Twenty-seven studies (n=654) were included in the review, of which two were randomised controlled trials (RCTs, n=46).
Of the 27 included studies, 18 were open label (67%), 5 were double-blind (19%), 4 were single-blind (15%), 8 were placebo- controlled (30%), 17 used formalised rating scales (63%), 6 used formal diagnostic criteria (22%), and 6 included asymptomatic patients (22%).
The addition of L-dopa to APD treatment was beneficial when the results of 5 placebo-controlled trials were pooled (mean Cohen's d 0.7116, P<0.00001). However, there was statistically significant heterogeneity between the studies.
From the 16 open trials, when added to APD treatment, the median proportion of people that were better with L-dopa treatment was 45.8% (mean 42.4%). The median proportion of people that were worse with L-dopa treatment was 9.2% (mean 22.2%).