Common side effects
The most common side effect is nausea, affecting about three out of 10 people. This might be eased by taking Champix (varenicline) with food, or your doctor may recommend reducing your dose. Nausea is usually mild to moderate and fades with time. Other side effects include stomach or bowel problems (e.g. constipation, gas, dry mouth, vomiting, indigestion), headache, dizziness, sleeping problems, unusual dreams, feeling tired, increased appetite and changes in taste. They are usually mild and they generally appear in the first week of taking the medicine. Champix may cause other less common side effects. Talk to your doctor or pharmacist if you have any symptoms that concern you.
Serious side effects
Serious side effects related to Champix are uncommon and very serious side effects are rare. Symptoms of serious side effects are listed in the Consumer Medicine Information (CMI). If you have any of these symptoms, you need to tell your doctor as soon as possible. For very serious side effects, stop taking varenicline and go to hospital.
Some people have reported changes in mood or behaviour when they start taking Champix, usually within the first few weeks. These may include depression, agitation, aggression, thoughts of self harm, self harm, thinking about suicide, suicidal behaviour and hallucinations (seeing, hearing or sensing things that are not there). If you have any symptoms that concern you, you should stop taking Champix and seek medical advice as soon as possible
Symptoms can occur in people with no known history of mental illness. You should let family members and close friends know that you are taking Champix and ask them to be alert for unusual changes in your behaviour or mood. Several people who have experienced unexpected behaviour changes also reported having sleep disorders, especially nightmares, from the beginning of Champix use. Although, it should be noted that having abnormal dreams is a common side effect of varenicline, while the risk of serious behavioural changes is low. Champix may worsen symptoms in people with certain types of mental illness, so it is important to discuss your history with your doctor before taking varenicline.
It has been difficult for researchers to prove whether Champix is a cause of these mood and behaviour symptoms, as they are not common and some symptoms may also be due to nicotine withdrawal. Also, people who smoke have two to three times the risk of suicide compared to nonsmokers.
One study found that there may be a small increased risk for heart attack or stroke in people with heart or cardiovascular disease when using Champix, however this link has not been confirmed.
The risk of serious side effects in Champix users is low. For example, across 17 studies, 3.2% (32 in 1000) participants using Champix reported serious health problems that required medical attention, while 2.4% (24 in 1000) participants in the group not taking Champix had serious health problems. This research suggests that the risk of serious side effects among Champix users may be one-third higher than in those not using the drug
The risk of serious side effects may be higher in people already affected by certain illnesses. A possible link between varenicline and serious mental health and cardiovascular problems, while not proven, cannot be ruled out. If you have a history of mental illness, or of any other illness listed under What should I tell my doctor?, you need to discuss the risks and benefits of Champix with your doctor before you decide whether to use it. Family and carers of any person using Champix should be alert to mood and behaviour changes (read Side effects above).
Champix may make some people dizzy or sleepy. You need to know how it affects you before you drive a car, operate machinery, or do anything else that could be dangerous. In the United States, workers such as pilots and truck drivers are banned from using this medicine.
It is important to use Champix correctly, with your doctor’s supervision. Read the Consumer Medicine Information carefully and keep it until you’ve finished using the medicine. Never use any medication that has been prescribed for somebody else.
Taking too many tablets of Champix can cause serious side effects. If you think that you or someone else may have overdosed, immediately call your doctor or the Poisons Information Centre (13 11 26) for advice, even if there does not appear to be any effects. Or, go to hospital. Keep varenicline out of reach of children.