Inclusion Criteria:  age ≥ 18 years diagnosis of classical PKU (blood phenylalanine ≥1200 µmol pre-treatment or off-treatment ≥ 2 PKU-related symptoms with clinically meaningful negative impact on daily life is in regular clinical monitoring and is treated with a PKU diet with a natural protein restriction and medical foods average blood phenylalanine levels between 360 and 900 µmol in past one year able and willing to provide consent demonstrates capacity to complete all requirements of the protocol if on medications approved by the Principal Investigator agrees not to alter dose for duration of study has stable daily access to phone, internet, and physical address  Exclusion Criteria:  women who are breastfeeding, pregnant or planning to become pregnant in the next year use of adjuvant PKU treatments (LNAAs, Kuvan®, Palinziq®) within past 3 months use of psychotropic medications, melatonin, or any serotonin-reuptake inhibitors within past 3 months demonstrates insufficient motivation or time required to complete full trial