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Varenicline Uses: Side Effects & Warnings

Varenicline side effects can be bothersome and may include allergic reactions.  If you’re considering stopping varenicline because of these side effects, remember that finding the right treatment may take trial and error and some tweaking.

 It might seem like you don’t need the medication anymore, but if you stop taking it, the medicine will leave your body, and your symptoms might return. A medical study shows that 30% of patients taking varenicline experienced nausea as a side effect. Quitting without consulting your doctor can be life-threatening and can cause various side effects.

In a podcast, a mother and a daughter talk about their family’s struggles with addiction and mental health when the other daughter of the family gets addicted. They talk about the side effects of the medicines taken by her for treatment and how it’s important to handle these effects while giving support and setting limits. This guide will help you navigate the common, rare, and severe side effects that medicines like varenicline can have.

What is Varenicline?

Varenicline is a medication that helps people stop smoking. It is an oral drug that works by targeting specific receptors in the brain.

This is prescription-only and taken as a tablet once or twice daily. Varenicline was approved by the FDA in 2006. Since then, there have been serious concerns about its side effects on mood and behavior. In 2021, Pfizer stopped making the brand-name version of varenicline, called Chantix, because they found potentially cancer-causing chemicals in the medication during production. 

However, generic versions are still available because the benefits of the medication are believed to outweigh the risks.

How Does Varenicline Work?

Varenicline works through a specific mechanism in the brain to help people quit smoking. Here’s how it operates, step by step:

  1. Partial Stimulation of Receptors:

    • Varenicline partially stimulates the nicotinic acetylcholine receptors in the brain.
    • This partial activation helps reduce nicotine cravings and alleviates withdrawal symptoms by providing a moderate level of stimulation to these receptors.
  2. Blocking Nicotine:

    • Varenicline competes with nicotine by binding to the same nicotinic acetylcholine receptors.
    • By occupying these receptors, varenicline prevents nicotine from binding to them.
  3. Preventing Dopamine Release:

    • When nicotine binds to its receptors, it typically releases dopamine, a neurotransmitter associated with feelings of pleasure and satisfaction.
    • Varenicline blocks nicotine from binding to its receptors, thereby preventing the dopamine release that reinforces the habit of smoking.
  4. Decreasing Cravings and Withdrawal Symptoms:

    • By providing partial receptor stimulation, varenicline reduces the urge to smoke without delivering the full impact of nicotine.
    • It helps in managing withdrawal symptoms by maintaining some level of receptor activity.
  5. Binding to Specific Receptors:

    • Varenicline specifically targets the α4β2 nicotinic acetylcholine receptors..
    • By binding to these receptors at a lower level than nicotine, varenicline effectively decreases nicotine cravings and withdrawal symptoms, aiding individuals in their effort to quit smoking.

This action on the brain’s receptors helps reduce the dependence on nicotine, making it easier for individuals to stop smoking.

Use of Varenicline in treating Nicotine Addiction

Varenicline is primarily used to treat nicotine addiction, which is the compulsive craving for cigarettes despite wanting to quit. Nicotine, found in tobacco, temporarily produces pleasurable effects in the brain, leading to this addiction.

By blocking nicotine’s effects on the brain, varenicline helps reduce the craving and withdrawal symptoms that occur after quitting smoking. It also decreases the sense of satisfaction or enjoyment from smoking, making it easier for adults to quit.

Varenicline Side Effects: Common, Severe & Rare

A study shows that 12% of patients discontinued 1 mg of varenicline because of its side effects.

Among those who discontinued varenicline, more reported nausea 3%, insomnia 1.2%, and abnormal dreams 0.3% as the most common adverse events.

Common Varenicline Side Effects

Some varenicline side effects may improve as your body adjusts to the medication. However, if these symptoms persist or worsen over time, notify your healthcare provider immediately.

The most common adverse Varenicline side effects include: 

  • Heartburn
  • Dry mouth or unpleasant taste in the mouth
  • Insomnia
  • Nausea or vomiting
  • Changes in the menstrual cycle
  • Gas
  • Lack of energy
  • Joint or muscle pain
  • Abdominal pain
  • Constipation or diarrhea
  • Changes in appetite
  • Nightmares, abnormal dreams, or other sleep disturbances
  • Headache

If any of these symptoms persist, even temporarily, consult your prescribing doctor. Your dose may need to be adjusted.

