Phenylalanine

Phenylalanine is an essential amino acid used by the body to build proteins and to make tyrosine, which is converted into neurotransmitters (dopamine, norepinephrine, epinephrine) and thyroid hormones. As a supplement it’s used for mood disorders, depression, chronic pain and skin conditions such as vitiligo. People with phenylketonuria (PKU) must avoid phenylalanine because they cannot metabolize it safely.

Phenylalanine appears in some Coke products because they contain the artificial sweetener aspartame. Aspartame breaks down into phenylalanine, aspartic acid, and methanol during digestion, so phenylalanine is present in the drink. This gives intense sweetness with few calories. People with phenylketonuria (PKU) cannot metabolize phenylalanine and must avoid aspartame-containing beverages, which carry PKU warnings.

Phenylalanine warnings indicate the product contains this amino acid, which people with phenylketonuria (PKU) cannot properly metabolize. Due to a genetic deficiency of phenylalanine‑hydroxylase, phenylalanine builds up and can cause brain damage, developmental delay, and seizures. Newborns are screened for PKU; affected individuals must limit phenylalanine intake to prevent long‑term neurological harm.

Yes. Phenylalanine can cause side effects—especially when taken as a supplement—including nausea, heartburn, headache, anxiety, restlessness, insomnia and increased blood pressure. It is dangerous for people with phenylketonuria (PKU), who must avoid it, and may interact with MAO inhibitors or levodopa. Use caution in pregnancy, hypertension, or psychiatric conditions; consult a clinician before use.

Phenylethylamine occurs naturally in cocoa and chocolate (especially dark), and in some fermented or aged foods such as cheeses, soy products, and sauerkraut. It can also be present in certain processed meats, fermented beverages, and to a lesser extent in some nuts and seeds. Levels vary widely with processing and ripening, so chocolate and aged/fermented products are the most common dietary sources.

High-phenylalanine foods are protein-rich items such as meat (beef, pork, poultry), fish, eggs and dairy (milk, cheese, yogurt); soy products (tofu, tempeh, soy milk); legumes (beans, lentils, chickpeas); nuts and seeds (almonds, peanuts, sunflower seeds); and whole grains. Many high-protein processed foods and products containing the artificial sweetener aspartame also provide phenylalanine.