Varenicline and Champix Side Effects: What to Expect and How to Manage Them
The common and rare side effects of varenicline, practical tips to reduce them, and the warning signs to act on.
Part of the Access Doctor Stop Smoking Guide.
Key fact: Feeling sick is the most common side effect of varenicline, affecting up to about 1 in 3 people in clinical trials. It's usually mild, often eases after the first couple of weeks, and is less likely if you take your tablet after food with a full glass of water.
Varenicline, sold as Champix and as a generic, is one of the most effective prescription medicines for stopping smoking. Like all medicines it can cause side effects, although most people take it without major problems. Champix and generic varenicline contain the same medicine, so their side effects are the same. If you're thinking about starting it, our varenicline tablets page explains the course and prices.
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Order Varenicline →Common Side Effects
According to the product information, the side effects reported by more than 1 in 10 people are:
- Feeling sick (nausea)
- Headache
- Trouble sleeping and abnormal or vivid dreams
- Cold-like symptoms (a blocked or runny nose and sore throat)
Up to 1 in 10 people have increased appetite, weight gain, drowsiness, dizziness, changes in taste, wind, indigestion, constipation, diarrhoea, vomiting, dry mouth, rash, joint or back pain, or tiredness.
~1 in 3
People who felt sick in trials, usually mildly
1–2 wks
When most side effects start to settle
0.5mg
Twice-daily dose if 1mg isn't tolerated
Is It the Tablets or Nicotine Withdrawal?
Stopping smoking causes its own symptoms, and they overlap with varenicline's side effects. It isn't always possible to tell them apart, but this is a rough guide:
More likely the tablets
Feeling sick soon after a dose, vivid or unusual dreams, and changes in taste. These often start in the first week, before your quit date.
More likely withdrawal
Cravings, irritability, restlessness, poor concentration, increased appetite and a cough. These usually start after your quit date and ease over 2 to 4 weeks.
Poor sleep, headache and low mood can come from either. Our guide to nicotine withdrawal symptoms explains the withdrawal timeline. If you're not sure, ask your prescriber.
Champix Nausea: Why It Happens and How to Reduce It
Varenicline acts on nicotine receptors, including some in the gut and in the part of the brain that controls sickness. That's why feeling sick is its most common side effect. It's usually mild and doesn't stop most people finishing the course. In trials, only a small proportion stopped varenicline because of nausea.
1
Take it after food
Have your tablet after breakfast and after your evening meal. Food in your stomach cushions the effect, and the product information advises taking it after eating.
2
Drink a full glass of water
Swallow the tablet whole with a full glass of water, rather than a sip, so it doesn't sit in your throat or stomach.
3
Build up slowly
The starter pack increases your dose over the first week, which reduces sickness. Don't skip straight to the full dose.
4
Give it time
Sickness is most common in the first week or two and often eases as your body gets used to the medicine.
5
Ask about a lower dose or a switch
If sickness doesn't settle, your prescriber may lower your dose to 0.5mg twice a day. If it still doesn't settle, cytisinicline may be an option: see varenicline vs cytisinicline.
Vivid Dreams and Sleep Problems
Unusual, vivid or disturbing dreams and difficulty sleeping are common. They're thought to be linked to varenicline's effect on brain receptors involved in sleep. Many people find it helps to take the evening dose with their evening meal rather than at bedtime. Poor sleep is also a common symptom of nicotine withdrawal and usually improves after the first few weeks.
Mood Changes and Mental Health
When varenicline was first used, there were reports of depression, agitation, changes in behaviour and suicidal thoughts in people taking it. A large safety trial of more than 8,000 people, the EAGLES study, then found that varenicline didn't significantly increase serious mental health side effects compared with nicotine patches or a placebo, including in people with a history of mental illness.
Stopping smoking can affect mood whichever method you use, and it can make an existing mental health condition worse for a while. That's why your prescriber asks about your mental health before prescribing.
Stop taking varenicline and get help straight away if you feel agitated, depressed or unusually anxious, notice changes in your behaviour, or have thoughts of harming yourself. Contact your GP, NHS 111 or, in an emergency, call 999.
