Study	Reason for exclusion
Bentovim 1968	Unclear if randomised and dietary treatment not initiated soon after birth in all participants.
Cleary 2006	Trial of a specific supplement.
Epstein 1989	Not a randomised controlled trial.
Frankenburg 1973	Not a randomised controlled trial.
Kakanoglu 2005	Participants not eligible ‐ paper states 'participants previously untreated'.
Koff 1979	Not a randomised controlled trial.
Koletzko 2007	Trial of a fatty acid supplement.
Krause 1985	Not a randomised controlled trial.
Levy 2007	Trial of a specific supplement.
Lou 1987	Trial of an additional supplement.
Pietz 1995	Trial of tyrosine.
Realmuto 1986	Introduced phenylalanine for one day only.
Rey 1996	Not a randomised controlled trial.
Robertson 2004	Participants previously untreated.
Schindeler 2007	Trial of an additional supplement.
Schmidt 1994	Not a randomised controlled trial.
Schmidt 1996	Not a randomised controlled trial.
Smith 1998	Trial of tyrosine.