Like all medicines, this medicine can cause side effects, although not everybody gets them. Giving up smoking with or without treatment can cause various symptoms. These could include changes of mood (like feeling depressed, irritable, frustrated or anxious), sleeplessness, difficulty concentrating, decreased heart rate or increased appetite or weight gain. You should be aware of the possible emergence of serious neuropsychiatric symptoms, such as agitation, depressed mood, or changes in behaviour during a quit attempt with or without CHAMPIX. You should contact a doctor or pharmacist if you experience such symptoms. Serious side effects of either an uncommon or rare frequency have occurred in people attempting to quit smoking with CHAMPIX: seizure, stroke, heart attack, suicidal thoughts, loss of contact with reality and being unable to think or judge clearly (psychosis), changes in thinking or behaviour (such as aggression and abnormal behaviour). There have also been reports of severe skin reactions including Erythema Multiforme (a type of rash) and Stevens-Johnson Syndrome (a serious illness with blistering of the skin, mouth, around the eyes or genitals) and serious allergic reactions including angioedema (swelling of the face, mouth, or throat). Very common side effects which may affect more than 1 in 10 people include; inflammation of the nose and throat, abnormal dreams, difficulty sleeping, headache and nausea. For a full list of side effects, please click here to read the Patient Information leaflet.