Side Effects & Safety L-phenylalanine is LIKELY SAFE for most people when taken by mouth in amounts commonly found in foods.



L-Phenylalanine is POSSIBLY SAFE when taken by mouth as medicine or when applied as a cream, short-term.



There is not enough reliable information available about the safety of D-phenylalanine.



Special Precautions & Warnings: Pregnancy and breast-feeding: Phenylalanine is LIKELY SAFE when consumed in amounts commonly found in foods by pregnant women who have normal phenylalanine levels. However, having too much phenylalanine in the mother's system during pregnancy can increase the chances of birth defects. The risk for facial defects is highest at weeks 10-14, nervous system and growth defects between 3-16 weeks, and heart defects at 3-8 weeks. For women who process phenylalanine normally and have normal levels, it is probably fine to get the amount of phenylalanine found in food, but not in higher doses. Do not take supplements. For women who have high levels of phenylalanine, even normal food amounts are UNSAFE. Additionally, experts recommend a low phenylalanine diet for at least 20 weeks before getting pregnant. This should reduce the risk of birth defects.



Phenylalanine is LIKELY SAFE for breast-feeding mothers whose bodies' process phenylalanine normally to consume the amount of phenylalanine found in food. However, do not take more. Not enough is known about the safety of taking phenylalanine in medicinal amounts during breast-feeding.



Phenylketonuria (PKU) and other conditions that cause high levels of phenylalanine: Phenylalanine should be avoided in people with certain inherited disorders that cause their bodies to build up too much phenylalanine. Phenylketonuria (PKU) is one of these diseases. People with this disorder can develop mental retardation, high blood pressure, stroke, and many other serious health issues if they consume phenylalanine. PKU is so serious that babies are screened at birth to determine whether they have the disorder and will need a special diet to avoid these problems.



Schizophrenia: Use with caution. Phenylalanine can make a movement disorder (tardive dyskinesia) in people with schizophrenia worse.



