The response lasts. Most placebo effect seen in people with severe symptoms or surgery. In 16% of people on placebo, they felt 55% reduction in symptoms. Wish we could all harness this improvement somehow.

Mov Disord. 2008 Jan 28 [Epub ahead of print]
Placebo response in Parkinson's disease: Comparisons among 11 trials covering medical and surgical interventions.

Placebo responses were temporally distributed similarly during early, mid, and late phases of follow-up. Placebo-related improvements occur in most PD clinical trials and are similarly distributed across all 6 months of follow-up.

http://www.ncbi.nlm.nih.gov/sites/en..._uids=18228568