SIDE EFFECTS: See also Warning and Precautions sections. Dizziness, lightheadedness, tiredness, nausea, and diarrhea may occur. If any of these effects persist or worsen, 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. This product may reduce blood flow to your hands and feet, causing them to feel cold. Smoking may worsen this effect. Dress warmly and avoid tobacco use. Remember that your doctor has prescribed this medication because he or she 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. The chlorthalidone in this product may cause a loss of too much body water (dehydration) and salt/minerals. Tell your doctor right away if you have any symptoms of dehydration or mineral loss, including: extreme thirst, very dry mouth, muscle cramps, weakness, fast/irregular heartbeat, confusion. Tell your doctor right away if you have any serious side effects, including: very slow heartbeat, fainting, trouble breathing, signs of kidney problems (such as change in the amount of urine), toe/joint pain, mental/mood changes (such as depression, mood swings), blue fingers/toes, new or worsening symptoms of heart failure (such as shortness of breath, swelling ankles/feet, unusual tiredness, unusual/sudden weight gain). 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.

PRECAUTIONS: Before taking this product, tell your doctor or pharmacist if you are allergic to atenolol or chlorthalidone; 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: liver disease, kidney disease, certain types of heart rhythm problems (such as a slow heartbeat, second- or third-degree atrioventricular block), gout, lupus, breathing problems (such as asthma, chronic bronchitis, emphysema), blood circulation problems (such as Raynaud's disease, peripheral vascular disease), untreated mineral imbalance (such as low potassium), serious allergic reactions including those needing treatment with epinephrine, a certain muscle/nerve disease (myasthenia gravis). This drug may make you dizzy. Alcohol or marijuana can make you more dizzy. Do not drive, use machinery, or do anything that needs alertness until you can do it safely. Limit alcoholic beverages. Talk to your doctor if you are using marijuana. Too much sweating, diarrhea, or vomiting may cause loss of too much body water (dehydration) and increase your risk of dizziness or lightheadedness. Report prolonged diarrhea or vomiting to your doctor. Be sure to drink enough fluids to prevent dehydration unless your doctor directs you otherwise. Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products). This medication may reduce the potassium levels in your blood. Ask your doctor about adding potassium to your diet. Your doctor may prescribe a potassium supplement. If you have diabetes, this product may mask the fast/pounding heartbeat you would usually feel when your blood sugar falls too low (hypoglycemia). Other symptoms of low blood sugar, such as dizziness and sweating, are unaffected by this drug. This product may also make it harder to control 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 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. Older adults may be more sensitive to the side effects of this drug, especially dizziness. Tell your doctor if you are pregnant or plan to become pregnant. You should not become pregnant while you are using this medication. Atenolol/chlorthalidone may harm an unborn baby. If you become pregnant while using this medication, talk to your doctor right away about its risks and benefits. Atenolol and chlorthalidone pass into breast milk. Atenolol may harm a nursing infant. Consult your doctor before breast-feeding.

DRUG INTERACTIONS: 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 (including 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 include: cisapride, dofetilide, dolasetron, fingolimod, lithium. Some products have ingredients that could raise your heart rate or blood pressure. 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 laboratory tests (including parathyroid, protein-bound iodide), possibly causing false test results. Make sure laboratory personnel and all your doctors know you use this drug.

OVERDOSE: 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 their local poison control center at 1-800-222-1222. Canada residents can call a provincial poison control center. Symptoms of overdose may include: severe dizziness, fainting, very slow heartbeat, trouble breathing.