two recent Cochrane reviews (Storebo et al, 2015; Punja et al, 2016a) questioned the quality of the evidence from available RCTs (see also a previous Mental Elf blog by Chris Hollis on this review).

Whilst meta-analyses of interventions (such as the available ones on ADHD drugs) often include parallel RCTs, no meta-analysis so far had pooled n-of-1 trials, defined as multiple crossover trials performed in a single participant, often with randomisation and blinding. Meta-analysing data from n-of-1 trials would allow aggregating data on individual response to treatment.

Punja and colleagues (Punja et al, 2016b) performed the first meta-analysis of n-of-1 trials, focusing on psychostimulants (methylphenidate and amphetamine derivatives) for ADHD, for which numerous N-of-1 trials have been published.