What the label lists and what reports show
Varenicline side effects
Varenicline's FDA label: “In the placebo-controlled premarketing studies, the most common adverse events associated with CHANTIX (>5% and twice the rate seen in placebo-treated patients) were nausea, abnormal (vivid, unusual, or strange) dreams, constipation, flatulence, and vomiting.” FAERS holds 79,556 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is nausea (14,464 reports).
- Generic listed
Check it at the source: the varenicline FDA label on DailyMed (effective January 23, 2026, Pfizer Laboratories Div Pfizer Inc); the FDA FAERS public dashboard.
What does the patient leaflet say about side effects?
From the patient leaflet: What are the possible side effects of CHANTIX?Serious side effects of CHANTIX may include: • See " What is the most important information I should know about CHANTIX? " • Seizures. Some people have had seizures during treatment with CHANTIX. In most cases, the seizures have happened during the first month of treatment with CHANTIX. If you have a seizure during treatment with CHANTIX, stop taking CHANTIX and contact your healthcare provider right away. • New or worse heart or blood vessel (cardiovascular) problems, mostly in people, who already have cardiovascular problems. Tell your healthcare provider if you have any changes in symptoms during treatment with CHANTIX. […]
Source: FDA drug label, NDA021928 (Pf Prism Cv), as published by Pfizer Laboratories Div Pfizer Inc, effective January 23, 2026 (SPL set f0ff4f27-5185-4881-a749-c6b7a0ca5696), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsIn the placebo-controlled premarketing studies, the most common adverse events associated with CHANTIX (>5% and twice the rate seen in placebo-treated patients) were nausea, abnormal (vivid, unusual, or strange) dreams, constipation, flatulence, and vomiting.
Table 1. Common Treatment Emergent AEs (%) in the Fixed-Dose, Placebo-Controlled Studies (HLGTs ≥5% of Patients in the 1 mg BID CHANTIX Group and More Commonly than Placebo and PT ≥1% in the 1 mg BID CHANTIX Group, and…
| Reaction | CHANTIX 0.5 mg BID N=129 | CHANTIX 1 mg BID N=821 | Placebo N=805 |
|---|---|---|---|
| Nausea | 16 | 30 | 10 |
| Abdominal Pain Includes PTs Abdominal (pain, pain upper, pain lower, discomfort,… | 5 | 7 | 5 |
| Flatulence | 9 | 6 | 3 |
| Dyspepsia | 5 | 5 | 3 |
| Vomiting | 1 | 5 | 2 |
| Constipation | 5 | 8 | 3 |
| Gastroesophageal reflux disease | 1 | 1 | 0 |
| Dry mouth | 4 | 6 | 4 |
| Insomnia Includes PTs Insomnia/Initial insomnia/Middle insomnia/Early morning awakening | 19 | 18 | 13 |
| Abnormal dreams | 9 | 13 | 5 |
| Sleep disorder | 2 | 5 | 3 |
| Nightmare | 2 | 1 | 0 |
| Headache | 19 | 15 | 13 |
| Dysgeusia | 8 | 5 | 4 |
| Somnolence | 3 | 3 | 2 |
| Lethargy | 2 | 1 | 0 |
| Fatigue/Malaise/Asthenia | 4 | 7 | 6 |
| Rhinorrhea | 0 | 1 | 0 |
| Dyspnea | 2 | 1 | 1 |
| Upper Respiratory Tract Disorder | 7 | 5 | 4 |
| Rash | 1 | 3 | 2 |
| Pruritis | 0 | 1 | 1 |
| Increased appetite | 4 | 3 | 2 |
| Decreased appetite/Anorexia | 1 | 2 | 1 |
Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.
From the label: adverse reactions, continuedThe following serious adverse reactions were reported in postmarketing experience and are discussed in greater detail in other sections of the labeling: • Neuropsychiatric Adverse Events including Suicidality [see Warnings and Precautions (5.1) ] • Seizures [see Warnings and Precautions (5.2) ] • Interaction with Alcohol [see Warnings and Precautions (5.3) ] • Accidental Injury [see Warnings and Precautions (5.4) ] • Cardiovascular Events [see Warnings and Precautions (5.5) ] • Somnambulism [see Warnings and Precautions (5.6) ] • Angioedema and Hypersensitivity Reactions [see Warnings and Precautions (5.7) ] • Serious Skin Reactions [see Warnings and Precautions (5.8) ] In the placebo-controlled premarketing studies, the most common adverse events associated with CHANTIX (>5% and twice the rate seen in placebo-treated patients) were nausea, abnormal (vivid, unusual, or strange) dreams, constipation, flatulence, and vomiting. The treatment discontinuation rate due to adverse events in patients dosed with 1 mg twice daily was 12% for CHANTIX, compared to 10% for placebo in studies of three months' treatment. In this group, the discontinuation rates that are higher than placebo for the most common adverse events in CHANTIX-treated patients were as follows: nausea (3% vs. 0.5% for placebo), insomnia (1.2% vs. 1.1% for placebo), and abnormal dreams (0.3% vs. 0.2% for placebo). …
Source: FDA drug label, NDA021928 (Pf Prism Cv), as published by Pfizer Laboratories Div Pfizer Inc, effective January 23, 2026 (SPL set f0ff4f27-5185-4881-a749-c6b7a0ca5696), via openFDA; the full label on DailyMed
What do FAERS reports show?
79,556 reports list varenicline among the medicines taken, each a report of something that happened, not proof the medicine caused it; 1,637 are coded as a death and 7,357 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 24 reactions below, 20 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.
Reports received each year
The 25 most reported reactions
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Varenicline: the full record
- label, generics, price, shortages, recalls
- Report a side effect to the FDA
- MedWatch
- Side effects hub
- the most reported medicines and reactions