<p>Levodopa is a prodrug of dopamine that is administered to patients with Parkinson's due to its ability to cross the blood-brain barrier<sup class="text-reference-group"><a class="reference-popover-link" data-content="Official drug label" href="#label-reference">Label</a></sup>. Levodopa can be metabolised to dopamine on either side of the blood-brain barrier and so it is generally administered with a dopa decarboxylase inhibitor like carbidopa to prevent metabolism until after it has crossed the blood-brain barrier<sup class="text-reference-group"><a class="reference-popover-link" data-content="Official drug label" href="#label-reference">Label</a>,<a class="reference-popover-link" data-content="Djamshidian A, Poewe W: Apomorphine and levodopa in Parkinson's disease: Two revolutionary drugs from the 1950's. Parkinsonism Relat Disord. 2016 Dec;33 Suppl 1:S9-S12. doi: 10.1016/j.parkreldis.2016.12.004. Epub 2016 Dec 22. (PubMed ID 28012951)" href="#reference-A177781">1</a></sup>. Once past the blood-brain barrier, levodopa is metabolized to dopamine and supplements the low endogenous levels of dopamine to treat symptoms of Parkinson's<sup class="text-reference-group"><a class="reference-popover-link" data-content="Official drug label" href="#label-reference">Label</a></sup>. The first developed drug product that was approved by the FDA was a levodopa and carbidopa combined product called Sinemet that was approved on May 2, 1975<sup class="text-reference-group"><a class="reference-popover-link" data-content="Djamshidian A, Poewe W: Apomorphine and levodopa in Parkinson's disease: Two revolutionary drugs from the 1950's. Parkinsonism Relat Disord. 2016 Dec;33 Suppl 1:S9-S12. doi: 10.1016/j.parkreldis.2016.12.004. Epub 2016 Dec 22. (PubMed ID 28012951)" href="#reference-A177781">1</a>,<a class="reference-popover-link" data-content="FDA Approved Drug Products: Sinemet" href="#reference-L6133">7</a></sup>.</p>