Sephience (sepiapterin)
An approved treatment for Phenylketonuria.
The same compound appears under different names depending on the context. Here is how to identify Sepiapterin wherever you encounter it, plus the key facts at a glance.
- Generic name
- Sepiapterin
- Brand name
- Sephience
- Development codes
- PTC923, CNSA-001
- Drug class
- Phenylalanine hydroxylase (PAH) activator (BH4 precursor)
- Manufacturer
- PTC Therapeutics
- How it's taken
- Taken by mouth once a day with food, as a powder mixed into water or apple juice (or, for doses of 1,000 mg or more, strawberry jam or applesauce), followed by more food.
A once-daily oral powder approved by the FDA on July 28, 2025 to lower blood phenylalanine (Phe) in adults and children 1 month and older with PKU who respond to it, used together with a Phe-restricted diet. In its main trial, people who had responded during a 2-week test saw blood Phe fall by an average of 63% after 6 weeks, while it stayed about the same on placebo. Whether a person responds is found by trying it and measuring blood Phe.
Where Sepiapterin fits
One of 3 FDA-approved PKU medicines, alongside sapropterin (Kuvan and generics), a synthetic form of BH4 taken by mouth, and pegvaliase (Palynziq), an injected enzyme for people 12 and older whose Phe stays high. Sepiapterin and sapropterin are both used with a Phe-restricted diet in people whose blood Phe responds.
How Sepiapterin works
In PKU, the liver enzyme phenylalanine hydroxylase (PAH) does not work well enough, so phenylalanine (Phe), a building block of protein, builds up in the blood and can harm the brain. PAH needs a helper molecule called tetrahydrobiopterin (BH4) to work. Sepiapterin is a natural precursor that the body converts into BH4, and after a dose, blood levels of BH4 are far higher than levels of sepiapterin itself. By raising BH4, it activates PAH so more Phe can be broken down. Not everyone responds, and the label says response cannot generally be predicted by lab or genetic tests, so it is found by trying the drug and checking blood Phe.
Mechanism: Oral precursor that the body converts to tetrahydrobiopterin (BH4), the helper molecule the phenylalanine hydroxylase (PAH) enzyme needs to break down phenylalanine
Side effects and safety
- Increased bleeding. Bruising, prolonged bleeding and heavy menstrual bleeding have occurred. Tell your doctor about unusual bleeding; treatment may be paused during active bleeding.
- Low blood Phe (hypophenylalaninemia). Seen in some children. Blood Phe is monitored and the dose or diet adjusted, because Phe that stays too low for a long time has been linked to problems with development.
- Levodopa interaction. With another PAH activator, seizures, overstimulation and irritability were reported in people also taking levodopa. People on levodopa are watched for changes in neurological status.
- Blood Phe before starting and regularly during treatment, more often in children
- Regular reviews of dietary protein and Phe intake
- Blood pressure if you also take a PDE-5 inhibitor such as sildenafil
Sephience has no boxed warning and no contraindications. In the placebo-controlled part of the main trial the most common side effects, against placebo, were diarrhea (7% against 2%), headache (7% against 2%), abdominal pain (5% against 2%), low blood Phe (4% against 0%), yellow or orange stool (4% against 0%) and throat pain (4% against 2%). The label warns about increased bleeding, including bruising, prolonged bleeding and heavy periods, and about blood Phe dropping too low (hypophenylalaninemia) in some children, which is why blood Phe is checked often in children. People who take levodopa should be watched for changes such as seizures or irritability, based on reports with another PAH activator[1].
This is not a complete list of side effects. Talk to your doctor or pharmacist about what to expect and when to seek medical attention.
Taking Sepiapterin
Taken by mouth once a day with food, as a powder mixed into water or apple juice (or, for doses of 1,000 mg or more, strawberry jam or applesauce), followed by more food. The starting dose depends on age: 7.5 mg/kg a day under 6 months, 15 mg/kg from 6 months to under 1 year, 30 mg/kg from 1 to under 2 years, and 60 mg/kg for age 2 and older, which is also the maximum. In children under 2 the dose can be raised step by step if blood Phe does not drop, and treatment is stopped if blood Phe does not fall after 2 weeks at 60 mg/kg. Sepiapterin is taken along with a Phe-restricted diet, and medicines that block folate metabolism (such as methotrexate or trimethoprim) or sepiapterin reductase (such as sulfasalazine) should be avoided[1].
