Headache, drowsiness, tiredness, weakness, blurred vision, nausea, vomiting, diarrhea, or constipation may occur as your body adjusts to the medication. If any of these effects persist or worsen, tell your doctor or pharmacist promptly.
Lightheadedness or dizziness upon standing may also occur, especially after the first dose and shortly after taking a dose of the drug during the first week of treatment. To reduce the risk of dizziness and fainting, get up slowly when rising from a seated or lying position. If dizziness occurs, sit or lie down immediately. Your dose may need to be adjusted.
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.
Tell your doctor immediately if any of these unlikely but serious side effects occur: pounding heartbeat, fainting, frequent urination, mental/mood changes (such as depression), swelling of the feet/ankles.
For males, in the very unlikely event you have a painful, prolonged erection (lasting more than 4 hours), stop using this drug and seek immediate medical attention, or permanent problems could occur.
A very serious allergic reaction to this drug is rare. However, seek immediate medical attention 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.
In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.