The side effects of DL-phenylalanine, a form of phenylalanine, include hyperactivity and anxiety in children and abnormal facial movements in people who take antipsychotic medications, according to the University of Maryland Medical Center. Phenylalanine can cause injury to the brain of people with phenylketonuria.
The build-up of phenylalanine leads to problems such as high blood pressure and risk of stroke. Pregnant women with phenylketonuria are especially susceptible to experiencing severe side effects of phenylalanine, and too much of it can cause birth defects, explains WebMD. Although the body needs phenylalanine, an amino acid, to function, people with phenylketonuria, or PKU, cannot use phenylalanine because their body is not able to convert it, notes the University of Maryland Medical Center. Instead of eating foods with phenylalanine, people with phenylketonuria must take tyrosine supplements to bypass their body's inability to change the phenylalanine into tyrosine.
People with a phenylalanine deficiency may experience tiredness and trouble remembering things, states the University of Maryland Medical Center. Found in three forms, phenylalanine has been used in the treatment of depression, and research has been conducted in the usefulness of the amino acid in treating vitiligo and chronic pain. L-phenylalanine, the natural form of phenylalanine, can be found in foods such as eggs, dairy products, tofu and aspartame.