How does this medication work? What will it do for me?

Chlorthalidone belongs to the group of medications called diuretics. It is also an antihypertensive. This medication is used to treat fluid retention (edema) occurring with congestive heart failure and disorders of the liver and kidney. It is also used alone or in combination with other medications to treat high blood pressure. Chlorthalidone works by making the body lose excess water and salt.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than the ones listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

What form(s) does this medication come in?

Each yellow, round, flat-faced, bevelled-edged, compressed tablet, scored and engraved "APO" over "100" on one side, contains chlorthalidone 100 mg. Nonmedicinal ingredients: colloidal silicon dioxide, D&C Yellow No. 10 Aluminum Lake, FD&C Yellow No. 6 Aluminum Lake, magnesium stearate, and microcrystalline cellulose.

How should I use this medication?

The usual recommended dose of chlorthalidone is 25 mg to 100 mg once daily or in divided doses.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones given here, do not change the way that you are taking the medication without consulting your doctor.

It is important to take this medication exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from light and moisture, and keep it out of the reach of children.

Do not dispose of medications in wastewater (e.g. down the sink or in the toilet) or in household garbage. Ask your pharmacist how to dispose of medications that are no longer needed or have expired.

Who should NOT take this medication?

Do not take chlorthalidone if you:

  • are allergic to chlorthalidone, sulfa drugs, thiazide drugs, or any of the ingredients of the medication
  • are unable to produce urine
  • have severe liver disorder

If the passage of urine continues to increase over time during treatment of severe progressive kidney disease, chlorthalidone should be stopped.

What side effects are possible with this medication?

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

  • decreased sexual ability
  • diarrhea
  • dizziness or lightheadedness, especially when getting up from a sitting or lying down position
  • headache
  • increased sensitivity of skin to sunlight
  • loss of appetite
  • nausea
  • upset stomach
  • vertigo (sensation of spinning)
  • vomiting

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not check with your doctor or seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

  • black, tarry stools
  • blood in urine or stools
  • cough or hoarseness
  • fever or chills
  • joint pain
  • lower back or side pain
  • painful or difficult urination
  • pinpoint red spots on skin
  • skin rash or hives
  • stomach pain (severe) with nausea and vomiting
  • unusual bleeding or bruising
  • yellow eyes or skin
  • Signs and symptoms of too much potassium loss:

  • dry mouth
  • increased thirst
  • irregular heartbeat
  • mood or mental changes
  • muscle cramps or pain
  • nausea or vomiting
  • unusual tiredness or weakness
  • weak pulse
  • Signs and symptoms of too much sodium loss:

  • confusion
  • convulsions
  • decreased mental activity
  • irritability
  • muscle cramps
  • unusual tiredness or weakness

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Are there any other precautions or warnings for this medication?

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Cholesterol: Increases in cholesterol and triglyceride levels may occur when you are taking chlorthalidone. Your doctor will monitor your cholesterol and triglyceride levels with blood tests while you are taking this medication.

Diabetes: Chlorthalidone may make it more difficult for people with diabetes to control their blood sugar. If you have diabetes, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Dizziness/slower reaction: Because dizziness and a slower reaction time are possible side effects of taking chlorthalidone, especially at the start of therapy, you should see how the medication affects you before operating machines or driving motor vehicles.

Fluid and electrolyte balance: The levels of electrolytes in your body such as potassium, sodium, magnesium, and chloride can be reduced by the use of chlorthalidone. Your doctor will periodically check to see whether these are in balance, and a potassium supplement may be necessary. Warning signs or symptoms of fluid and electrolyte imbalance include:

  • confusion
  • drowsiness
  • dryness of mouth
  • lethargy
  • low blood pressure
  • muscle pains or cramps
  • muscular fatigue
  • nausea and vomiting
  • racing heartbeat
  • restlessness
  • seizures
  • thirst
  • weakness

If you experience any of these symptoms, contact your doctor. To prevent low potassium levels, eat foods that are high in potassium (e.g., bananas, dried figs, dates, prunes, nuts). If your potassium level is low, your doctor may suggest a potassium supplement.

Gout: This medication may aggravate or cause gout. People with high levels of uric acid in the blood or a history of gout should discuss with their doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Kidney disease: If you have reduced kidney function, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Liver disease: If you have reduced liver function or progressive liver disease, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Lupus: This medication may worsen or activate the symptoms of lupus. If you experience swollen and painful joints, fever, fatigue, or rash on the nose and cheeks while taking this medication, contact your doctor.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: This medication passes into breast milk. If you are a breast-feeding mother and are taking chlorthalidone, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using this medication have not been established for children.

What other drugs could interact with this medication?

There may be an interaction between chlorthalidone and any of the following:

  • alcohol
  • allopurinol
  • anesthetics
  • barbiturates (e.g., phenobarbital)
  • calcium supplements
  • cholestyramine
  • colestipol
  • corticosteroids (e.g., prednisone)
  • digoxin
  • insulin
  • lithium
  • medications that reduce potassium levels (e.g., other diuretics such as furosemide)
  • narcotics (e.g., codeine)
  • nonsteroidal anti-inflammatory medications (NSAIDs; e.g., ibuprofen, naproxen)
  • norepinephrine
  • oral diabetes medications (e.g., glyburide, gliclazide, metformin, pioglitazone)
  • other high blood pressure medications (e.g., beta-blockers)
  • quinidine
  • rituximab
  • tetracyclines (e.g., tetracycline, minocycline, doxycycline)
  • topiramate
If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:
  • stop taking one of the medications,
  • change one of the medications to another,
  • change how you are taking one or both of the medications, or
  • leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.