Availability and cost
Only available as the brand-name product.
Help paying for Sephience
Pick your insurance to see which help fits. Drugmaker copay cards can't be used with Medicare, Medicaid or TRICARE; charity funds are the usual route there.
- Copay help
Copay Assistance Program: low to no out-of-pocket costs for most patients who qualify. Not valid for prescriptions reimbursed in whole or in part by Medicaid or Medicare, including Medicare Part D.
For: private insurance · source - Bridge or quick-start supply
PTC Cares lists a Bridge Program for eligible patients. Contact PTC Cares for terms.
The official page does not say who qualifies. Ask the program. · source - Free medicine program
PTC Cares lists a Patient Assistance Program (PAP). Contact PTC Cares for eligibility.
The official page does not say who qualifies. Ask the program. · source
Good to know: Phone is 1-844-4PTCCARES. The program and its 3 parts were confirmed on the Sephience prescriber site; ptccares.com timed out, so Bridge and PAP eligibility details were not confirmed and the who fields are left empty.
- From a charity · NORD RareCarePhenylketonuria (PKU) Medical Assistance fundOpen
Pays for: Medical and medication costs.
The foundation says: “Accepting Applications” - From a charity · NORD RareCarePhenylketonuria (PKU) Premium Copay Assistance fundOpen
Pays for: Insurance premiums and copays.
The foundation says: “Accepting Applications”
Access and eligibility
Approved for adults and children 1 month and older with PKU whose blood Phe responds to sepiapterin, used with a Phe-restricted diet. Response has to be tested with a trial of the drug, since the label says lab or genetic tests cannot generally predict it. Safety and effectiveness in babies younger than 1 month have not been established. The main trial required at least 2 past blood Phe readings of 600 µmol/L or higher.
Source: PTC Cares for Sephience
Access program details are provided for informational purposes and may vary based on insurance coverage, geographic location, and individual circumstances. Confirm current eligibility directly with the manufacturer or your specialty pharmacy.
Clinical trial results
Approval rested on APHENITY (NCT05099640), a 2-part trial in people aged 1 to 61 with PKU and blood Phe of at least 600 µmol/L. In part 1, 157 people took sepiapterin for 14 days, and 66% saw blood Phe fall by 30% or more. In part 2, 98 of those responders aged 2 and older were randomized to sepiapterin or placebo for 6 weeks: blood Phe fell from an average of 646 to 236 µmol/L on sepiapterin, a 63% drop, while it stayed about the same on placebo (654 to 638 µmol/L)[1][4]. An ongoing open-label study supported use in children under 2[1].
Development history
PTC Therapeutics developed sepiapterin under the codes CNSA-001 and PTC923[6][5]. The FDA approved it as Sephience on July 28, 2025 for people 1 month and older with sepiapterin-responsive PKU, and PTC described the label as covering all PKU subtypes[2][3]. The European Commission had granted marketing authorization shortly before the US approval[3].
Explore Phenylketonuria trials
Common questions about Sepiapterin
▸What is Sepiapterin (Sephience)?
A once-daily oral powder approved by the FDA on July 28, 2025 to lower blood phenylalanine (Phe) in adults and children 1 month and older with PKU who respond to it, used together with a Phe-restricted diet. In its main trial, people who had responded during a 2-week test saw blood Phe fall by an average of 63% after 6 weeks, while it stayed about the same on placebo. Whether a person responds is found by trying it and measuring blood Phe.
▸How does Sepiapterin work?
In PKU, the liver enzyme phenylalanine hydroxylase (PAH) does not work well enough, so phenylalanine (Phe), a building block of protein, builds up in the blood and can harm the brain. PAH needs a helper molecule called tetrahydrobiopterin (BH4) to work. Sepiapterin is a natural precursor that the body converts into BH4, and after a dose, blood levels of BH4 are far higher than levels of sepiapterin itself. By raising BH4, it activates PAH so more Phe can be broken down. Not everyone responds, and the label says response cannot generally be predicted by lab or genetic tests, so it is found by trying the drug and checking blood Phe.
▸What are the side effects of Sepiapterin?
