Unfortunately, the L-DOPA data as it pertains to long-term administration reflects a few disparaging effects: Degradation of Dopamine Ions, motor function fluctuation, and disruption of the Dopaminergic-Serotonergic pathway (and thereby the physiological detriments contained therein). However, the only long-term administration studies currently undertaken have been in respects to synthetic preparations of L-DOPA; therefore, it has been postulated that most of the negative connotations of L-DOPA are associated with Dopaminergic transmission in peripheral tissues, as well as residual "Dopamine Flooding" in the regions of the brain not responsible for production and transmission. Most clinical data surrounding synthetic LD reflects trace amounts of both LD and converted Dopamine in the Nigrostatial Tract - a circuit responsible for relaying Dopamine between the Substantia Nigra and regions of the PFC; such discoveries are indicative of inefficient crossing of the BBB, failed conversion of L-DOPA to D (due to the lack of concomitant decarboxylase inhibitor administration).
With all that being said, natural preparations of L-DOPA have not reflected any of these negative connotations; particularly, degradation of Dopamine ions in the Substantia Nigra, and inefficient transmission (via NT discovery). Further, the current clinical data also reflects the absence of dyskinesiac symptoms, thereby indicating that peripheral tissue transmission is absent, or at least diminished, in natural preparations. While more research is necessary, the data is overwhelmingly positive in term of long-term safety and efficacy concerns, as it pertains to natural LD vs., synthetic LD.