See also Warning section.
Dizziness, tiredness, headache, stomach upset, or diarrhea may occur as your body adjusts to the medication. You may also experience increased sensitivity to the sun. If any of these effects persist or worsen, notify your doctor or pharmacist promptly.
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.
Infrequently, triamterene may cause a loss of too much body water (dehydration) and salt (minerals). Tell your doctor right away if you have any of these unlikely but serious symptoms of dehydration or mineral loss: very dry mouth, thirst, muscle cramps/weakness, fast/irregular heartbeat, nausea, vomiting, severe dizziness, unusual decrease in the amount of urine, fainting, confusion, seizures.
Tell your doctor right away if any of these unlikely but serious side effects occur: signs of a kidney stone (e.g., pain in the side/back/abdomen, painful urination, blood in the urine, fever, chills), joint pain (e.g., big toe pain).
Tell your doctor right away if any of these rare but very serious side effects occur: signs of infection (e.g., fever, persistent sore throat), easy bruising/bleeding, stomach/abdominal pain, persistent nausea/vomiting, unusual/persistent tiredness, yellowing eyes/skin, dark urine, unusual change in the amount of urine (not including the normal increase in urine when you first start this drug).
A very serious allergic reaction to this drug is unlikely, but seek immediate medical attention if it occurs. Symptoms of a serious allergic reaction may include: 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.