See also Precautions section.
Nausea, headache, vomiting, drowsiness, gas, constipation, trouble sleeping, unusual dreams, or changes in taste may occur. If any of these effects last or get worse, tell 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.
Tell your doctor right away if you have any serious side effects, including: burning feeling in feet/toes, unusual pain in the legs when walking.
Stop taking varenicline and get medical help right away if you have any very serious side effects, including: seizure, symptoms of a heart attack (such as chest/jaw/left arm pain, shortness of breath, unusual sweating), signs of a stroke (such as weakness on one side of the body, trouble speaking, sudden vision changes, confusion), harmful behavior to self/others/property.
Rarely, varenicline may cause serious mental/mood changes, even after stopping the medication. Drinking alcohol while taking this medication may increase the risk for mental/mood changes. Quitting smoking itself may also cause mental/mood changes. Stop taking varenicline and tell your doctor or pharmacist right away if you have symptoms such as depression/suicidal thoughts, agitation, aggression, or other unusual thoughts or behavior.
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.