Varenicline

Indications

• FDA-approved as an aid to smoking cessation treatment in adults, used together with behavioral support and a defined quit plan.
• Outperformed bupropion, nicotine patch and placebo for abstinence in the EAGLES trial, making it the preferred first-line agent.
• Combining varenicline with a nicotine patch raises abstinence rates further, an off-label strategy supported by randomized evidence.
• Off-label for smokeless tobacco cessation and for e-cigarette cessation, where a 2024 randomized trial showed benefit in young adults.
• Effective and neuropsychiatrically safe in people with stable psychiatric disorders, a group with high smoking-related mortality.
• The nasal spray marketed as Tyrvaya is the same molecule approved for dry eye disease and has no role in tobacco cessation.

Mechanism of action

• Partial agonist at the alpha4beta2 nicotinic acetylcholine receptor, the subtype that mediates nicotine reinforcement and withdrawal.
• Partial stimulation releases about half as much accumbens dopamine as nicotine, which relieves craving and withdrawal symptoms.
• Simultaneous receptor occupancy blocks nicotine binding, so cigarettes smoked during treatment deliver much less reward.
• Acts as a full agonist at alpha7 and alpha3beta4 nicotinic receptors, which may contribute to the prominent nausea.
• Has no monoamine reuptake activity, unlike bupropion, so it does not treat depression and does not lower seizure threshold much.

Pharmacokinetics

• Oral absorption is essentially complete with peak concentrations at 3-4 h, and food has no clinically meaningful effect on exposure.
• Undergoes minimal metabolism: roughly 92% of a dose is excreted unchanged in urine by filtration and active OCT2 secretion.
• Terminal half-life is about 24 h, so twice-daily dosing reaches steady state within four days of starting or changing the dose.
• No CYP450 metabolism and low protein binding under 20% mean essentially no pharmacokinetic interactions with psychotropics.
• Renal function is the sole clinically important determinant of exposure, driving dose reduction below a creatinine clearance of 30 mL/min.

Dosing

• Standard titration is 0.5 mg once daily on days 1-3, 0.5 mg twice daily on days 4-7, then 1 mg twice daily from day 8 for 12 weeks.
• Set the quit date for day 8, or use a flexible approach with quitting any time between weeks 2 and 5, or gradual reduction over 12 weeks.
• Successful quitters may continue an additional 12 weeks, for 24 weeks total, which measurably reduces late relapse.
• Take after eating with a full glass of water to limit nausea; if nausea persists, drop back to 0.5 mg twice daily rather than stopping.
• Creatinine clearance under 30 mL/min: maximum 0.5 mg twice daily; on hemodialysis the maximum is 0.5 mg once daily.
• No taper is needed at the end of treatment, though some patients report transient irritability when it is stopped abruptly.

Adverse effects

• Nausea affects roughly 30% of patients, is dose-related and usually mild to moderate; taking the dose after food reduces it substantially.
• Insomnia in about 18% and vivid or abnormal dreams in about 13% are the second-most common complaints and often persist.
• Headache, constipation, flatulence and dysgeusia occur; these rarely require discontinuation but do influence adherence.
• The neuropsychiatric boxed warning was removed in 2016 after the EAGLES trial found no excess of serious events versus placebo.
• Seizures occur rarely, in roughly 0.1%, usually in the first month; avoid or use cautiously in patients with a seizure disorder.
• Alcohol tolerance may fall, with reports of unusual or aggressive behavior and amnesia; advise reducing intake until tolerance is known.

Monitoring

• Baseline renal function with calculated creatinine clearance, since this is the only routinely required laboratory check.
• Ask about mood, agitation, hostility and suicidal ideation at follow-up despite removal of the boxed warning, particularly in psychiatric patients.
• Review nausea, sleep and dream disturbance at weeks 1 and 2, the period when most patients decide whether to continue.
• Track abstinence, cigarettes per day and craving; exhaled carbon monoxide is a simple objective confirmation when available.
• Recheck doses of clozapine, olanzapine and other CYP1A2 substrates within one to two weeks of the patient stopping smoking.

Interactions

• Essentially no cytochrome P450 interactions, which makes varenicline unusually easy to add to complex psychiatric regimens.
• Stopping smoking removes CYP1A2 induction and can nearly double clozapine, olanzapine, fluvoxamine, duloxetine, theophylline and caffeine levels.
• Cimetidine raises varenicline exposure by about 29% in severe renal impairment and warrants a dose reduction in that setting.
• Adding a nicotine patch increases nausea, headache, vomiting and dizziness even though the combination improves abstinence.
• Alcohol effects can be exaggerated, and case reports describe blackouts and aggression; counsel patients to limit intake.

Special populations

• Pregnancy: human data are limited, behavioral treatment is first-line, and nicotine replacement is generally preferred if pharmacotherapy is needed.
• Lactation: transfer into human milk has not been quantified; weigh the substantial benefit of quitting against uncertain infant exposure.
• Pediatric use is not FDA-approved under 18, although recent trial data support off-label use for vaping cessation in older adolescents.
• Geriatric patients need no special dose except as dictated by renal function, which commonly declines silently with age.
• Renal impairment drives all dose adjustment; no hepatic adjustment is required because hepatic metabolism is negligible.

Clinical pearls

• The neuropsychiatric boxed warning was removed in 2016; EAGLES found no signal versus placebo.
• Quitting smoking lifts CYP1A2 induction, so clozapine and olanzapine levels can nearly double.
• Nausea is dose-related: take after food, and drop to 0.5 mg BID rather than abandoning it.