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Side Effects of L-Phenylalanine

author image Rae Uddin
Rae Uddin has worked as a freelance writer and editor since 2004. She specializes in scientific journalism and medical and technical writing. Her work has appeared in various online publications. Uddin earned her Master of Science in integrated biomedical sciences with an emphasis in molecular and cellular biochemistry from the University of Kentucky College of Medicine.
Side Effects of L-Phenylalanine
Doctor talking with patient. Photo Credit: 4774344sean/iStock/Getty Images

Phenylalanine is a type of amino acid that your body uses to generate proteins and certain types of chemicals in the brain. There are three forms of phenylalanine: L-phenylalanine, the naturally-occurring form of this amino acid; D-phenylalanine, a synthetic form of this amino acid; and DL-phenylalanine, a combination of the first two forms of this amino acid. Talk with your doctor if you experience side effects after consuming food items that contain L-phenylalanine.

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Darkening of the Skin

Consuming L-phenylalanine may cause unusual darkening of your skin, a side effect called hyperpigmentation. Hyperpigmentation may occur across any region of your body, but may be most apparent on your facial skin. This side effect of L-phenylalanine may be bothersome and can result in permanent or lasting skin discoloration. Alternatively, this effect of L-phenylalanine may be beneficial for people who have vitiligo, a condition in which white patches of skin develop across the body, the University of Maryland Medical Center explains.

Phenylketonuria Symptoms

L-phenylalanine may induce severe side effects in people who have a medical condition called phenylketonuria. Phenylketonuria, also called PKU, is an inherited genetic condition that prevents the body from synthesizing the enzyme required to break down phenylalanine. Symptoms associated with PKU typically develop in affected infants shortly after birth. PKU symptoms include seizures, skin rash, hyperactivity, social or behavioral problems, stunted growth, or mental retardation, reports. You may also notice that your infant's urine, skin or breath emits an unusually musty odor. If your infant exhibits any of these symptoms, have him evaluated by a medical professional as soon as possible. PKU symptoms can be managed by reducing and controlling the amount of phenylalanine your infant consumes.

DL-Phenylalanine Side Effects

Additional side effects may occur following treatment with supplements that contain DL-phenylalanine. Children receiving DL-phenylalanine supplements may appear unusually hyperactive or anxious, UMMC reports. High doses of this supplement may also cause headache pain or stomach-related side effects, such as heartburn or nausea. If these side effects persist or become severe, seek additional care from your doctor.

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