Depression — whether a disease symptom or a response to PD disability — affects many Parkinson's patients. Long-term levodopa treatment may actually contribute to the problem. Treatment with S-adenosylmethionine (SAMe), a natural substance in cells and sometimes used as an antidepressant, has been suggested in treating PD symptoms of depression. However, SAMe depletes dopamine and can produce PD-like changes in animals, causing cell degeneration in the nigra and striatum areas of the brain. [1]

Similarly, the herb kava (Piper methysticum) may counter the effects of dopamine and reduce the effectiveness of PD medication. [2]

References

1. Charlton CG.
Depletion of nigrostriatal and forebrain tyrosine hydroxylase by S-adenosylmethionine: a model that may explain the occurance of depression in Parkinson's disease.
Life Sciences 1997;61:495-502.

2. Schelosky L, et al.
Kava and dopamine antagonism.
J Neurol Neurosurg Psychiatry 1995;58:639-40.