If going outdoors, patients should use a good sunblock.

Pregnant women should not use this medication. Thiazide diuretics have been shown to cause possible fetal harm. The fetus could develop dangerously low potassium and sodium levels if this drug is taken by the mother. This medication also is excreted in breast milk. Women on this drug are advised against breastfeeding while using metolazone.

Patients with certain medical conditions should not use this medication as it may exacerbate those conditions. Gout, diabetes, lupus and parathyroid conditions may be made worse by metolazone.

Patients should be aware of the fact that metolazone may cause depletion of potassium and sodium in the body. Doctors may perform periodic blood tests to monitor the patient's electrolyte levels. Some patients may need to take prescription potassium supplements while taking metolazone.


Metolazone should be stored at room temperature. It should be kept in a dry place out of direct sunlight.


Metolazone is a diuretic drug used to treat high blood pressure and edema that occurs in the body due to congestive heart failure or idiopathic reasons. It is a powerful drug that produces effects in as little as two hours. It comes to peak effectiveness in up to four hours. Patients should note that significant amounts of urine will be produced. The medication should be taken before 6 pm to avoid frequent bathroom trips in the middle of the night.

Metolazone is known to interact with a number of medications. Patients taking drugs such as blood thinners, corticosteroids, insulin, non-steroidal anti-inflammatory drugs and lithium may need to have the dosage of those drugs modified during the time that they are using metolazone.

The most common side effect of metolazone is dizziness often brought on early in treatment by a rapid lowering of blood pressure. This usually goes away the longer a patient takes the medication.

The use of metolazone may cause a significant drop in potassium and calcium. Patients should eat potassium-rich foods like bananas while taking the medication.

Pregnant women should not use metolazone as its class of drugs is known to cause fetal harm. Mothers should not breast-feed while using this medication.