What the label lists and what reports show
Sapropterin side effects
Sapropterin's FDA label: “Most common adverse reactions (≥4%) are: headache, rhinorrhea, pharyngolaryngeal pain, diarrhea, vomiting, cough, and nasal congestion.” FAERS holds 6,334 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 headache (378 reports).
- Generic listed
Check it at the source: the sapropterin FDA label on DailyMed (effective August 26, 2024, BioMarin Pharmaceutical 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 KUVAN?Kuvan can cause serious side effects, including: Severe allergic reactions. Stop taking Kuvan and get medical help right away if you develop any of these symptoms of a severe allergic reaction: wheezing or trouble breathing coughing feeling lightheaded or you faint flushing nausea rash Inflammation of the lining of the stomach (gastritis) or esophagus (esophagitis). Gastritis or esophagitis can happen with Kuvan and may be severe. Call your doctor right away if you have any of these signs or symptoms: severe upper stomach-area (abdominal) discomfort or pain, nausea and vomiting blood in your vomit or stool black, tarry stools difficulty swallowing loss of appetite pain in the throat Phe levels that are too low. Some children under the age of 7 years who take high doses of Kuvan each day may experience low Phe levels. Too much or constant activity (hyperactivity) can happen with Kuvan. […]
Source: FDA drug label, BioMarin Pharmaceutical Inc., effective August 26, 2024 (SPL set af38711e-8873-4790-a92d-4d583e23fb89), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsMost common adverse reactions (≥4%) are: headache, rhinorrhea, pharyngolaryngeal pain, diarrhea, vomiting, cough, and nasal congestion.
A table the label prints in its adverse reactions section without a title; its column headings name the groups compared
| Reaction | MedDRA Preferred Term KUVAN (N=74) No. Patients (%) | Treatment Placebo (N=59) No. Patients (%) |
|---|---|---|
| Headache | 11 (15) | 8 (14) |
| Rhinorrhea | 8 (11) | 0 |
| Pharyngolaryngeal pain | 7 (10) | 1 (2) |
| Diarrhea | 6 (8) | 3 (5) |
| Vomiting | 6 (8) | 4 (7) |
| Cough | 5 (7) | 3 (5) |
| Nasal congestion | 3 (4) | 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, continuedMost common adverse reactions (≥4%) are: headache, rhinorrhea, pharyngolaryngeal pain, diarrhea, vomiting, cough, and nasal congestion. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact BioMarin Pharmaceutical Inc. at 1-877-695-8826, 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 the rates in the clinical trials of another drug and may not reflect the rates observed in clinical practice. PKU Clinical Studies The safety of KUVAN was evaluated in 7 clinical studies in patients with PKU (aged 1 month to 50 years) [see Clinical Studies ( 14 )]. In Studies 1-4 (controlled and uncontrolled studies), 579 patients with PKU aged 4 to 49 years received KUVAN in doses ranging from 5 to 20 mg/kg per day for lengths of treatment ranging from 1 to 164 weeks. The patient population was evenly distributed in gender, and approximately 95% of patients were Caucasian. The most common adverse reactions (≥4% of patients) were headache, rhinorrhea, pharyngolaryngeal pain, diarrhea, vomiting, cough, and nasal congestion. …
Source: FDA drug label, BioMarin Pharmaceutical Inc., effective August 26, 2024 (SPL set af38711e-8873-4790-a92d-4d583e23fb89), via openFDA; the full label on DailyMed
What do FAERS reports show?
6,334 reports list sapropterin among the medicines taken, each a report of something that happened, not proof the medicine caused it; 74 are coded as a death and 435 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 20 reactions below, 8 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?
- Sapropterin: 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