This medication can cause high potassium levels (hyperkalemia). This effect is more likely to occur in older adults and in patients with kidney disease, diabetes, or a serious illness. Potassium levels must be closely monitored on a regular basis while taking this medication. If not treated, very high potassium levels can sometimes be fatal. Tell your doctor right away if you develop any symptoms of high potassium levels, including muscle weakness, slow/irregular heartbeat, numb/tingling skin.

Headache, dizziness, nausea, vomiting, loss of appetite, stomach/abdominal pain, gas, or diarrhea may occur. If any of these effects last or get worse, tell your doctor or pharmacist promptly. 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. When given with other diuretics, this medication may 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: fainting, signs of liver problems (such as nausea/vomiting that doesn't stop, yellowing eyes/skin, dark urine), signs of kidney problems (such as change in the amount of urine). 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.

Some products that may interact with this drug are: lithium, sodium phosphate products, other products that may increase potassium levels (such as eplerenone, tacrolimus, cyclosporine, birth control pills containing drospirenone, potassium-sparing diuretics like spironolactone/triamterene, ACE inhibitors like benazepril/captopril, angiotensin receptor antagonists like losartan/valsartan). Some products have ingredients that could raise your blood pressure or worsen your heart failure. 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 medication may interfere with certain lab tests (such as glucose tolerance testing), possibly causing false test results. Make sure lab personnel and all your doctors know you use this drug.