Get emergency medical help if you have signs of an allergic reaction (hives, difficult breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning eyes, skin pain, red or purple skin rash with blistering and peeling).
Stop using varenicline and call your doctor at once if you have:
a seizure (convulsions);
thoughts about suicide or hurting yourself;
strange dreams, sleepwalking, trouble sleeping;
new or worsening mental health problems--mood or behavior changes, depression, agitation, hostility, aggression;
heart attack symptoms--chest pain or pressure, pain spreading to your jaw or shoulder, nausea, sweating; o
stroke symptoms--sudden numbness or weakness (especially on one side of the body), slurred speech, problems with vision or balance.
Your family or other caregivers should also be alert to changes in your mood or behavior.
Common side effects may include:
nausea (may persist for several months), vomiting;
constipation, gas;
sleep problems (insomnia); or
unusual dreams.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
 Varenicline side effects (more detail)
