START HERE
What is sepiapterin and could it be for me?
Sepiapterin is an oral medicine taken once a day. It enters cells where it helps the body's PAH enzyme work better, so blood phenylalanine (Phe) levels can come down. Some people find that it allows them to eat more natural protein.
Audio summary coming soon. Recording is in production. The player above will be activated once the file is available.
Video coming soon. The animation is in production. The player above will be activated once the file is available.
Where sepiapterin is approved today
Approval ages vary by country. Check the local prescribing information for your country.
- Europe, Australia, Switzerland: approved for all ages.
- United States, Canada: approved from 1 month of age, alongside a Phe-restricted diet.
For other countries, ask your metabolic team about local availability.
Both treatments work by helping the PAH enzyme. Sepiapterin reaches more cells and supports more variants of PKU than sapropterin alone.
Questions to bring to your team
This is not a diagnostic tool and it does not say whether sepiapterin is right for you. It is a starting list of questions to discuss with your metabolic clinic.
- Has my blood Phe ever been above 360 µmol/L? Could I be a candidate for a sepiapterin trial?
- Am I at an age that is approved for sepiapterin in my country?
- If I have already tried sapropterin or pegvaliase, would sepiapterin still be worth trying?
- If I am not currently following a strict Phe-restricted diet, can I still trial sepiapterin?
- If I am pregnant, breastfeeding, or planning a pregnancy, what should I know before starting or continuing sepiapterin?
Bring this page or these questions to your next clinic visit.
Note: This guide does not cover infants under 2 years of age. A separate document for that group is in preparation.
Always consult your healthcare provider before changing your diet, medicine, or treatment plan. This page is for general information only and does not replace medical advice.
YOUR JOURNEY
Three steps from start to long-term care
Tap a step on the timeline below to filter the cards by stage. The cards summarize the 2026 international consensus on diet and sepiapterin.
Tap a step to filter the cards
PRACTICAL HOW-TO
Putting it into practice
Take it with food that contains fat
Sepiapterin is absorbed better when taken within 30 minutes of a meal that contains fat. Either category below works - choose what fits your daily diet.
Tip: About 8 to 10 grams of fat in the meal is suggested for children over 2 years old. Optimal amounts have not yet been formally studied.
Bringing back natural protein, step by step
If your team confirms a long-term response to sepiapterin, your dietitian may guide you through these four stages. Pace and choices are individual - this is a map, not a fixed schedule.
-
Replace some special low-protein foods
Gradually swap a few low-protein or low-Phe products for regular versions, where blood Phe allows.
-
Add measured natural protein
Introduce moderate-protein foods in measured portions: protein-containing vegetables, whole-grain cereals, pulses, whole eggs, pre-portioned cheese, yogurt pots, measured volumes of milk, nuts and seeds.
-
Expand variety
Add other protein-rich foods according to tolerance: meat or fish products, soy-based products, tofu. Start with lower-protein versions before higher-protein ones.
-
Reduce protein substitute
As natural protein intake increases, your dietitian reduces the dose of protein substitute, in proportion, while keeping nutrition balanced.
Throughout these stages, food diaries and regular blood Phe checks guide every decision. Some people continue a small dose of protein substitute for safety.
SAFETY AND EVERYDAY LIFE
What to know about safety
Open each panel for practical guidance on side effects, illness, and stopping treatment. Discuss anything new or unexpected with your team.
What to expect day to day
Sepiapterin is generally well tolerated. The most common reported effects in studies were upper respiratory infections, headache, diarrhea, and abdominal pain. Stools may also change color while you are on treatment.
The mixed liquid tastes sweet, especially in apple juice, and the texture is a little thick. It can take time to get used to.
Some people notice mild, temporary tooth color change. This is resolved by normal brushing and rinsing the mouth with water after each dose.
Call your team if:
- a side effect lasts more than a few days or affects daily life;
- you have signs of an allergic reaction (rash, swelling, trouble breathing) - seek urgent care;
- your blood Phe drops below 30 µmol/L on repeated tests.
Sick-day plan
During fever or illness, blood Phe levels often rise. Sepiapterin-specific data on illness are still limited, so the consensus is to keep the same level of vigilance you would use during sapropterin treatment.
Practical steps:
- follow your clinic's existing sick-day plan;
- keep fluids and energy intake up;
- if you have reduced or stopped your protein substitute, your team may ask you to use a small dose of it temporarily during illness;
- contact your clinic if symptoms last or you cannot keep food and fluids down.
If sepiapterin is stopped
If sepiapterin is stopped and no other Phe-lowering medicine is started, blood Phe will rise again. Your team will help you return to your previous Phe-restricted diet right away.
Reasons treatment may be paused or stopped include: not enough effect, side effects, difficulty taking the medicine, pregnancy, breastfeeding, or planning a pregnancy.
If you are pregnant, breastfeeding, or planning a pregnancy, talk with your team in advance about whether sepiapterin should continue. Strict blood Phe control during pregnancy is essential to protect the baby.