What the label lists and what reports show
Flecainide side effects
Flecainide's FDA label: “Most Common Non-Cardiac Adverse Effects in Ventricular Arrhythmia Patients Treated with Flecainide in the Multicenter Study Adverse Effect Incidence All 429 Patients at Any Dose Incidence by Dose During Upward Titration 200 mg/Day (N=426) 300 mg/Day (N=293) …” FAERS holds 5,246 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 fatigue (287 reports).
- Generic listed
Check it at the source: the flecainide FDA label on DailyMed (effective June 11, 2026, Amneal Pharmaceuticals of New York LLC); the FDA FAERS public dashboard.
What does the label list?
From the label: adverse reactionsMost Common Non-Cardiac Adverse Effects in Ventricular Arrhythmia Patients Treated with Flecainide in the Multicenter Study Adverse Effect Incidence All 429 Patients at Any Dose Incidence by Dose During Upward Titration 200 mg/Day (N=426) 300 mg/Day (N=293) 400 mg/Day (N=100) […]
Table 1 Most Common Non-Cardiac Adverse Effects in Ventricular Arrhythmia Patients Treated with…
This table is printed in the Flecainide Acetate label published by Chartwell RX, LLC of October 28, 2024; the label quoted above does not print one.
| Adverse Effect | All 429 Patients at Any Dose | 200 mg/Day N=426) | 300 mg/Day N=293) | 400 mg/Day (N=100) |
|---|---|---|---|---|
| Dizziness | 18.9% | 11.0% | 10.6% | 13.0% |
| Visual Disturbances | 15.9% | 5.4% | 12.3% | 18.0% |
| Dyspnea | 10.3% | 5.2% | 7.5% | 4.0% |
| Headache | 9.6% | 4.5% | 6.1% | 9.0% |
| Nausea | 8.9% | 4.9% | 4.8% | 6.0% |
| Fatigue | 7.7% | 4.5% | 4.4% | 3.0% |
| Palpitation | 6.1% | 3.5% | 2.4% | 7.0% |
| Chest Pain | 5.4% | 3.1% | 3.8% | 1.0% |
| Asthenia | 4.9% | 2.6% | 2.0% | 4.0% |
| Tremor | 4.7% | 2.4% | 3.4% | 2.0% |
| Constipation | 4.4% | 2.8% | 2.1% | 1.0% |
| Edema | 3.5% | 1.9% | 1.4% | 2.0% |
| Abdominal Pain | 3.3% | 1.9% | 2.4% | 1.0% |
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, continuedIn post-myocardial infarction patients with asymptomatic PVCs and nonsustained ventricular tachycardia, flecainide therapy was found to be associated with a 5.1% rate of death and non-fatal cardiac arrest, compared with a 2.3% rate in a matched placebo group (see WARNINGS ). Adverse effects reported for flecainide, described in detail in the WARNINGS section, were new or worsened arrhythmias which occurred in 1% of 108 patients with PSVT and in 7% of 117 patients with PAF; and new or exacerbated ventricular arrhythmias which occurred in 7% of 1330 patients with PVCs, non-sustained or sustained VT. In patients treated with flecainide for sustained VT, 80% (51/64) of proarrhythmic events occurred within 14 days of the onset of therapy. 198 patients with sustained VT experienced a 13% incidence of new or exacerbated ventricular arrhythmias when dosage was initiated at 200 mg/day with slow upward titration, and did not exceed 300 mg/day in most patients. In some patients, flecainide treatment has been associated with episodes of unresuscitatable VT or ventricular fibrillation (cardiac arrest) (see WARNINGS ). New or worsened CHF occurred in 6.3% of 1046 patients with PVCs, non-sustained or sustained VT. Of 297 patients with sustained VT, 9.1% experienced new or worsened CHF. New or worsened CHF was reported in 0.4% of 225 patients with supraventricular arrhythmias. …
Source: FDA drug label, Amneal Pharmaceuticals of New York LLC, effective June 11, 2026 (SPL set ee9595d5-08a1-4529-9215-ddc3c7f929c4), via openFDA; the full label on DailyMed
What do FAERS reports show?
5,246 reports list flecainide among the medicines taken, each a report of something that happened, not proof the medicine caused it; 446 are coded as a death and 2,101 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 21 reactions below, 13 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?
- Flecainide: 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