What happens when you take smoking with varenicline?
Varenicline, sold as Chantix in the United States and Champix elsewhere, is a partial agonist at the alpha4-beta2 nicotinic acetylcholine receptor — the receptor subtype most responsible for nicotine's rewarding effects in the brain. Here is what happens, step by step:
- Varenicline occupies the receptor. It binds the alpha4-beta2 nicotinic receptor and stimulates it weakly, providing partial relief from craving and withdrawal even before you stop smoking.
- Nicotine from cigarettes is blocked. Because varenicline is sitting on the receptor, nicotine inhaled from a cigarette cannot bind as fully and produce its usual rewarding spike. Smoking becomes less satisfying.
- You start it before your quit date. Varenicline is begun a week or two before your target quit date, and you keep smoking during this lead-in. Many people find their interest in cigarettes fades on its own before the quit date arrives.
- Adding nicotine replacement amplifies side effects. Combining varenicline with a nicotine patch, gum, or lozenge is sometimes done to improve quit rates, but it increases common side effects — nausea, headache, vomiting, dizziness, indigestion, and fatigue — and more people stop treatment because of them.
This is not a dangerous drug-drug toxicity. It is a pharmacologic interaction with continued smoking and with added nicotine that shapes how the medicine feels and how well it is tolerated.
Why is this important?
Varenicline is one of the most effective smoking-cessation medications available. Reviews consistently show it outperforms placebo and works at least as well as, or better than, other single-agent options for achieving sustained abstinence. Using it well — understanding the lead-in smoking period and the trade-off of adding nicotine replacement — can be the difference between a successful quit attempt and stopping early.
Nausea is the most common side effect, and for some people it is the reason they discontinue. Continued heavy smoking during the early weeks can add to it, because smoking itself can cause nausea independent of the drug. Taking varenicline with food and a full glass of water helps.
The Chantix label historically carried a boxed warning for neuropsychiatric effects. That boxed warning was removed in 2016 after the large EAGLES trial found no significant increase in serious neuropsychiatric events compared with placebo, the nicotine patch, or bupropion. The label still notes that some people experience changes in mood, agitation, unusual or vivid dreams, and rarely thoughts of self-harm — these should be reported promptly. Less common but serious risks include seizures (especially with a seizure history), cardiovascular events in people with established heart disease, sleepwalking and other sleep behaviors, and rare reports of impaired driving.
What should you do?
Before you change anything: Talk with your prescriber about your quit date and whether nicotine replacement will be added. Do not start, stop, or combine smoking-cessation products on your own — your doctor or pharmacist can set up the schedule and dose that fit you.
Every day while on treatment: Take each dose with food and a full glass of water to limit nausea — avoid dosing on an empty stomach. Expect to keep smoking during the first week or two; by your quit date the rewarding effect of cigarettes should be substantially blunted. Don't be discouraged if cessation doesn't feel instant.
After a change (adding NRT, increasing dose, or quitting): If a nicotine patch or other replacement is added, expect more nausea and headache. Some people tolerate the combination well; others find it intolerable. There is no danger in stopping the combination if needed, but talk to your prescriber rather than stopping silently. Watch for and report severe depression, suicidal thoughts, agitation, hostility, or psychosis. Seek immediate care for seizures, angioedema, or severe skin reactions. Use caution driving or operating machinery until you know how varenicline affects you.
Which specific products are affected?
This interaction is specific to varenicline, sold as Chantix in the United States and Champix in many other countries, and now also available as generic varenicline tartrate tablets. It is typically taken as a roughly 12-week course that can be extended for people who have quit successfully and want to consolidate their abstinence.
On the smoking side, this applies to all combustible tobacco — cigarettes, cigars, pipes, and roll-your-own — and in concept to nicotine-containing e-cigarettes and vapes. The same tolerability trade-off applies to nicotine replacement therapies that might be combined with varenicline: patches (NicoDerm CQ), gum (Nicorette), lozenges, the inhaler, and nasal spray.
Bupropion (Zyban, Wellbutrin) is the other major cessation medication and is sometimes combined with varenicline in specialist settings for a modest improvement in quit rates at the cost of more side effects. Any combination cessation therapy should be individualized and guided by an experienced clinician.
The science behind it
The FDA Chantix (varenicline) prescribing information describes the mechanism — partial agonism at the alpha4-beta2 nicotinic receptor — and reports that co-administering varenicline with transdermal nicotine did not meaningfully change nicotine pharmacokinetics, but the combination produced more nausea, headache, vomiting, dizziness, indigestion, and fatigue than nicotine replacement alone, with a higher rate of discontinuation due to side effects.
The U.S. Department of Veterans Affairs patient guide on varenicline confirms the practical pattern: it is a partial nicotinic agonist, started a week or two before the quit date, with nausea as a common and expected side effect.
The RxList Chantix monograph echoes the mechanism and the tolerability of the nicotine-replacement combination. Together these sources support the direction and the moderate severity of this interaction.
Frequently Asked Questions
Is it dangerous to keep smoking after I start varenicline?
No. You are meant to keep smoking during the first week or two while the drug builds up before your quit date. Smoking on varenicline simply feels less rewarding, which is how it helps.
Why does varenicline make me feel nauseous?
Nausea is the most common side effect. Taking each dose with food and a full glass of water, and avoiding an empty stomach, usually makes it manageable. Tell your prescriber if it is severe.
Can I use a nicotine patch at the same time?
Sometimes, to improve quit rates — but it increases side effects like nausea and headache and makes some people stop treatment. Decide this with your prescriber rather than adding it yourself.
Does varenicline cause mood changes or suicidal thoughts?
The boxed warning for neuropsychiatric effects was removed in 2016 after a large trial found no significant increase in serious events. Some people still notice mood changes, agitation, or vivid dreams; report severe symptoms or thoughts of self-harm to your prescriber immediately.
How long do I take it?
It is usually a course of about 12 weeks, which your doctor may extend if you have quit successfully and want to consolidate. Follow the schedule your prescriber sets.
What should make me seek urgent care?
Seizures, severe mood changes or suicidal thoughts, allergic reactions including facial swelling (angioedema), or severe skin reactions warrant immediate medical attention.
Key takeaways
- Varenicline partially activates the same brain receptors nicotine targets, dulling cigarette satisfaction and easing withdrawal.
- Keeping smoking during the first week or two is expected and not dangerous — you start the drug before your quit date.
- Combining it with nicotine replacement can raise quit rates but increases nausea, headache, and discontinuation.
- Take each dose with food and water to limit nausea.
- Report severe mood changes, suicidal thoughts, or seizures urgently, and set your quit plan with your doctor or pharmacist.