Sephience has no boxed warning and no contraindications. In the placebo-controlled part of the main trial the most common side effects, against placebo, were diarrhea (7% against 2%), headache (7% against 2%), abdominal pain (5% against 2%), low blood Phe (4% against 0%), yellow or orange stool (4% against 0%) and throat pain (4% against 2%). The label warns about increased bleeding, including bruising, prolonged bleeding and heavy periods, and about blood Phe dropping too low (hypophenylalaninemia) in some children, which is why blood Phe is checked often in children. People who take levodopa should be watched for changes such as seizures or irritability, based on reports with another PAH activator[1].
▸How is Sepiapterin taken?
Taken by mouth once a day with food, as a powder mixed into water or apple juice (or, for doses of 1,000 mg or more, strawberry jam or applesauce), followed by more food. The starting dose depends on age: 7.5 mg/kg a day under 6 months, 15 mg/kg from 6 months to under 1 year, 30 mg/kg from 1 to under 2 years, and 60 mg/kg for age 2 and older, which is also the maximum. In children under 2 the dose can be raised step by step if blood Phe does not drop, and treatment is stopped if blood Phe does not fall after 2 weeks at 60 mg/kg. Sepiapterin is taken along with a Phe-restricted diet, and medicines that block folate metabolism (such as methotrexate or trimethoprim) or sepiapterin reductase (such as sulfasalazine) should be avoided[1].
▸Is Sepiapterin FDA approved?
Yes, Sepiapterin (Sephience) is FDA approved (2025) for the treatment of Phenylketonuria.
▸How do I know if Sephience will work for me?
The label says response to sepiapterin generally cannot be predicted by lab or genetic tests. Your metabolic team checks your blood Phe before starting and again during the first weeks, and if blood Phe does not fall after 2 weeks at the top dose of 60 mg/kg a day, the drug is stopped. In the main trial, 66% of people had a drop of 30% or more within 2 weeks.
▸Do I still need the PKU diet on Sephience?
Yes. Sephience is approved for use together with a Phe-restricted diet. Your healthcare provider may adjust your protein and Phe intake based on your blood Phe levels, but do not change your diet without talking to them first.
▸What are the side effects of Sephience?
In the main trial the most common side effects were diarrhea (7% against 2% on placebo), headache, abdominal pain, low blood Phe, yellow or orange stool and throat pain. The label also warns about increased bleeding and about blood Phe dropping too low, especially in children.
Sources and references
Every factual claim on this page is drawn from the public sources listed below. Click any reference to open the original document.
- U.S. National Library of Medicine, DailyMed. SEPHIENCE (sepiapterin) oral powder: prescribing information. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=32ac719c-49f0-4105-9c46-18c19583a5c2
- U.S. Food and Drug Administration · 2025-07-28. NDA 219666 approval letter. https://www.accessdata.fda.gov/drugsatfda_docs/appletter/2025/219666Orig1s000ltr.pdf
- PTC Therapeutics · 2025-07-28. PTC Therapeutics Announces FDA Approval of Sephience (sepiapterin) for the Treatment of Children and Adults Living with Phenylketonuria (PKU). https://ir.ptcbio.com/news-releases/news-release-details/ptc-therapeutics-announces-fda-approval-sephiencetm-sepiapterin
- The Lancet · 2024. Effects of oral sepiapterin on blood Phe concentration in a broad range of patients with phenylketonuria (APHENITY): results of an international, phase 3, randomised, double-blind, placebo-controlled trial. https://doi.org/10.1016/S0140-6736(24)01556-3
- ClinicalTrials.gov. A Study of PTC923 in Participants With Phenylketonuria (APHENITY). https://clinicaltrials.gov/study/NCT05099640
- ClinicalTrials.gov. A Study of PTC923 (CNSA-001) in Primary Tetrahydrobiopterin (BH4) Deficient Participants With Hyperphenylalaninemia. https://clinicaltrials.gov/study/NCT03519711
- U.S. National Library of Medicine, DailyMed. KUVAN (sapropterin dihydrochloride) tablets and powder for oral solution: prescribing information. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=af38711e-8873-4790-a92d-4d583e23fb89
- U.S. National Library of Medicine, DailyMed. PALYNZIQ (pegvaliase-pqpz) injection, for subcutaneous use: prescribing information. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=6dba844a-db02-44f8-8593-ce497ed9406c
- PTC Therapeutics. Resources and Support: SEPHIENCE (sepiapterin) for HCPs. https://hcp.sephience.com/resources/