Can You Take DL-Phenylalanine and L-Tryptophan Together?

May affect absorption

The short answer

DL-Phenylalanine and L-Tryptophan are both large neutral amino acids (LNAAs) that compete for the same blood-brain barrier transporter (LAT1). Taking them together reduces brain uptake of both.

How to arrange timing

Separate DL-Phenylalanine and L-Tryptophan by at least 2 hours for optimal brain uptake of each.

Reference

Reference noted for this combination: Fernstrom JD. Large neutral amino acids: dietary effects on brain neurochemistry and function. Amino Acids. 2013;45(3):419-430.

Important context

Whether supplements suit you together also depends on dose, product formulation, health conditions, and medication use. Ask a doctor or pharmacist first if you take medication, are pregnant or breastfeeding, or have a chronic condition.