Phenylalanine Side Effects and Warnings

Safety Issues

The long-term safety of phenylalanine in any of its forms is not known. Both L- and D-phenylalanine must be avoided by those with the rare metabolic disease phenylketonuria (PKU).

The maximum safe dosages of phenylalanine have not been established for young children, pregnant or nursing women, or those with severe liver or kidney disease.

There are some indications that the combined use of phenylalanine with antipsychotic drugs might increase the risk of developing the long-term side effect known as tardive dyskinesia, or worsen symptoms in those who already have it. ¹ Like other amino acids, phenylalanine may interfere with the absorption or action of the drug levodopa, which is used for Parkinson's disease . ²

Interactions You Should Know About

If you are taking:

• Antipsychotic medications : Do not use phenylalanine.

• Levodopa : Like other amino acids, phenylalanine might interfere with its action.