Phenylalanine Side Effects
For the most part, side effects of phenylalanine do not occur, especially when it is obtained through dietary sources. Problems may occur in unusually high doses, however. In addition, people with certain medical conditions, such as PKU, tardive dyskinesia, and Parkinson's, may be more susceptible to side effects. If you experience a negative reaction while taking phenylalanine supplements, contact your healthcare provider right away.
As with any medication or supplement, side effects are possible with phenylalanine. Although a normal dietary intake does not usually cause problems for most people, unusually high doses may cause side effects. In addition, people with certain medical conditions may be more susceptible to adverse reactions.
(The article discusses most, but not all possible side effects of phenylalanine. Your healthcare provider can discuss a more complete list of potential side effects with you.)
You may have read on the Internet about the many dangers of phenylalanine, but it is not likely to cause any problems in healthy people. Studies of phenylalanine in rats (and, therefore, reports of side effects in rats) cannot be applied to humans, due to important species differences between the two.
People with phenylketonuria (PKU), a rare genetic condition, cannot normally process phenylalanine in the body. If people with PKU ingest too much phenylalanine, serious problems could occur, especially brain and mental problems in children.
Studies have suggested that phenylalanine may worsen tardive dyskinesia in people with schizophrenia. Tardive dyskinesia is a movement disorder caused by antipsychotic medications. Studies also indicate that phenylalanine (as well as several other amino acids) may worsen some of the symptoms of Parkinson's disease, which is why some people think a low-protein, low-amino acid diet may be helpful for people with this condition.