Varenicline Adverse Effects
Varenicline commonly causes nausea (30% of patients), insomnia, abnormal dreams, headache, and fatigue, but does NOT increase serious neuropsychiatric events, cardiovascular events, or mortality compared to placebo. 122
Common Adverse Effects (Dose-Dependent)
The most frequent side effects with varenicline 1 mg twice daily include:
Nausea: Occurs in 30% of patients (vs 10% placebo), typically mild-to-moderate and transient, though can persist for months in some patients. Approximately 3% discontinue due to nausea. 12 For every 5 patients treated, expect 1 case of nausea. 3
Sleep disturbances:
Gastrointestinal effects:
Other common effects: Headache, fatigue (28% increased risk) 24
Serious Adverse Effects (Rare but Important)
Neuropsychiatric Events
Despite historical concerns, high-quality evidence shows NO increased risk of serious neuropsychiatric events. 14 The 2015 meta-analysis of 39 trials (10,761 participants) found no increased risk of:
- Suicide or suicide attempts (OR 1.67,95% CI 0.33-8.57)
- Suicidal ideation (OR 0.58,95% CI 0.28-1.20)
- Depression (OR 0.96,95% CI 0.75-1.22)
- Aggression, hostility, or irritability 4
The EAGLES trial confirmed no difference in moderate-to-severe neuropsychiatric events versus NRT or bupropion. 1 However, the FDA label still requires warning patients about potential mood changes, psychosis, hallucinations, and suicidal ideation—instruct patients to discontinue and contact you immediately if these occur. 22
Cardiovascular Events
No increased risk of major cardiovascular events (cardiovascular death, MI, stroke) was found across multiple systematic reviews. 1 One older 2011 meta-analysis suggested increased risk (OR 1.72), 6 but the 2021 USPSTF guideline analysis of larger datasets found no statistically significant difference in cardiovascular adverse events or major cardiovascular events. 1 Still, instruct patients to report new or worsening cardiovascular symptoms immediately. 2
Life-Threatening Reactions (Discontinue Immediately)
Angioedema: Swelling of face, mouth, tongue, neck, throat that can cause respiratory compromise. Discontinue immediately and seek emergency care. 222
Serious skin reactions: Stevens-Johnson syndrome and erythema multiforme reported. Stop at first sign of rash with mucosal lesions. 222
Seizures: Instruct patients to discontinue and contact you immediately if seizure occurs. Screen for seizure history before prescribing. 22
Somnambulism: Cases of sleepwalking with harmful behavior reported. Discontinue if occurs. 222
Other Serious Effects
Acute renal failure: Rare but reported, particularly in patients with preexisting renal insufficiency. Monitor renal function in patients with chronic kidney disease. 7
Altered alcohol tolerance: Advise patients to reduce alcohol consumption until they know how varenicline affects their tolerance. 22
Impaired driving/machinery operation: Caution patients about potential impairment. 22
Discontinuation Rates
Overall discontinuation due to adverse events: 12% for varenicline vs 10% for placebo. 2 Adverse effects cause nearly 1.5 times higher discontinuation rates (OR 1.47), which can reduce smoking cessation success. 8 The medication was generally well tolerated in recent trials, with only 2% discontinuing due to adverse events. 9
Clinical Management Pearls
For persistent nausea or insomnia: Consider dose reduction rather than discontinuation. 22 These effects are usually transient and the initial dose titration (0.5 mg daily for 3 days, then 0.5 mg twice daily for 4 days, then 1 mg twice daily) helps minimize nausea. 22
Take with food and full glass of water to reduce gastrointestinal effects. 22
Screen before prescribing: Ask about psychiatric history, seizure history, and renal function. Despite no increased neuropsychiatric risk in trials, some providers remain hesitant to prescribe in patients with schizophrenia or bipolar disorder. 10