Figure. No caption available.
QAre herbal extracts containing L-dopa effective and safe for treating vascular parkinsonism?
DR. SOTIRIOS PARASHOS RESPONDS:
A In vascular parkinsonism, symptoms such as slow movements, tremor, difficulty with walking and balance, and stiffness are produced by one or more small strokes rather than by gradual loss of nerve cells, as seen in the much more common Parkinson's disease (PD).
L-dopa is the basic molecule used by certain nerve cells to make dopamine, which is in low supply in the brains of people with PD. L-dopa and similar molecules are found in some foods and in some nutritional supplements. When L-dopa is ingested, it is absorbed into the bloodstream and then quickly metabolized (broken down) by an enzyme called dopa decarboxylase (DDC), which is found in the kidneys, the liver, the lungs, and other tissues. Thus, by the time it makes it to the brain, only 1 to 3 percent of the ingested quantity of L-dopa remains.
When scientists first tried to use L-dopa to treat PD, they were unsuccessful. It was not until extremely high doses of the drug were used that patients' PD symptoms improved. However, the doses were so high that many people experienced severe nausea and vomiting. In the 1970s, L-dopa was coupled with one of two other drugs: carbidopa or benserazide. They both work in the same way, by blocking the enzyme DDC in all tissues of the body except the brain. As a result, 10 percent or more of the ingested L-dopa could make it to the brain, where it is needed. These other drugs allowed a dramatic decrease in the necessary dose of L-dopa, reducing nausea and vomiting, and made the effect L-dopa on PD symptoms more robust and consistent.
The small amount of L-dopa found in supplements, especially when not coupled with a drug like carbidopa, is unlikely to have any considerable benefit on PD symptoms. Occasionally, patients in my practice notice some benefit from these supplements. This may be because they were experiencing the placebo effect (a benefit caused by a person's anticipation that a treatment will help) or possibly because they were also taking other medications for PD and the small supply of L-dopa in the supplement was enough to make them feel a little better. So, L-dopa supplements are not likely to provide any symptom relief.
In addition, one should keep in mind that supplements do not generally go through the vigorous safety testing that pharmaceuticals do. Therefore, the safety of these supplements is best judged by the reliability of the manufacturer, any reports that may have been made to the U.S. Food & Drug Administration, and always after a discussion with your doctor. Your doctor can review the components of the supplements (ingredients are not always listed, but a reliable manufacturer should be willing and able to provide this information upon request) and advise you as to whether the supplements are safe to take, while taking into account any other medical conditions you may have and other medications that you already take.
Some people with vascular parkinsonism will have a partial response to L-dopa, while the majority will have either no response or a temporary improvement. If I see a robust response to L-dopa in a patient with vascular parkinsonism, I would be more likely to question the diagnosis and conclude that they have PD proper.