The objective of this clinical study is to examine the effects of a Chinese herbal medicine formula (Jia Wei Liu Jun Zi Tang: JWLJZT) on motor and non-motor symptoms, and on complications of conventional therapy in idiopathic Parkinson's disease (PD), using an add-on design. Fifty-five patients with PD were randomly allocated to receive either Chinese herbal medicine or placebo for 24 weeks. Primary outcome measure was the 39-item Parkinson's Disease Questionnaire (PDQ-39). Secondary outcome measures included the Unified Parkinson's Disease Rating Scale (UPDRS), Short-Form-36 Health Survey (SF-36), Geriatric Depression Scale (GDS), home diaries, and a range of category rating scales. JWLJZT resulted in a significant improvement in the UPDRS IVC when compared with placebo at 12 weeks (P =.039) and 24 weeks (P =.034). In addition, patients in the Chinese herbal medicine group also showed significant improvement in PDQ-39 communication scores at 12 weeks (P =.024) and 24 weeks (P =.047) when compared with the placebo group. There were no significant differences between treatment and control groups for SF-36 variables, GDS score or the mean daily "on-off" time. One case of mild diarrhea was noted in the treatment group. The findings suggest that JWLJZT can relieve some non-motor complications of conventional therapy and improve the communication ability in patients with PD. The results of this pilot study warrant larger multi-center clinical studies to assess long-term efficacy and tolerability of JWLJZT, and to elucidate the mechanisms by which it affects PD function. Copyright © 2011 Wan Fung Kum et al.