This medication is used to treat high blood pressure. Lowering high blood pressure helps prevent strokes, heart attacks, and kidney problems. Chlorothiazide is a "water pill" (diuretic) that causes you to make more urine. This helps your body get rid of extra salt and water.

This medication is also used to decrease swelling (edema) caused by conditions such as cancer, heart failure, liver disease, and kidney disease. This effect can help your kidneys work better and lessen symptoms such as trouble breathing and swelling in your ankles, feet, hands, or belly.

This section contains uses of this drug that are not listed in the approved professional labeling for the drug but that may be prescribed by your health care professional. Use this drug for a condition that is listed in this section only if it has been so prescribed by your health care professional.

This drug may also be used for a condition known as "water diabetes" (diabetes insipidus). It may also be used to reduce the risk of calcium kidney stones.

Take this medication by mouth with or without food as directed by your doctor, usually once or twice a day. If you take this drug too close to bedtime, you may need to wake up to urinate. It is best to take this medication at least 4 hours before your bedtime.

If you are using the liquid form of this medication, carefully measure the dose using a special measuring device/spoon. Do not use a household spoon because you may not get the correct dose. Shake the bottle well before each dose.

The dosage is based on your medical condition and response to treatment. Children's dosage is also based on age and weight.

Use this medication regularly to get the most benefit from it. To help you remember, take it at the same time(s) each day. Keep taking this medication even if you feel well. Most people with high blood pressure do not feel sick.

Cholestyramine and colestipol can decrease the absorption of chlorothiazide. If you are taking either of these drugs, take them at least 4 hours before or after taking chlorothiazide.

Tell your doctor if your condition does not get better or if it gets worse (for example, your blood pressure readings remain high or increase).

Dizziness, lightheadedness, headache, blurred vision, loss of appetite, stomach upset, diarrhea, or constipation may occur as your body adjusts to the medication. You may also experience decreased sexual ability. If any of these effects last or get worse, tell your doctor or pharmacist promptly.

To reduce the risk of dizziness and lightheadedness, get up slowly when rising from a sitting or lying position.

Remember that this medication has been prescribed because your doctor has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

This medication can cause dehydration and electrolyte imbalance. Tell your doctor right away if you have any symptoms of dehydration or electrolyte imbalance, including unusual dry mouth/thirst, muscle cramps/weakness, slow/fast/irregular heartbeat, or confusion.

Tell your doctor right away if you have any serious side effects, including:

• signs of liver problems (such as nausea/vomiting that doesn't stop, stomach/abdominal pain, yellowing eyes/skin, dark urine)
• signs of infection (such as sore throat that doesn't go away, fever, chills, cough)
• fainting
• joint pain (such as big toe pain)
• numbness/tingling of the arms/legs
• easy bruising/bleeding
• unusual tiredness
• signs of kidney problems (such as change in the amount of urine)

Get medical help right away if you have any very serious side effects, including:

• decrease in vision
• eye pain

A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including:

• rash
• itching/swelling (especially of the face/tongue/throat)
• severe dizziness
• trouble breathing

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US - Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Before taking chlorothiazide, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Before using this medication, tell your doctor or pharmacist your medical history, especially of:

• kidney disease
• liver disease
• untreated salt/mineral imbalance (such as imbalance of sodium, potassium, calcium, magnesium)
• dehydration
• gout
• lupus
• certain recent nerve surgery (sympathectomy)

If you have diabetes, chlorothiazide may affect your blood sugar. Check your blood sugar regularly as directed and share the results with your doctor. Tell your doctor right away if you have symptoms of high blood sugar such as increased thirst/urination. Your doctor may need to adjust your diabetes medication, exercise program, or diet.

This drug may make you dizzy or blur your vision. Alcohol or marijuana (cannabis) can make you more dizzy. Do not drive, use machinery, or do anything that needs alertness or clear vision until you can do it safely. Limit alcoholic beverages. Talk to your doctor if you are using marijuana (cannabis).

Severe sweating, diarrhea, or vomiting may cause dehydration and cause you to feel lightheaded. Tell your doctor if you have severe diarrhea or vomiting. To prevent dehydration, drink plenty of fluids unless your doctor tells you not to.

This drug may decrease your potassium levels. Ask your doctor about foods high in potassium (such as bananas, orange juice) or about using a salt substitute containing potassium. A potassium supplement may be prescribed by your doctor.

This medication may make you more sensitive to the sun. Limit your time in the sun. Avoid tanning booths and sunlamps. Use sunscreen and wear protective clothing when outdoors. Tell your doctor right away if you get sunburned or have skin blisters/redness.

Before having surgery, tell your doctor or dentist about all the products you use (such as prescription drugs, nonprescription drugs, and herbal products).

Older adults may be more sensitive to the side effects of this drug, especially dizziness.

During pregnancy, this medication should be used only when clearly needed. Discuss the risks and benefits with your doctor.

This drug passes into breast milk. Consult your doctor before breastfeeding.

See also How to Use section.

Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (such as prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor's approval.

Some products that may interact with this drug are:

• dofetilide
• lithium

Some products have ingredients that could raise your blood pressure or worsen your swelling. Tell your pharmacist what products you are using, and ask how to use them safely (especially cough-and-cold products, diet aids, or NSAIDs such as ibuprofen/naproxen).

This product may interfere with certain lab tests. Make sure lab personnel and all your doctors know you use this drug.

If someone has overdosed and has serious symptoms such as passing out or trouble breathing, call 911. Otherwise, call a poison control center right away. US residents can call 1-800-222-1222. Canada residents can call 1-844-764-7669. Symptoms of overdose may include: severe dizziness, severe weakness, fainting.

Do not share this medication with others.

Lifestyle changes that may help this medication work better include exercising, stopping smoking, and eating a low-cholesterol/low-fat diet. Consult your doctor for more details.

Lab and/or medical tests (such as potassium levels, kidney function) may be done while you are taking this medication. Keep all medical and lab appointments. Consult your doctor for more details.

Have your blood pressure checked regularly while taking this medication. Learn how to monitor your own blood pressure at home, and share the results with your doctor.

If you miss a dose, take it as soon as you remember. If it is near the time of the next dose, skip the missed dose. Take your next dose at the regular time. Do not double the dose to catch up.

Store at room temperature away from light and moisture. Do not store in the bathroom. Do not freeze the liquid form of this medication. Keep all medications away from children and pets.

Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer needed. Consult your pharmacist or local waste disposal company.