9 Chantix Side Effects You Should Know About

Quitting smoking is far from easy, but it’s one of the best things you can do to improve your health if you’re a smoker. Chantix (varenicline) is one option to help you quit smoking. It’s a prescription medication you take by mouth twice a day.

Chantix side effects at a glance

Unlike nicotine replacement therapy (NRT) products to help you quit smoking, Chantix doesn’t contain nicotine. But there are still some Chantix side effects you should be aware of if you’re taking it.

Common side effects:

• Nausea

• Vivid or strange dreams (including nightmares)

• Constipation

• Gas

• Vomiting

• Headache

• Fatigue

• Trouble sleeping (insomnia)

• Dry mouth 

• Taste changes

Rare but serious side effects:

• Increased alcohol sensitivity

• Mood changes

• Serious skin reactions

• Accidental injury

• Sleepwalking

• Seizures

• Possible increased risk of heart attack

Below, we’ll review nine Chantix side effects in greater detail, and what to do if they happen to you.

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1. Nausea and vomiting

Nausea and vomiting are some of the most common Chantix side effects. Up to about 1 in 3 people taking Chantix during clinical trials experienced nausea. And up to 1 in 20 people reported vomiting. Experiencing nausea and vomiting is more likely with higher doses of Chantix.

In most cases, you’ll start with a low dose of Chantix and raise your dose slowly over the first week. This helps your body adjust to the medication and lowers the chance of nausea when taking it. You should take Chantix after eating or with a full glass of water. This can also help lessen nausea and vomiting.

If your symptoms are mild, you can often manage them at home. Try eating small meals and avoid spicy or greasy food. If you’re vomiting, make sure to stay hydrated. If your symptoms don’t go away or become severe, contact your healthcare team. They may suggest lowering your dose or switching to another treatment.

2. Insomnia and abnormal dreams

Chantix works by affecting nicotine receptors in the brain. This helps reduce nicotine cravings, but it can also cause unwanted brain-related side effects. These may include trouble sleeping and/or abnormal dreams in some people taking it. Rarely, Chantix may also cause sleepwalking. This could result in possible harm to yourself or others.

Once you’re finished with Chantix treatment, your sleep should return to normal. But if your symptoms become bothersome or you are sleepwalking, be sure to let your prescriber know. They may change your dose or stop the medication.

3. Constipation

Constipation is another common Chantix side effect. In studies, up to 1 in 12 people taking Chantix reported having constipation. Constipation tends to be one of the side effects you can treat at home, unless it becomes severe. Severe constipation is often associated with stomach pain, vomiting, and trouble eating. If this happens, seek medical care immediately.

Eating a high-fiber diet, drinking plenty of water, and getting regular exercise are helpful for both preventing and treating constipation. If you still have constipation that won’t go away, your care team may suggest using medications. Over-the-counter (OTC) medications for constipation include medications like docusate (Colace), senna (Senokot, Ex-Lax), and polyethylene glycol 3350 (Miralax).

OTC constipation medications should only be taken short term (for one week or less). If you find that you need these medications longer, check with your healthcare team. They can help decide on the best treatment option.

4. Gas and abdominal pain

Gas and abdominal pain are other stomach-related Chantix side effects. If you have a lot of gas while taking Chantix, there are a few things that can help. You can try avoiding foods that are more likely to cause gas, such as beans and broccoli. You can also take an OTC medication like simethicone (Gas-X), which helps break up gas bubbles in your system.

Abdominal pain can be a little more complicated. There are a lot of reasons you could have stomach pain. And you may not always know what’s causing it. If the cause is constipation or gas, then it could be related to Chantix. And you may be able to manage it at home. But if the pain isn’t going away, becomes worse, or is severe, it’s best to seek medical attention.

5. Alcohol sensitivity

Chantix may change the way your body responds to alcohol. You may feel more intoxicated than usual. And sometimes the combination may cause aggressive behavior and loss of memory.

