What the label lists and what reports show
Entacapone side effects
Entacapone's FDA label lists its adverse reactions in its own words. FAERS holds 4,154 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 hallucination (496 reports).
- Generic listed
Check it at the source: the entacapone FDA label on DailyMed (effective November 30, 2023, Sandoz Inc); the FDA FAERS public dashboard.
What does the label list?
From the label: adverse reactionsBecause clinical studies are conducted under widely varying conditions, the incidence of adverse reactions (number of unique patients experiencing an adverse reaction associated with treatment per total number of patients treated) observed in the clinical studies of a drug cannot be directly compared to the incidence of adverse reactions in the clinical studies of another drug and may not reflect the incidence of adverse reactions observed in practice. A total of 1,450 patients with Parkinson’s disease were treated with entacapone in premarketing clinical studies. Included were patients with fluctuating symptoms, as well as those with stable responses to levodopa therapy. All patients received concomitant treatment with levodopa preparations, however, and were similar in other clinical aspects. …
Table 4: Summary of Patients with Adverse Events after Start of Trial Drug Administration at least 1% in Entacapone Group and Greater Than Placebo
| SYSTEM ORGAN CLASS Preferred Term | Entacapone (n = 603) % of patients | Placebo (n = 400) % of patients |
|---|---|---|
| Sweating increased | 2 | 1 |
| Back pain | 2 | 1 |
| Dyskinesia | 25 | 15 |
| Hyperkinesia | 10 | 5 |
| Hypokinesia | 9 | 8 |
| Dizziness | 8 | 6 |
| Taste perversion | 1 | 0 |
| Anxiety | 2 | 1 |
| Somnolence | 2 | 0 |
| Agitation | 1 | 0 |
| Nausea | 14 | 8 |
| Diarrhea | 10 | 4 |
| Abdominal pain | 8 | 4 |
| Constipation | 6 | 4 |
| Vomiting | 4 | 1 |
| Mouth dry | 3 | 0 |
| Dyspepsia | 2 | 1 |
| Flatulence | 2 | 0 |
| Gastritis | 1 | 0 |
| Gastrointestinal disorders | 1 | 0 |
| Dyspnea | 3 | 1 |
| Purpura | 2 | 1 |
| Urine discoloration | 10 | 0 |
| Back pain | 4 | 2 |
| Fatigue | 6 | 4 |
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.
Source: FDA drug label, NDA020796 (Orion Pharma), as published by Sandoz Inc, effective November 30, 2023 (SPL set ad4b6d79-efd3-4c43-b4dc-5afdacf939a4), via openFDA; the full label on DailyMed
What do FAERS reports show?
4,154 reports list entacapone among the medicines taken, each a report of something that happened, not proof the medicine caused it; 639 are coded as a death and 1,413 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 22 reactions below, 9 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?
- Entacapone: 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