Levodopa is an intermediate step in the metabolization of the hormone dopamine from the amino acid tyrosine. Tyrosine may also metabolize into epinephrine or norepinephrine, also with levodopa as an intermediate product. In medicine, levodopa is prescribed to patients suffering from Parkinson's disease, as many of their symptoms are caused by a lack of natural dopamine in the brain.
Swedish scientist Arvid Carlsson pioneered the use of levodopa for patients with Parkinson's symptoms in the 1950s and won a Nobel Prize for his work in medicine in 2000. Neurologist Oliver Sacks discussed his experiences with levodopa therapy in his 1973 book Awakenings, adapted to film in 1990. 2001 Nobel Prize winner William S. Knowles developed a new method of synthesizing many pharmaceuticals which was primarily used for levodopa.
There are a few concerns with the use of levodopa to treat Parkinson's disease. Dopamine cannot be administered because it is blocked by the blood-brain barrier and cannot enter the patient's brain, but large amounts of levodopa become metabolized into dopamine in the patient's peripheral nervous system (PNS) before even reaching the blood-brain barrier. This results in a number of adverse side effects, especially in the long term.
Side effects of levodopa use may include low blood pressure, arrhythmia, nausea, hair loss, confusion, emotional disturbances, gastrointestinal bleeding, insomnia, and hallucinations. When used long term, levodopa may begin to decrease in effectiveness and may cause dyskinesia, or impairment of voluntary movement. As a result, doctors prescribe levodopa sparingly and often include peripheral DOPA decarboxylase inhibitors to limit the amount of levodopa metabolized in the PNS. Despite these concerns, levodopa is believed to be safer than other drugs used to treat Parkinson's.
Levodopa is also available in relatively small doses in over-the-counter supplement form. It is claimed to support body building and increase libido by increasing testosterone. Neither these claims nor possible side effects have been clinically evaluated. Remember to discuss any supplements you are considering taking with your doctor or nutritionist.