3,4-Dihydroxy-L-phenylalanine, commonly known as L-DOPA, is primarily used in the treatment of Parkinson's disease. It crosses the blood-brain barrier and is converted into dopamine, replenishing depleted levels in the brain to alleviate symptoms such as tremors, muscle stiffness, and slow movement. It is also under study for other dopamine-related conditions, including Restless Legs Syndrome and certain types of depression. Additionally, it is employed in research to study neurotransmitter function and the mechanisms of neurological disorders. In cosmetics, it serves as an ingredient in self-tanning products due to its ability to promote melanin production. It also finds use in biochemical studies to understand the synthesis and metabolism of catecholamines. Its use requires medical supervision due to potential side effects such as nausea, vomiting, or abnormal movements.