What unpleasant side effect results from L-DOPA being converted prematurely in peripheral systems?
Severe nausea and vomiting.
When L-DOPA is administered without its inhibitor, Carbidopa, a significant portion of the drug is metabolized into dopamine by DOPA decarboxylase enzymes located in the peripheral tissues, such as the bloodstream, rather than waiting to be converted inside the brain. This premature conversion of L-DOPA into dopamine outside the central nervous system is highly problematic. While dopamine is useful in the brain, its presence in the peripheral circulation causes substantial gastrointestinal distress. The text specifically highlights that this peripheral dopamine generation results in very unpleasant side effects, most notably severe nausea and vomiting, which severely limits the practicality of using L-DOPA as a monotherapy for long-term management.
