Diarrhoea and changes in the colour of your stools are not a consequence of Parkinson’s disease or a direct side-effect of Parkinson’s medication.
L-dopa medication can cause diarrhoea, usually at the start of treatment, as can the COMT inhibitor entacapone (found in the combination tablet Stalevo – levodopa/carbidopa/entacapone) or as separate supplementary tablets such as Comtess / Entacapone), but this is not something that should be allowed to continue.
Dark stools may indicate the presence of blood, or possibly iron tablets, but should be investigated. It is usually local health centres that are best equipped to carry out these investigations, rather than neurology clinics.
/Håkan Widner