It’s best to cut down or stop consuming alcohol while you’re taking Chantix. If you have questions or concerns about this, talk to your healthcare team for support.

If you or someone you know struggles with substance use, help is available. Call SAMHSA’s National Helpline at 1-800-662-4357 to learn about resources in your area.

6. Mood changes

You may have changes in your mood, including feeling depressed, anxious, or paranoid, while taking Chantix. But keep in mind that mood changes are also common when you stop smoking, as symptoms of nicotine withdrawal.

Regardless, it’s best to be aware of any changes in your mood when you’re taking Chantix. In fact, you should stop taking Chantix if you experience agitation, have a depressed mood, or behave in a way that’s not normal for you. As mentioned, it’s also best to avoid alcohol while taking Chantix, as it may make these symptoms worse.

In severe cases, people have reported aggression, hallucinations, and thoughts of suicide while taking Chantix. If you notice any of these symptoms, contact your prescriber right away.

If you or someone you know is having thoughts of suicide, you’re not alone, and help is available. Call the Suicide & Crisis Lifeline at 988, or text HOME to 741-741 to reach the Crisis Text Line.

7. Serious skin reactions

Some people have reported having serious skin reactions while taking Chantix. These include conditions like Stevens-Johnson syndrome and erythema multiforme. Both of these are rashes that are most often triggered by a new medication.

Skin reactions while taking Chantix are rare. But they can be life-threatening. If you notice an abnormal rash after starting Chantix, seek medical care immediately. These types of rashes require treatment in a hospital setting.

8. Accidental injury

You may have a higher risk of traffic accidents or other forms of accidental injury while taking Chantix. In some cases, patients taking Chantix reported feeling dizzy, tired, and having trouble concentrating. These symptoms can cause impairment when driving or operating machinery.

It’s a good idea to see how Chantix affects you before doing certain activities. This includes driving, operating machinery, or other activities that require you to be alert. If you feel Chantix is preventing you from participating in normal activities, be sure to talk to your healthcare team. They may change your dose or stop the medication.

9. Seizures

It’s not common, but there have been several reports of seizures in people taking Chantix. This is a rare side effect that’s usually seen in the first month of taking Chantix if it occurs.

If you have a history of seizures, or take medications that may increase the risk of seizures, Chantix may not be the best treatment option for you. So be sure your medical team knows your full health history. It’s also a good idea to give your prescriber and pharmacist a list of your medications, including OTC supplements. This will help them check for other medications that may increase your risk of seizures.

If you experience a seizure while taking Chantix, stop the medication and seek medical attention right away.

When should you seek medical care for Chantix side effects?

Your healthcare team (including your pharmacist) can help you navigate any side effects you experience from Chantix. Most will go away once you finish your treatment. But whether your symptoms are mild or severe, it’s always a good idea to keep your care team in the loop.

If you’re having symptoms like severe stomach pain, an abnormal rash, or mood changes, call your prescriber right away. If at any point your symptoms seem severe or life-threatening, seek emergency medical attention.

How to save on Chantix

There are ways to save on Chantix, which is available as a generic and brand-name medication. Anyone with a valid prescription, regardless of insurance status, can use GoodRx to purchase a box of brand-name Chantix at an exclusive cash price of $99. A box of the generic may cost as low as $37.30.

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Written by:

Austin Ulrich, PharmD, BCACP

​​Austin Ulrich, PharmD, BCACP, is a board-certified ambulatory care clinical pharmacist. Ulrich’s experience includes direct patient care in hospital and community pharmacies.

Edited by:

Stacia Woodcock, PharmD

Stacia Woodcock, PharmD, is a pharmacy editor for GoodRx. She earned her Doctor of Pharmacy degree from the University of Kentucky and is licensed in New York and Massachusetts.

Reviewed by:

Amy B. Gragnolati, PharmD, BCPS

Amy Gragnolati, PharmD, BCPS, is a pharmacy editor for GoodRx. Amy currently holds her pharmacist license in Georgia and California.

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