Rare but Serious Side Effects
Stop taking varenicline and get urgent medical help (999 or A&E) if you have:
- Swelling of the face, lips, tongue or throat, or difficulty breathing
- A severe skin reaction, such as a spreading rash, blistering or peeling
- Chest pain or new or worse heart symptoms
- A fit (seizure)
Report any suspected side effect to the MHRA through the Yellow Card scheme.
Alcohol, Driving and Other Medicines
- Alcohol: there have been reports of people on varenicline feeling more drunk than expected, or behaving unusually or aggressively after drinking. It hasn't been proven that varenicline caused this, but it's sensible to drink less while you take it.
- Driving: varenicline can cause dizziness, drowsiness and, rarely, brief loss of consciousness. Don't drive or use machines until you know how it affects you.
- Nicotine replacement: using NRT at the same time may add to nausea, headache, vomiting and dizziness.
- Other medicines: stopping smoking (rather than varenicline itself) can raise levels of theophylline, clozapine, olanzapine and warfarin, and change insulin needs. Tell your prescriber about everything you take.
Who Shouldn't Take Varenicline
- Under-18s
- Pregnant or breastfeeding women (nicotine replacement and NHS support are recommended instead)
- People with end-stage kidney disease
Tell your prescriber if you have a history of depression or other mental illness, epilepsy or seizures, heart or blood vessel disease, or kidney disease, so they can check varenicline is safe for you.
Stop Smoking · Rx
Varenicline Tablets
The generic form of Champix: a 12-week course. Starter pack from £30.99.
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Champix (Varenicline)
The original brand of varenicline, back in the UK since 2025.
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Complete a short online consultation and a UK pharmacist prescriber will check whether varenicline is safe for you.
Order Varenicline →Frequently Asked Questions
What are the most common side effects of Champix?
Feeling sick, headache, trouble sleeping, vivid dreams and cold-like symptoms are the most common, each affecting more than 1 in 10 people. Generic varenicline has the same side effects because it's the same medicine.
How long does Champix nausea last?
For most people it's worst in the first 1 to 2 weeks and then eases. Taking the tablet after food with a full glass of water helps. If it doesn't settle, your prescriber can lower your dose to 0.5mg twice a day.
Why does Champix give you weird dreams?
Varenicline acts on brain receptors that are involved in sleep, which can cause vivid or unusual dreams. Taking your evening dose with your evening meal rather than at bedtime may help.
Does varenicline cause depression?
A large study of over 8,000 people found no significant increase in serious mental health side effects with varenicline compared with nicotine patches or a placebo. Stopping smoking can affect mood with any method, so stop the tablets and get help if your mood changes.
Can I drink alcohol on Champix?
There have been reports of people feeling more drunk than expected or behaving unusually after drinking on varenicline. A direct link hasn't been proven, but it's best to drink less while you're taking it.
Does varenicline cause weight gain?
Increased appetite and weight gain are common, but mostly because stopping smoking itself increases appetite. Healthy snacks and regular activity help.
Can I stop taking varenicline if I get side effects?
You can stop at any time, but speak to your prescriber first unless the side effect is serious. They may be able to lower your dose or suggest cytisinicline instead, so you keep the benefit.
References
- Electronic Medicines Compendium. Champix (varenicline) film-coated tablets: Summary of Product Characteristics. medicines.org.uk
- NHS. Varenicline. nhs.uk
- Anthenelli RM, et al. The Lancet. Neuropsychiatric safety and efficacy of varenicline, bupropion, and nicotine patch in smokers with and without psychiatric disorders (EAGLES). 2016. doi.org
- NICE. Tobacco: preventing uptake, promoting quitting and treating dependence (NG209). nice.org.uk
- MHRA. Yellow Card scheme. yellowcard.mhra.gov.uk
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Prescription medicines require a consultation before they can be dispensed. Always consult a qualified healthcare professional for diagnosis and treatment. In a medical emergency, call 999.