Varenicline is generally well tolerated by smokers.

Varenicline is a nicotine partial agonist that has some nicotine-like effects, but also blocks the effects of nicotine.  In several trials, its efficacy appears to be greater than that of NRT or bupropion (Fagerström & Hughes, in press).  The most common side effect is nausea (30-40%), sometimes with vomiting.  To minimize the risk or severity of nausea, varenicline is initiated at 0.5 mg daily doses, and then gradually escalated to the full therapeutic dose of 1.0 mg twice daily. In most smokers nausea resolves over the course of treatment. Varenicline may also cause insomnia and abnormal/vivid dreams. In long-term studies, <10% of patients have to stop varenicline due to adverse events (Williams et al., 2007) and serious adverse events are rare (Cahill et al., 2007).

There are a number of reports of psychiatric disturbances, including suicide, in smokers taking varenicline. Warnings have been issued by the US FDA, the Australian TGA, and the European EMEA. The US and Australian new warning states that "there have been reports of depressed mood, agitation, changes in behavior, suicidal ideation and suicide in patients attempting to quit smoking while taking Chantix/Champix", and "Because these events are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure." In a recent report (Stapleton et al., 2008), varenicline was reported to be effective and safe in routine treatment of tobacco dependence, in smokers with or without mental illness  Varenicline is excreted from the body entirely by the kidneys, so side effects may be expected to be greater if administered in full doses to smokers with severe kidney disease.

1. Fagerström K, Hughes J. Integrating varenicline into treatment for tobacco dependence. Neuropsychiatr Dis Treat, in press.
2. Williams KE, Reeves KR, Billing CB Jr, Pennington AM, Gong J. A double-blind study evaluating the long-term safety of varenicline for smoking cessation. Curr Med Res Opin, 2007; 23: 793-801.
3. Cahill K, Stead LF, Lancaster T. Nicotine receptor partial agonists for smoking cessation. Cochrane Database Syst Rev, 2007; (1): CD006103.
4. Stapleton JA, Watson L, Spirling LI, Smith R, Milbrandt A, Ratcliffe M, Sutherland G. Varenicline in the routine treatment of tobacco dependence: a pre-post comparison with nicotine replacement therapy and an evaluation in those with mental illness. Addiction, 2008; 103: 146-54.