<p>Symptomatic postural hypotension has occurred when Carbidopa-Levodopa is added to the treatment of a patient receiving antihypertensive medicines. Therefore, when therapy with CarbidopaLevodopa is started, dosage adjustment of the antihypertensive medicine may be required. There have been rare reports of adverse reactions, including hypertension and dyskinesia, resulting from the concomitant use of tricyclic antidepressants and Carbidopa-Levodopa. Studies demonstrate a decrease in the bioavailability of Carbidopa and/or Levodopa when it is ingested with ferrous sulphate or ferrous gluconate. Dopamine-2 receptor antagonists (e.g., phenothiazines, butyrophenones and risperidone) and isoniazid may reduce the therapeutic effects of Levodopa. In addition, the beneficial effects of Levodopa in Parkinson&#39;s disease have been reported to be reversed by phenytoin and papaverine. Patients taking these medicines with Carbidopa-Levodopa should be carefully observed for loss of therapeutic response. Concomitant therapy with selegiline and Carbidopa-Levodopa may be associated with severe orthostatic hypotension not attributable to Carbidopa-Levodopa alone.</p>