What the label lists and what reports show
Glycerol phenylbutyrate side effects
Glycerol phenylbutyrate's FDA label: “Most common adverse reactions (≥ 10%) in adults are: diarrhea, flatulence, and headache.” FAERS holds 1,358 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 ammonia increased (197 reports).
- Generic listed
- A presentation discontinued
Check it at the source: the glycerol phenylbutyrate FDA label on DailyMed (effective October 29, 2025, Horizon Therapeutics USA, 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 RAVICTI?RAVICTI may cause serious side effects, including: See " What is the most important information I should know about RAVICTI? " The most common side effects of RAVICTI in adults include: diarrhea gas headache abdomen (stomach) pain vomiting tiredness decreased appetite indigestion or heartburn The most common side effects of RAVICTI in children 2 years to 17 years of age include: upper abdomen (stomach) pain rash nausea vomiting diarrhea decreased appetite headache The most common side effects of RAVICTI in children 2 months to less than 2 years of age include: low white blood cell count (neutropenia) vomiting constipation diarrhea fever reduced food intake cough stuffy nose runny nose skin rash small round bumps on the skin The most common side effects of RAVICTI in children less than 2 months of age include: vomiting rash gastroesophageal reflux increased levels of liver enzymes in the […]
Source: FDA drug label, Horizon Therapeutics USA, Inc., effective October 29, 2025 (SPL set 900e7dc0-9afe-4f50-80de-90567bb78519), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsMost common adverse reactions (≥ 10%) in adults are: diarrhea, flatulence, and headache.
Table 1: Adverse Reactions Reported in 2 or More Adult Patients with UCDs (at least 4% in Either Treatment Arm) in Study 1
| Reaction | Sodium Phenylbutyrate (N = 45) | RAVICTI (N = 44) |
|---|---|---|
| Diarrhea | 3 (7) | 7 (16) |
| Headache | 4 (9) | 6 (14) |
| Flatulence | 1 (2) | 6 (14) |
| Abdominal pain | 2 (4) | 3 (7) |
| Vomiting | 2 (4) | 3 (7) |
| Decreased appetite | 2 (4) | 3 (7) |
| Fatigue | 1 (2) | 3 (7) |
| Dyspepsia | 3 (7) | 2 (5) |
| Nausea | 3 (7) | 1 (2) |
| Dizziness | 4 (9) | 0 |
| Abdominal discomfort | 3 (7) | 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, continuedThe following clinically significant adverse reactions are described elsewhere in the labeling: Neurotoxicity [see Warnings and Precautions (5.1) ] Pancreatic insufficiency or Intestinal Malabsorption [see Warnings and Precautions (5.2) ] Most common adverse reactions (≥ 10%) in adults are: diarrhea, flatulence, and headache. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Amgen Inc. at 1-800-77-AMGEN (1-800-772-6436) or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in clinical practice. Assessment of adverse reactions was based on exposure of 45 adult patients (31 female and 14 male) with UCD subtype deficiencies of ornithine transcarbamylase (OTC, n = 40), carbamoyl phosphate synthetase (CPS, n = 2), and argininosuccinate synthetase (ASS, n = 1) in a randomized, double-blind, active-controlled (RAVICTI vs sodium phenylbutyrate), crossover, 4-week study (Study 1) that enrolled patients 18 years of age and older [see Clinical Studies (14.1) ]. One of the 45 patients received only sodium phenylbutyrate prior to withdrawing on Day 1 of the study due to an adverse reaction. …
Source: FDA drug label, Horizon Therapeutics USA, Inc., effective October 29, 2025 (SPL set 900e7dc0-9afe-4f50-80de-90567bb78519), via openFDA; the full label on DailyMed
What do FAERS reports show?
1,358 reports list glycerol phenylbutyrate among the medicines taken, each a report of something that happened, not proof the medicine caused it; 65 are coded as a death and 601 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, 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?
- Glycerol phenylbutyrate: 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