Chantix (Varenicline) Side Effects: What to Know Before You Start

What is the most common side effect of varenicline?

Nausea is the most frequently reported side effect and the main reason people stop the medication early. The good news: it almost always improves after the first one to two weeks and is largely preventable with the right approach.

Strategies that help most people: - Take varenicline with a full glass of water - Take it with a full meal, not just a snack - Take the evening dose earlier rather than right before bed

Your clinician will typically start you at a lower dose and increase gradually over the first week. If nausea remains severe, there are adjustments that can help without stopping the medication entirely — tell your clinician rather than stopping on your own.

Does varenicline cause vivid dreams?

Yes — unusual or vivid dreams and some difficulty sleeping are recognized and fairly common side effects of varenicline. For most people this does not prevent completing the course, but for some it is disruptive enough to discuss timing with a clinician. Taking the medication earlier in the day rather than at night may reduce sleep-related effects. This side effect also tends to lessen over time.

What does the evidence actually show about mood and psychiatric risks?

Varenicline carried an FDA black-box warning about neuropsychiatric effects — depression, mood changes, agitation, suicidal thoughts — for roughly a decade, based on early post-market reports. This was a serious concern, particularly because smokers have higher background rates of depression and anxiety.

The EAGLES trial (Anthenelli et al., 2016) directly addressed this question in a large, carefully designed randomized study that compared varenicline, bupropion, a nicotine patch, and placebo in smokers both with and without psychiatric disorders 2Ref 2Anthenelli RM, Benowitz NL, West R, et al. (2016).Neuropsychiatric Safety and Efficacy of Varenicline, Bupropion, and Nicotine Patch in Smokers with and without Psychiatric Disorders (EAGLES): A Double-Blind, Randomised, Placebo-Controlled Clinical Trial.EAGLES trial findings: neuropsychiatric risk not meaningfully elevated vs placebo in people without psychiatric history; modest risk in those with psychiatric history; FDA revised black-box warning. Its findings showed that in people without a psychiatric history, the neuropsychiatric risk did not meaningfully exceed placebo. In people with a pre-existing psychiatric condition, there was a somewhat higher rate of neuropsychiatric events — though absolute numbers were small — and varenicline still outperformed other agents in helping people quit.

The FDA revised the black-box warning downward in 2016 based on this evidence. The current picture: neuropsychiatric risk is real but lower than initially feared, is concentrated in people with pre-existing mental health conditions, and must be weighed against the genuine and serious harms of continued smoking. This is a conversation to have with your clinician — not a reason to avoid discussing the medication.

Are there cardiovascular risks with varenicline?

Earlier data raised questions about whether varenicline increased the risk of cardiovascular events. Subsequent larger studies have not confirmed a meaningful increased risk in most people 1Ref 1Livingstone-Banks J, Fanshawe TR, Thomas KH, et al. (2023).Nicotine Receptor Partial Agonists for Smoking Cessation.Varenicline effectiveness for cessation; standard 12-week course; comparison to other agents. Anyone with recent unstable coronary artery disease or a recent heart attack should discuss this specifically with their clinician — this is part of the standard prescribing conversation.

It is worth noting: the cardiovascular benefit of quitting smoking is large and well established 3Ref 3Centers for Disease Control and Prevention (2023).Benefits of Quitting Smoking.Cardiovascular benefit of quitting smoking. For most people with heart disease, that benefit substantially outweighs the medication risk.

What other side effects should you know about?

Other commonly reported effects include headache, flatulence, dry mouth, and changes in taste. These are generally mild.

Alcohol: Some people report changes in alcohol tolerance or unusual behavior with drinking while on varenicline. Clinicians sometimes advise caution with alcohol during treatment.

Kidney disease: Varenicline is cleared by the kidneys. People with significant kidney impairment may need a dose adjustment managed by their prescribing clinician.

Drug interactions: Varenicline has few significant drug–drug interactions, but your clinician should review your full medication list as part of the prescribing visit.

How long do you take it and what if you relapse?

The standard course is 12 weeks. If you have successfully quit, some clinicians recommend an additional 12 weeks to reduce relapse risk 1Ref 1Livingstone-Banks J, Fanshawe TR, Thomas KH, et al. (2023).Nicotine Receptor Partial Agonists for Smoking Cessation.Varenicline effectiveness for cessation; standard 12-week course; comparison to other agents. A quit date is typically set about one to two weeks into treatment.

If you relapse during treatment, this does not mean the medication failed. Some people need additional support, a change in strategy, or a repeat course. Talk with your clinician rather than stopping abruptly without a plan.