Severe Varenicline Side Effects

Here are the severe physical varenicline side effects:

  • Chest pain, pressure, or squeezing
  • Difficulty speaking
  • Dizziness
  • Drowsiness
  • Hoarseness
  • Loss of consciousness
  • Numbness or weakness of the arms or legs
  • Pain in the arms, back, calves, neck, jaw, or stomach

Potential varenicline side effects include skin irritation, such as redness, swelling, blisters, peeling, and rashes. Some people may also experience swelling in areas such as the eyes, arms, ankles, face, or tongue. 

Severe reactions like mucosal lesions and angioedema (swelling under the skin) have also been reported.

Mental, Behavioral, and Emotional Side Effects

Severe mental, behavioral, and emotional Varenicline side effects include:  

  • Aggression or agitation
  • Anxiety
  • Changes in behavior or mood
  • Delusions
  • Depression
  • Hostility
  • Mania
  • Panic
  • Sleepwalking
  • Suicidal thoughts

Other neuropsychiatric adverse events observed:

  • Psychosis
  • Paranoia
  • Homicidal ideation
  • Suicidal ideation or actions

It’s crucial to monitor for these reactions and seek medical advice if any concerns arise while using Varenicline.

Varenicline Warnings

Some people have had severe side effects while taking varenicline to help them quit smoking, including:

Neuropsychiatric Adverse Events, Including Suicidality

Neuropsychiatric severe side effects have been reported in patients taking varenicline. These include changes in mood (such as depression and mania), psychosis, hallucinations, paranoia, delusions, thoughts of homicide, aggression, hostility, agitation, anxiety, and panic, as well as suicidal thoughts, suicide attempts, and completed suicides. 

While depression, including rare cases of suicidal thoughts, has been reported in those trying to quit smoking without medication, some adverse events have occurred in patients taking varenicline who continued to smoke.


Some people have had seizures while taking varenicline, both during clinical trials and after it was made available. This includes people with and without a history of seizures. Most seizures happened within the first month of starting the medication.

Patients should be advised to stop taking varenicline and contact their healthcare provider immediately if they have a seizure while on the medication.

Interaction with Alcohol

Some people have reported feeling more intoxicated by alcohol while taking varenicline. This sometimes led to unusual or aggressive behavior and memory loss. Patients should be advised to drink less alcohol while taking varenicline until they know how it affects them.

Accidental Injury

Some people taking varenicline have reported traffic accidents, near-misses, or other accidents. They experienced drowsiness, dizziness, loss of consciousness, or trouble concentrating. 


Some individuals taking varenicline have experienced somnambulism (sleepwalking), which can lead to harmful behavior towards themselves, others, or property. Patients should discontinue varenicline and seek medical advice if they experience sleepwalking.

Precautions while taking Varenicline

If any of these apply to you, talk to your doctor or other healthcare provider before taking varenicline.

  • Severe kidney problems or if you are receiving kidney dialysis (dose may need to be lowered)
  • Could be pregnant or are breast-feeding
  • Less than 18 years old

It’s crucial to use effective contraception if you’re of childbearing age and notify your healthcare provider about all medications you take, including insulin, theophylline, or blood thinners like warfarin, as they can interact with varenicline.

FAQs: Varenicline Side Effects

Que: What is the most severe side effect of varenicline?

Ans: Stop varenicline if you have serious side effects like seizures, symptoms of a heart attack (chest pain, shortness of breath, unusual sweating), or signs of a stroke (weakness on one side of the body, trouble speaking, sudden vision changes).

Que: What does varenicline do to the brain?

Ans: Varenicline, a prescription-only medication, binds selectively to α4β2 nicotinic cholinergic receptors in the brain. This action mediates dopamine release and is believed to play a significant role in nicotine addiction.

Que: What is varenicline suitable for? 

Ans: Varenicline is used to help people quit smoking when combined with education and counseling.

Que: Does varenicline cause weight gain? 

Ans: Varenicline was linked to a slight reduction in weight gain among smokers after they quit smoking.

Que: Who should not use varenicline?

Ans: Talk to your doctor before starting varenicline if you have severe kidney problems or if you are pregnant or breastfeeding. Varenicline is not recommended for individuals under 18 years old.


If you notice any of these symptoms while using varenicline, staying in close touch with your doctor is crucial. Before starting varenicline, make sure to have a heart-to-heart with your healthcare provider about your mental health history, especially if you’ve ever felt down or if quitting nicotine has made things tough for you.

And if you’ve got heart issues or start sleepwalking, reach out to your doctor right away. They may recommend stopping varenicline in these cases. Taking these steps helps ensure you’re safely managing any potential varenicline side effects.

Your health and well-being are top priorities.

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