Champix Side Effects

Varenicline--also called Champix or Chantix--is a medication that is used to help smokers quit smoking. Champix works by binding to a nicotinic cell receptor, which blocks nicotine's ability to activate the dopamine system in the brain. The dopamine system produces the feeling of pleasure associated with smoking. Without this stimulation, the "reward" sensation associated with smoking does not occur, allowing smokers to potentially stop their dangerous habit. However, Champix is associated with a variety of side effects.

Psychiatric Effects

Potentially significant behavioral changes may occur from Champix use. While some of these changes are relatively mild--for instance, feeling more agitated than usual--others are significant, such as becoming depressed. In addition, suicidal thoughts and suicide have both been reported in Champix users. It is not yet clear exactly why these psychiatric changes occur. The Federal Drug Administration recommends that all patients taking Champix should be closely monitored by their physicians in order to be aware of any changes in behavior or mood, or suicidal thoughts.

Central Nervous System Side Effects

The online medical reference UpToDate reports that nearly 20 percent of Champix users may experience insomnia. Headaches are also quite common, impacting between 15 to 19 percent of users. Some people may experience the opposite sleep-related effects, such as sleepiness and lethargy. However, these effects are much more rare, affecting between 1 and 2 percent of patients. In addition, the varenicline product website reports that changes in dreaming are also possible; UpToDate indicates that between 9 and 13 percent of people taking varenicline report abnormal dreams.

Digestive System Side Effects

Nausea is one of the most common side effects of Champix; UpToDate reports that between 16 and 40 percent of users experience this effect. Vomiting is a less-common effect, occurring in less than 5 percent of Champix users. Other potential effects on the digestive system include gassiness, abdominal pain and constipation; these effects each occur in about 7 percent of people taking the medication. Some users may feel that their appetite has increased, while others may find that they have no appetite while taking Champix. Finally, about 5 percent of patients may have "indigestion," also known as dyspepsia.

Respiratory System Side Effects

About 1 to 2 percent of users experience shortness of breath while taking this medication. In addition, a runny nose--also called rhinorrhea--was also noted in about 1 percent of users. UpToDate reports that between 5 and 7 percent of users experience cough or shortness of breath symptoms as though they had a viral illness such as a cold.